ORCID Profile
0000-0002-4632-1024
Current Organisations
University of Greenwich
,
Coventry University
,
Aarhus Universitet
,
University of Western Australia
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Publisher: American Chemical Society (ACS)
Date: 24-06-2010
DOI: 10.1021/JP103858Z
Publisher: American Chemical Society (ACS)
Date: 25-02-2010
DOI: 10.1021/CM903659G
Publisher: International Union of Crystallography (IUCr)
Date: 10-1993
Publisher: American Chemical Society (ACS)
Date: 22-06-2020
Publisher: American Chemical Society (ACS)
Date: 04-12-2008
DOI: 10.1021/CM802289N
Publisher: AIP
Date: 2012
DOI: 10.1063/1.4731503
Publisher: Wiley
Date: 03-09-2001
DOI: 10.1002/1521-3765(20010903)7:17<3756::AID-CHEM3756>3.0.CO;2-Q
Abstract: Combined low temperature (28(1) K) X-ray and neutron diffraction measurements were carried out on the co-crystallised complex of betaine, imidazole, and picric acid (1). The experimental charge density was determined and compared with ab initio theoretical calculations at the B3LYP/6-311G(d,p) level of theory. The complex serves as a model for the active site in, for ex le, the serine protease class of enzymes, the so-called catalytic triad. The crystal contains three short strong N-H...O hydrogen bonds (HBs) with dN...O < 2.7 A. The three HBs have energies above 13 kcalmol(-1), although the hydrogen atoms are firmly localized in the "nitrogen wells". This suggests that low-barrier hydrogen bonding in catalytic enzyme reactions may be a sufficient, but not a necessary, condition for obtaining transition-state stabilization. Structural analysis (e.g., covalent N-H bond lengthening) indicates that the hydrogen bond between H3A and 08 of imidazole and betaine respectively (HB2) is slightly stronger than the bond between H1A and O1A of imidazole and picric acid (HB1), although HB1 is shorter than HB2: (dN...O(HB1)= 2.614(1) A, dN...O(HB2) = 2.684(1) A, dH...O(HB1) = 1.630(1) A, dH...O(HB2)= 1.635(1) A, dN-H(HB1) = 1.046(1) A, dN-H(HB2) = 1.057(1) A). Furthermore, the charge density analysis reveals that HB2 has a larger covalent character than HB1, with considerable polarization of the density towards the acceptor atom. The Gatti and Bader source function (S) is introduced to the analysis of strong HBs. The source function is found to be a sensitive measure for the nature of a hydrogen bond, and comparison with low-barrier and single-well hydrogen bonding systems (e.g., benzoylacetone and nitromalonamide) shows that the low-barrier hydrogen bond (LBHB) state is characterized by an enormously increased hydrogen atom source contribution to the bond critical point in the HB. In this context, HB2 can be characterized as intermediate between localized HBs and delocalized LBHBs.
Publisher: International Union of Crystallography (IUCr)
Date: 30-08-2008
DOI: 10.1107/S0021889808024643
Abstract: A 165 mm Mar CCD detector has been fitted on a large Huber four-circle diffractometer together with a helium cryostat at beamline D3 at Hasylab, DESY in Hamburg. This setup allows fast collection of accurate, short-wavelength, very low temperature X-ray diffraction data for charge-density analysis. As a test ex le, diffraction data have been collected in 10 h on a hydrogen-bonded network system with 15 unique atoms, and the electron density was modelled with the multipole formalism in an X–N procedure using matching-temperature neutron diffraction data collected at Institut Laue Langevin, Grenoble in France.
Publisher: International Union of Crystallography (IUCr)
Date: 31-05-2014
DOI: 10.1107/S2052520614003497
Abstract: Ionothermal reaction between Mn II (acetate) 2 ·4H 2 O and 1,3,5-benzenetricarboxylic acid (H 3 BTC) in either of the two ionic liquids 1-ethyl-3-methylimidazolium bromide (EMIMBr) and 1-ethyl-3-methylimidazolium tosylate (EMIMOTs) resulted in the formation of the new metal–organic framework (MOF) EMIM[Mn II BTC] (BTC = 1,3,5-benzenetricarboxylate). The compound crystallizes in the orthorhombic space group Pbca with unit-cell parameters of a = 14.66658 (12), b = 12.39497 (9), c = 16.63509 (14) Å at 100 K. Multi-temperature single-crystal (15–340 K) and powder X-ray diffraction studies (100–400 K) reveal strongly anisotropic thermal expansion properties. The linear thermal expansion coefficients, α L ( l ), attain maximum values at 400 K along the a - and b -axis, with α L ( a ) = 115 × 10 −6 K −1 and α L ( b ) = 75 × 10 −6 K −1 . At 400 K a negative thermal expansion coefficient of −40 × 10 −6 K −1 is observed along the c -axis. The thermal expansion is coupled to a continuous deformation of the framework, which causes the structure to expand in two directions. Due to the rigidity of the linker, the expansion in the ab plane causes the network to contract along the c -axis. Hirshfeld surface analysis has been used to describe the interaction between the framework structure and the EMIM cation that resides within the channel. This reveals a number of rather weak interactions and one governing hydrogen-bonding interactions.
Publisher: International Union of Crystallography (IUCr)
Date: 02-2016
DOI: 10.1107/S1600576715022621
Abstract: A serious limitation of the all-in-vacuum diffractometer reported by Straasø, Dippel, Becker & Als-Nielsen [ J. Synchrotron Rad. (2014), 21 , 119–126] has so far been the inability to cool s les to near-cryogenic temperatures during measurement. The problem is solved by placing the s le in a jet of helium gas cooled by liquid nitrogen. The resulting temperature change is quantified by determining the change in unit-cell parameter and atomic displacement parameter of copper. The cooling proved successful, with a resulting temperature of ∼95 (3) K. The measured powder X-ray diffraction data are of superb quality and high resolution [up to sinθ/λ = 2.2 Å −1 ], permitting an extensive modelling of the thermal displacement. The anharmonic displacement of copper was modelled by a Gram–Charlier expansion of the temperature factor. As expected, the corresponding probability distribution function shows an increased probability away from neighbouring atoms and a decreased probability towards them.
Publisher: International Union of Crystallography (IUCr)
Date: 26-08-2004
DOI: 10.1107/S010876730401699X
Abstract: A new magnetic metal-organic framework material, [Mn 2 (C 8 OH 4 4 ) 2 (C 3 H 7 NO) 2 ], has been synthesized. The structure consists of chains of carboxylate-bridged Mn atoms interconnected with acid linkers, giving much larger interchain than intrachain Mn...Mn distances. Magnetic susceptibility data fitted to a Curie–Weiss law give Θ = −5.7 K and a total magnetic moment of 5.96 µ B . The heat capacity provides no evidence of magnetic ordering down to 2 K. The X-ray charge density was determined from multipole modeling of 16 (1) K single-crystal synchrotron-radiation data. The structural surroundings of the two unique Mn centers are different, but orbital population analysis reveals close to single electron occupation in all 3 d orbitals of both Mn sites, in agreement with the magnetic susceptibility measurements. Bader topological analysis shows the presence of direct chemical Mn...Mn interactions only in two out of three intrachain contacts, which suggests a `broken' chain. The topological measures and approximate energy densities at the metal–ligand bond critical points (ρ, ∇ 2 ρ, G , V and H ) indicate ionic interactions. Formal electron counting suggests mixed-valence Mn sites, but this hypothesis is not supported by the Bader atomic charges [ q (Mn) = +2.035 and +2.031].
Publisher: Elsevier BV
Date: 10-2010
Publisher: Elsevier BV
Date: 12-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3DT52035H
Abstract: Single crystal X-ray diffraction studies of the symmetrical molecular wire compound Co3(dpa)4Cl2·(dcm) have been performed up to a pressure of 3.6 GPa using both synchrotron and conventional sources. It is found that the terminal Co-Cl bond distance initially increases by 0.013(4) Å at 0.32 GPa after which it continuously decreases. Extensive theoretical calculations show that population of a thermally excited state containing increased Co-Cl anti-bonding character is a possibility at 0.32 GPa. The relative occupancy of the disordered dcm solvent molecule changes significantly with pressure and this is explained by the analysis of void spaces and Hirshfeld surfaces at different pressures. At 3.2 GPa, fingerprint plots derived from Hirshfeld surfaces indicate that neighbouring metal chain compounds approach each other such that short H···H interactions appear.
Publisher: American Physical Society (APS)
Date: 22-03-2013
Publisher: American Physical Society (APS)
Date: 16-08-2011
Publisher: American Chemical Society (ACS)
Date: 06-2005
DOI: 10.1021/JA051233Z
Abstract: A new magnetic metal organic framework material has been synthesized, Mn3(C8O4H4)3(C5H11ON)2, 1. Magnetic susceptibility measurements from 2 to 400 K reveal anti-ferromagnetic ordering at approximately 4 K and a total magnetic moment of 6.0 micro(B). The magnetic phase transition is confirmed by heat capacity data (2-300 K). The crystal structure is studied by conventional single-crystal X-ray diffraction data at 300, 275, 250, 225, 200, 175, 150, 125, and 100 K, and synchrotron data at 20 K. There is a phase transition between 100 and 20 K due to ordering of the diethylformamide molecules. The X-ray charge density is determined based on multipole modeling of a second 20 K single-crystal synchrotron radiation data set. The electron distributions around the two unique Mn centers are different, and both have substantial anisotropy. Orbital population analysis reveals large electron donation (1.7 e) to each Mn atom and the maximum possible number of unpaired electrons is 3.2 for both Mn sites. Thus, there is a considerable orbital component to the magnetic moment. Bader topological analysis shows an absence of Mn-Mn bonding, and the magnetic ordering is via super-exchange through the oxygen bridges. Formal electron counting suggests Mn2+ sites, but this is not supported by the Bader atomic charges, Mn1 = +0.11 e, Mn2 = +0.17 e. The topological measures show the dominant metal-ligand interactions to be electrostatic, and a simple exponential correlation is derived between Mn-O bond lengths and the values of nabla2rho at the bond critical points.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0CC06795D
Abstract: A simple method has been developed for synthesis of phase-pure and highly crystalline brookite TiO 2 nanoparticles from a broad range of titanium precursors.
Publisher: IEEE
Date: 2006
Publisher: Wiley
Date: 19-07-2016
Publisher: Springer Science and Business Media LLC
Date: 17-07-2019
DOI: 10.1038/S41524-019-0215-Y
Abstract: Over the past two decades, we have witnessed a strong interest in developing Mg 3 Sb 2 and related CaAl 2 Si 2 -type materials for low- and intermediate-temperature thermoelectric applications. In this review, we discuss how computations coupled with experiments provide insights for understanding chemical bonding, electronic transport, point defects, thermal transport, and transport anisotropy in these materials. Based on the underlying insights, we examine design strategies to guide the further optimization and development of thermoelectric Mg 3 Sb 2 -based materials and their analogs. We begin with a general introduction of the Zintl concept for understanding bonding and properties and then reveal the breakdown of this concept in AMg 2 X 2 with a nearly isotropic three-dimensional chemical bonding network. For electronic transport, we start from a simple yet powerful atomic orbital scheme of tuning orbital degeneracy for optimizing p-type electrical properties, then discuss the complex Fermi surface aided by high valley degeneracy, carrier pocket anisotropy, and light conductivity effective mass responsible for the exceptional n-type transport properties, and finally address the defect-controlled carrier density in relation to the electronegativity and bonding character. Regarding thermal transport, we discuss the insight into the origin of the intrinsically low lattice thermal conductivity in Mg 3 Sb 2 . Furthermore, the anisotropies in electronic and thermal transport properties are discussed in relation to crystal orbitals and chemical bonding. Finally, some specific challenges and perspectives on how to make further developments are presented.
Publisher: American Chemical Society (ACS)
Date: 26-07-2019
Publisher: American Physical Society (APS)
Date: 17-07-2013
Publisher: Elsevier BV
Date: 07-2016
Publisher: American Chemical Society (ACS)
Date: 06-03-2023
Publisher: Wiley
Date: 14-02-2023
Abstract: Loosely bonded (“rattling”) atoms with s 2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X‐ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low‐lying transverse phonons dominated by large In 1+ z‐ axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In 1+ 5 s 2 lone pair electrons and Te 5 p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion.
Publisher: American Chemical Society (ACS)
Date: 18-08-2015
Publisher: American Chemical Society (ACS)
Date: 06-2017
Publisher: International Union of Crystallography (IUCr)
Date: 27-07-2017
DOI: 10.1107/S2052520617006357
Abstract: In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the s le-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole–Rietveld procedure and compared with ab initio calculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: AIP Publishing
Date: 2009
DOI: 10.1063/1.3037203
Abstract: Cation doping studies of high performance thermoelectric Zn4Sb3 have so far focused on elements with larger electronegativity than Zn. Mg has a lower electronegativity than Zn, and, in the present paper, the effect of Mg doping of Zn4Sb3 on phase transition temperatures and thermal and thermoelectric properties have been studied on five s les with a doping degree ranging from 0.1 to 2 at. % Mg. The results are compared with data obtained for a pure, undoped s le. Laboratory x-ray powder diffraction shows that all s les are single phase materials as further evidenced with higher confidence by Rietveld refinement of high resolution synchrotron powder diffraction of as synthesized 1 and 2 at. % Mg doped s les. Multitemperature synchrotron powder diffraction and differential scanning calorimetry reveal a significant effect of Mg-doping on the low temperature phase transitions in one s le (0.5 at. % Mg), whereas the other s les showed only small or no effect. Physical properties have been evaluated from 2–400 K for all s les. Some physical property parameters are affected by doping but no immediate improvement of ZT was achieved. The reason for this is discussed in relation to differences in s le compaction.
Publisher: American Physical Society (APS)
Date: 29-11-2010
Publisher: International Union of Crystallography (IUCr)
Date: 13-05-2016
DOI: 10.1107/S2052520616003334
Abstract: Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram–Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.
Publisher: American Chemical Society (ACS)
Date: 16-06-2017
Publisher: American Physical Society (APS)
Date: 28-12-2007
Publisher: IEEE
Date: 08-2006
Publisher: Springer Science and Business Media LLC
Date: 31-08-2008
DOI: 10.1038/NMAT2273
Abstract: Engineering of materials with specific physical properties has recently focused on the effect of nano-sized 'guest domains' in a 'host matrix' that enable tuning of electrical, mechanical, photo-optical or thermal properties. A low thermal conductivity is a prerequisite for obtaining effective thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the 'phonon glass-electron crystal' concept and may be realized in host-guest systems. The guest entities are believed to have independent oscillations, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass-electron crystal material Ba(8)Ga(16)Ge(30) using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically predicted avoided crossing of the rattler modes and the acoustic-phonon branches. The observed phonon lifetimes are longer than expected, and a new explanation for the low kappa(L) is provided.
Publisher: American Chemical Society (ACS)
Date: 13-05-2009
DOI: 10.1021/JA8091032
Abstract: Depending on the number of interstitial solvent molecules, n, crystals of the linear chain compound Co(3)(dipyridylamide)(4)Cl(2) x nCH(2)Cl(2) adopt either symmetrical or unsymmetrical metal chain structures. We explore here the possible reasons for such behavior using Hirshfeld surface analysis of intermolecular interactions as well as the charge density determined from 100(1) K X-ray diffraction data on the unsymmetrical complex Co(3)(dipyridylamide)(4)Cl(2) x 2.11 CH(2)Cl(2), u-1, and crystal structures of u-1 determined from single crystal synchrotron X-ray diffraction data at 20, 150, and 300 K. The new crystal structures are compared with previous structural results on a crystal with slightly different solvent content. This change in solvent content only affects the bond distances to atom Co(3), which are also strongly affected by temperature changes due to a spin crossover transition. Large differences in intermolecular interactions are revealed by the Hirshfeld surface analysis between symmetrical (s-1) and unsymmetrical (u-1) crystal solvates, suggesting that the molecular isomerism is strongly influenced by crystal packing effects. Topological analysis of the static electron density of u-1 suggests that there is direct metal-metal bonding for both the shorter Co(1)-Co(2) and the longer Co(2)-Co(3) contact. The approximate description of the system as a (Co(2))(2+)-dimer and an isolated Co(2+)-ion is reflected in the character of the metal-ligand interactions, which are more ionic for the isolated Co(3) atom, and the topological charges Co(1)(+0.50), Co(2)(+0.77), and Co(3)(+1.36). The two termini of u-1 are found to be very different, both in terms of structural surroundings as well as topology. The central Co(2) atom is similar to a cobalt atom in a tetragonally distorted octahedral environment resulting in preferred occupancy in the t(2g) orbitals. The Co(1) atom has significant deformation in the xz and yz planes (z along the chain axis, x and y toward ligands) reflecting covalent interactions with the terminal chlorine atom Cl(1). The Co(3) atom has a relatively high occupancy of the d(x(2)-y(2)) orbital and a relatively low occupancy of the d(xy) orbital confirming that these orbitals are involved in the spin crossover process and predominantly responsible for the observed variation in bond lengths with temperature.
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B810783A
Publisher: Wiley
Date: 28-05-2013
Publisher: International Union of Crystallography (IUCr)
Date: 19-06-2019
DOI: 10.1107/S2052520619005791
Abstract: Carbon nitride materials include functional materials, and their chemical ersity and complexity are becoming increasingly appreciated. Heating of NH 4 SCN leads to a range of new carbon nitride compounds, which have been structurally characterized by single-crystal X-ray diffraction. Heating at ambient pressure to 175°C leads to guanidinium thiocyanate, H 6 CN 3 SCN ( 1 ), and when maintaining that temperature for about 12 h a water-insoluble carbon nitride product is formed, which is a co-crystal between melamine and melamium thiocyanate, [H 6 C 3 N 6 ]·[H 10 C 6 N 11 ] + ·[SCN] − ( 2 ). In situ powder X-ray diffraction measurements of this material reveal a gradual transformation from ( 2 ), via two intermediate products, to a final melon-like end product. The first of these forms between 350 and 400°C, and is an adduct of melam and melamium thiocyanate, [H 9 C 6 N 11 ]·2[H 10 C 6 N 11 ] + ·2[SCN] − ( 3 ). The second forms between 400 and 480°C, and is identified as melem, 2,5,8-triamino-tri- s -triazine, H 6 C 6 N 10 ( 4 ). On heating of ( 2 ) in a sealed oule to 600°C, various crystals were obtained and six crystal structures were determined from the batch: 1,3,5-triazine-2,4,6-triamino, H 6 C 3 N 6 ( 5 ), 1,3,5-triazine-2,4-diamino, H 5 C 3 N 5 ( 6 ), 1,1′,3,3′,5,5′-triazine-2,2′,4,4′-tetraamino, H 8 C 6 N 10 ( 7 ), 2[H 6 C 3 N 6 ]·[H 10 C 6 N 11 ] + ·[SCN] − ( 8 ) and 2[H 6 C 3 N 6 ]·[H 7 C 3 N 6 ] + ·[SCN] − ( 9 ). Finally, a recrystallized decomposition product was found to be [H 6 C 3 N 6 ]·[H 7 C 3 N 6 ] + ·[SCN] − ·[H 2 O] ( 10 ).
Publisher: International Union of Crystallography (IUCr)
Date: 14-04-2014
DOI: 10.1107/S2052252514006538
Abstract: Understanding the mechanism of nanoparticle formation during synthesis is a key prerequisite for the rational design and engineering of desirable materials properties, yet remains elusive due to the difficulty of studying structures at the nanoscale under real conditions. Here, the first comprehensive structural description of the formation of a nanoparticle, yttria-stabilized zirconia (YSZ), all the way from its ionic constituents in solution to the final crystal, is presented. The transformation is a complicated multi-step sequence of atomic reorganizations as the material follows the reaction pathway towards the equilibrium product. Prior to nanoparticle nucleation, reagents reorganize into polymeric species whose structure is incompatible with the final product. Instead of direct nucleation of clusters into the final product lattice, a highly disordered intermediate precipitate forms with a local bonding environment similar to the product yet lacking the correct topology. During maturation, bond reforming occurs by nucleation and growth of distinct domains within the amorphous intermediary. The present study moves beyond kinetic modeling by providing detailed real-time structural insight, and it is demonstrated that YSZ nanoparticle formation and growth is a more complex chemical process than accounted for in conventional models. This level of mechanistic understanding of the nanoparticle formation is the first step towards more rational control over nanoparticle synthesis through control of both solution precursors and reaction intermediaries.
Publisher: Wiley
Date: 16-01-2020
Abstract: Precursor structures (PSs) in solution are expected to influence both nanocrystal formation mechanisms, as well as crystallization of specific polymorphs. Herein, Group 13 PS structures determined by pair distribution function and extended X-ray absorption fine structure analysis are reported. Corner-sharing octahedral dimers form from the metal nitrates dissolved in either water, isopropanol, or ethanol at room temperature contradicting previous studies that suggested monomers or larger Keggin clusters. Because all crystalline indium oxides have octahedral coordination, crystals can easily nucleate from the observed PSs. Similarly, MOOH (M=Al and Ga) with octahedral M coordination is expected to form readily from the PSs, whereas formation of γ-M
Publisher: Elsevier BV
Date: 05-2011
Publisher: IEEE
Date: 2006
Publisher: American Chemical Society (ACS)
Date: 05-02-2014
DOI: 10.1021/CG4018129
Publisher: American Physical Society (APS)
Date: 28-08-2007
Publisher: AIP Publishing
Date: 08-2009
DOI: 10.1063/1.3155800
Abstract: Highly textured FeSb2 films were produced on quartz wafers by a sputtering method. Their resistivity and Seebeck coefficient (S) were measured and a maximum absolute value of S∼160 μV K−1 at 50 K was obtained. Hall measurements were employed to study the charge carrier concentrations and Hall mobilities of the FeSb2 films. By comparing with the transport properties of FeSb2 single crystals and an extrinsically doped FeSb1.98Te0.02 single crystal, the thermoelectric properties of the FeSb2 films are demonstrated to be dominated by the intrinsic properties of FeSb2 at a high charge carrier concentration.
Publisher: Wiley
Date: 26-08-2011
Abstract: FeSb 2 has been recently identified as a new model system for studying many‐body renormalizations in a d‐electron based narrow gap semiconducting system, strongly resembling FeSi. The electron‐electron correlations in FeSb 2 manifest themselves in a wide variety of physical properties including electrical and thermal transport, optical conductivity, magnetic susceptibility, specific heat and so on. We review some of the properties that form a set of experimental evidences revealing a significant role of correlation effects in FeSb 2 . The metallic state derived from slight Te doping in FeSb 2 , which exhibits a large quasiparticle mass, will also be introduced.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3NR33127J
Abstract: A new step in supercritical nanoparticle synthesis, the pulsed supercritical synthesis reactor, is investigated in situ using synchrotron powder X-ray diffraction (PXRD) to understand the formation of nanoparticles in real time. This eliminates the common problem of transferring information gained during in situ studies to subsequent laboratory reactor conditions. As a proof of principle, anatase titania nanoparticles were synthesized in a 50/50 mixture of water and isopropanol near and above the critical point of water (P = 250 bar, T = 300, 350, 400, 450, 500 and 550 °C). The evolution of the reaction product was followed by sequentially recording PXRD patterns with a time resolution of less than two seconds. The crystallite size of titania is found to depend on both temperature and residence time, and increasing either parameter leads to larger crystallites. A simple adjustment of either temperature or residence time provides a direct method for gram scale production of anatase nanoparticles of average crystallite sizes between 7 and 35 nm, thus giving the option of synthesizing tailor-made nanoparticles. Modeling of the in situ growth curves using an Avrami growth model gave an activation energy of 66(19) kJ mol(-1) for the initial crystallization. The in situ PXRD data also provide direct information about the size dependent macrostrain in the nanoparticles and with decreasing crystallite size the unit cell contracts, especially along the c-direction. This agrees well with previous ex situ results obtained for hydrothermal synthesis of titania nanoparticles.
Publisher: Wiley
Date: 21-06-2011
Publisher: International Union of Crystallography (IUCr)
Date: 23-04-2005
Publisher: Wiley
Date: 28-09-2023
Publisher: American Chemical Society (ACS)
Date: 14-09-2016
Abstract: Rubrene endoperoxide p-xylene (1) has been obtained in crystalline form from recrystallization and purification of the organic semiconductor, rubrene, and for the first time characterized by single-crystal X-ray diffraction methods. 1 is produced by reaction of rubrene with molecular oxygen to create rubrene endoperoxide, C42H28O2, in which an O2-bridge is joining the two phenyl-substituted C atoms opposite each other in the second of the four aromatic rings in tetracene thereby breaking the resonance along the tetracene moiety. The electron density distribution of 1 reveals that the intramolecular O-O bond is best characterized as charge-shift bonding with loss of electronic concentration in the interatomic region evidenced by the Laplacian. Likewise the ELI-D indicates little electron localization in this region. Furthermore, source function and ELI-D analysis of 1 clearly quantifies the lack of electronic delocalization across the six-membered ring that carries the peroxide-bridge.
Publisher: American Physical Society (APS)
Date: 31-03-2014
Publisher: American Chemical Society (ACS)
Date: 23-02-2021
Publisher: AIP Publishing
Date: 21-04-2008
DOI: 10.1063/1.2916705
Abstract: The thermal stability of thermoelectric Zn4Sb3 has been investigated on s les produced by a new zone-melting technique, as well as by the conventional quench method. The multitemperature synchrotron powder diffraction data reveal that while conventionally synthesized, Zn4Sb3 s les have almost 40% degradation in the first heating cycle at 625K, s les prepared by zone melting only have 3% degradation. Repeated thermal cycling induces additional degradation of the quenched s le of up to 58%, compared to ∼9% degradation in the zone-melted s le. Thus, zone-melting produces Zn4Sb3 s les that are significantly more thermally stable, which make them promising for commercial implementation.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B916400F
Abstract: Thermoelectric clathrates hold significant promise for high temperature applications with zT values exceeding 1.3. The inorganic clathrates have been shown to be both chemically and thermally stable at high temperatures, and high performance can be obtained from both single crystals and processed powders. The clathrates also show excellent compatibility factors in segmented module applications. For a materials chemist it is furthermore of great importance that the clathrates exhibit a very rich chemistry with the ability for substitution of many different elements. This allows delicate tuning of both the crystal structure as well as the physical properties. With all these assets, it is not surprising that clathrates have been intensely investigated in the thermoelectric community during the past decade. The present perspective provides a review of the many studies concerned with the synthesis, crystal structure and thermoelectric properties of clathrates with emphasis on the type I clathrate.
Publisher: International Union of Crystallography (IUCr)
Date: 30-07-2021
DOI: 10.1107/S1600576721006294
Abstract: Operando characterization provides direct insight into material response under application conditions and it is essential to understand the stability limits of thermoelectric materials and their decomposition mechanisms. An operando setup capable of maintaining a thermal gradient while running DC current through a bar-shaped s le has been developed. Under operating conditions, X-ray scattering data can be measured along the s le to obtain spatially resolved structural knowledge in concert with measurement of electrical resistance and the Seebeck coefficient. Here thermoelectric β-Zn 4 Sb 3 , which is a mixed ionic–electronic conductor, is studied, and a significant temperature dependence of the Zn migration is directly observed. Measurements with the thermal gradient applied either along or opposite to the DC current establish that the ion migration is an electrochemical effect rather than a thermodiffusion. Consideration of only the applied critical voltage or current density is insufficient for deducing the stability limits and structural integrity of materials with temperature-dependent ion mobility. The present operando setup is not limited to studies of thermoelectric materials, and it also lends itself to studies of, for ex le, ion diffusion in solid-state electrolytes or structural transformations in solid-state reactions.
Publisher: American Chemical Society (ACS)
Date: 14-01-2010
DOI: 10.1021/CM903316S
Publisher: IEEE
Date: 06-2007
Publisher: Springer Science and Business Media LLC
Date: 25-06-2015
DOI: 10.1038/NCOMMS8475
Abstract: The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb 3 , where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.
Publisher: AIP Publishing
Date: 27-11-2002
DOI: 10.1063/1.1519334
Abstract: Zone melting purification experiments have been carried out on the clathrate, Ba8Ga16Ge30. The impurities present have been identified and their approximate concentrations measured. Trace impurities were determined to be approximately 240 parts per million (ppm) in the most impure s le to 17 ppm in the most pure s le. The temperature-dependent Seebeck coefficient, thermal conductivity, and electrical conductivity are reported as a function of s le purity as well as the room-temperature Hall coefficient. Microprobe analysis suggests that the s les are nonstoichiometric with excess Ge relative to Ga, and there are indications of the presence of defects. Single-crystal x-ray investigations as well as synchrotron powder diffraction measurements support the presence of defects, but the x-ray data cannot accurately determine the relative amounts of Ga and Ge. Band-structure calculations in the generalized gradient approximation show that the measured Hall and Seebeck coefficients are consistent with a defect lattice of approximate stoichiometry Ba8Ga14Ge31. Although the figure of merit (ZT) is found to be the highest for the purest s le, the dominant contribution to transport is conjectured to arise from deviations from the ideal stoichiometry and not impurities.
Publisher: American Chemical Society (ACS)
Date: 19-01-2016
Publisher: American Chemical Society (ACS)
Date: 19-06-2017
Publisher: American Physical Society (APS)
Date: 15-01-2000
Publisher: AIP Publishing
Date: 10-2014
DOI: 10.1063/1.4896198
Abstract: An electrochemical cell has been designed for powder X-ray diffraction studies of lithium ion batteries (LIB) and sodium ion batteries (SIB) in operando with high time resolution using a conventional powder X-ray diffractometer. The cell allows for studies of both anode and cathode electrode materials in reflection mode. The cell design closely mimics that of standard battery testing coin cells and allows obtaining powder X-ray diffraction patterns under representative electrochemical conditions. In addition, the cell uses graphite as the X-ray window instead of beryllium, and it is easy to operate and maintain. Test ex les on lithium insertion/extraction in two spinel-type LIB electrode materials (Li4Ti5O12 anode and LiMn2O4 cathode) are presented as well as first results on sodium extraction from a layered SIB cathode material (Na0.84Fe0.56Mn0.44O2).
Publisher: International Union of Crystallography (IUCr)
Date: 08-08-1996
Publisher: International Union of Crystallography (IUCr)
Date: 15-01-2005
Publisher: Springer Science and Business Media LLC
Date: 2011
Abstract: Compaction of β-Zn 4 Sb 3 was carried out by current-assisted short term sintering under pressure (STS) using different material and process parameters. Surface Seebeck mapping (PSM) of the compacted specimens (along the uniaxial pressing direction) shows a wide gradation ranging from ∼40–180 μV/K due to electro-migration of Zinc along the current direction. The wide distribution of S corresponds to a mixture of Zn-Sb phases [1] which arise depending on the extent of Zinc migration during the STS process. Variation in the material and process parameters (average particle size, heating rate, compaction time/temperature) results in different spatial distribution of S. Measurements of electrical (σ), thermal (κ) conductivities and Seebeck (S) coefficients between room temperature and 523 K were carried out on two specimens having different average S values and distributions as observed by the PSM. The results indicate an increase in the lattice thermal conductivity (κ L ) and subsequent lower ZT in the specimens compared to the reported values for β-Zn 4 Sb 3 .
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C2DT31491F
Abstract: Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn(4)O(1,4-benzenedicarboxylate)(3)). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder- and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the s le and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be d ened by applying a gas pressure to the s le. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature.
Publisher: Wiley
Date: 06-10-2011
Publisher: International Union of Crystallography (IUCr)
Date: 05-07-2015
DOI: 10.1107/S2052252515012221
Abstract: By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The `tfPDF' method is illustrated through studies of as-deposited ( i.e. amorphous) and crystalline FeSb 3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb 3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb 3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb 6 octahedra with motifs highly resembling the local structure in crystalline FeSb 3 . Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb 3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.
Publisher: Elsevier BV
Date: 02-2000
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2DT02128E
Abstract: Variations in the crystal structure and bond lengths of three anatase TiO 2 s les with average crystallite sizes of 6 nm, 19 nm and several hundred nm, respectively, are due to hydroxyl defects rather than nanosize effects.
Publisher: International Union of Crystallography (IUCr)
Date: 15-10-2005
Publisher: American Chemical Society (ACS)
Date: 20-12-2022
Publisher: International Union of Crystallography (IUCr)
Date: 19-05-2010
Publisher: Kluwer Academic Publishers
Publisher: International Union of Crystallography (IUCr)
Date: 13-04-2021
DOI: 10.1107/S2052252521002852
Abstract: Zinc antimonides have been widely studied owing to their outstanding thermoelectric properties. Unlike in the bulk state, where various structurally unknown phases have been identified through their specific physical properties, a number of intermediate phases in the thin-film state remain largely unexplored. Here, in situ X-ray diffraction and X-ray total scattering are combined with in situ measurement of electrical resistivity to monitor the crystallization process of as-deposited amorphous Zn-Sb films during post-deposition annealing. The as-deposited Zn-Sb films undergo a structural evolution from an amorphous phase to an intermediate crystalline phase and finally the ZnSb phase during heat treatment up to 573 K. An intermediate phase (phase B) is identified to be a modified β-Zn 8 Sb 7 phase by refinement of the X-ray diffraction data. Within a certain range of Sb content (∼42–55 at%) in the films, phase B is accompanied by an emerging Sb impurity phase. Lower Sb content leads to smaller amounts of Sb impurity and the formation of phase B at lower temperatures, and phase B is stable at room temperature if the annealing temperature is controlled. Pair distribution function analysis of the amorphous phase shows local ordered units of distorted ZnSb 4 tetrahedra, and annealing leads to long-range ordering of these units to form the intermediate phase. A higher formation energy is required when the intermediate phase evolves into the ZnSb phase with a significantly more regular arrangement of ZnSb 4 tetrahedra.
Publisher: The Crystallographic Society of Japan
Date: 2005
DOI: 10.5940/JCRSJ.47.204
Publisher: Elsevier BV
Date: 08-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B811576A
Abstract: The experimental electron density distribution in a crystal consisting of the simplest conceivable trinuclear carboxylate-bridged iron-mu3-oxo dianion with two alpha-picolinium cations has been determined using both synchrotron (15 K) and conventional (100 K) X-ray diffraction data. The constituent trinuclear oxo-centered molecule consists of six mu2-bridging formate groups between the iron pairs, while the axial ligand for all iron atoms is another formate group. The compound {[FeO(HCOO)5(HCOO)3]2-.H2O.2(alpha-CH3NC5H5)}, (1) crystallizes in the monoclinic space group P2(1)/m with charge assisted hydrogen bonds linking the alpha-picolinium cations to the trinuclear groups. The chemical bonding in the weakly asymmetric Fe3O-core of 1 has been examined through the use of the quantum theory of atoms in molecules, and in combination with experimental d-orbital populations, a significant electron sharing is observed between the Fe atoms and the central oxygen. The central oxygen exhibits clear sp2 hybridization, and the iron atoms have valence shell charge concentrations in all metal-ligand bond directions. The relative bond strengths are evaluated based upon the charge density distribution and found to be in accordance with the geometrical results. Integrated group charges follow expectations from formal chemical valences.
Publisher: Elsevier BV
Date: 03-2009
Publisher: American Physical Society (APS)
Date: 03-02-2014
Publisher: Wiley
Date: 29-03-2022
Abstract: Glass‐forming metal–organic frameworks (MOFs) have novel applications, but the origin of their peculiar melting behavior is unclear. Here, we report synchrotron X‐ray diffraction electron densities of two zeolitic imidazolate frameworks (ZIFs), the glass‐forming Zn‐ZIF‐zni and the isostructural thermally decomposing Co‐ZIF‐zni. Electron density analysis shows that the Zn−N bonds are more ionic than the Co−N bonds, which have distinct covalent features. Variable‐temperature Raman spectra reveal the onset of significant imidazolate bond weakening in Co‐ZIF‐zni above 673 K. Melting can be controlled by tuning the metal–ligand and imidazole bonding strength as shown from thermal analysis of nine solid‐solution Co x Zn 1− x ‐ZIF‐zni ( x =0.3 to 0.003) MOFs, and a mere 4 % Co‐doping into Zn‐ZIF‐zni results in thermal decomposition instead of melting. The present findings demonstrate the key role of the metal–ligand bonds and imidazolate bonds in controlling the delicate balance between melting and decomposition processes in this class of ZIF compounds.
Publisher: American Chemical Society (ACS)
Date: 22-10-2013
DOI: 10.1021/CG400858P
Publisher: American Chemical Society (ACS)
Date: 16-09-2010
DOI: 10.1021/IC100990A
Abstract: The hexagonal polymorph of CeMnNi(4) has been synthesized using cold crucible, high-frequency induction melting with subsequent Czochralski crystal pulling. Single-crystal X-ray diffraction, multitemperature synchrotron powder X-ray diffraction (90 to 600 K), and neutron powder diffraction data have been measured to establish the detailed crystal structure and in particular the location of the Mn atoms. The neutron diffraction data provide sufficient scattering contrast between Mn and Ni to establish that the 2c site has an occupancy of 13% Mn atoms, while the 3g site has an occupancy of 25% Mn atoms. Thus, the crystal structure is complex with considerable disorder. Rietveld refinement of the multitemperature synchrotron data establishes a near linear thermal expansion coefficient of 13.9(3) × 10(-6) K(-1) and 14.9(3) × 10(-6) K(-1) for the a and c axes, respectively. Atomic Hirshfeld surfaces are introduced as a new tool to investigate the atomic coordination and interactions in intermetallic compounds. The atomic displacement parameters (ADPs) are observed to be much larger for the heavy Ce atom than for the lighter Mn and Ni atoms, and this correlates with the large atomic Hirshfeld volume of Ce relative to Mn and Ni. The fit of a Debye model to the ADPs gives θ(D) = 312(3) K. Magnetic susceptibility data measured between 2 and 350 K indicate ferromagnetic ordering at 122(2) K (Weiss constant) based on a linear fit of the inverse magnetic susceptibility in the paramagnetic region. Transport properties were measured on a polycrystalline s le containing CeO(2) (2.8%) and Ni (7.7%) impurities. The electrical conductivity is observed to be metallic with a distinct kink in the data around 120 K coinciding with the observed Curie temperature. The lattice thermal conductivity (κ(L)) increases from 0.5 W/Km at 2 K to 8 W/Km at 50 K, and the relatively moderate value of κ(L) probably reflects the significant structural disorder.
Publisher: Wiley
Date: 02-10-2013
Abstract: The understanding of lithium-ion migration through the bulk crystal structure is crucial in the search for novel battery materials with improved properties for lithium-ion conduction. In this paper, procrystal calculations are introduced as a fast, intuitive way of mapping possible migration pathways, and the method is applied to a broad range of lithium-containing materials, including the well-known battery cathode materials LiCoO2 , LiMn2 O4 , and LiFePO4 . The outcome is compared with both experimental and theoretical studies, as well as the bond valence site energy approach, and the results show that the method is not only a strong, qualitative visualization tool, but also provides a quantitative measure of electron-density thresholds for migration, which are correlated with theoretically obtained activation energies. In the future, the method may be used to guide experimental and theoretical research towards materials with potentially high ionic conductivity, reducing the time spent investigating nonpromising materials with advanced theoretical methods.
Publisher: Elsevier BV
Date: 12-2017
Publisher: American Physical Society (APS)
Date: 13-01-2014
Publisher: American Physical Society (APS)
Date: 07-11-2006
Publisher: American Chemical Society (ACS)
Date: 06-07-2015
Publisher: American Chemical Society (ACS)
Date: 08-10-2020
Publisher: Springer Science and Business Media LLC
Date: 26-10-2012
Publisher: Elsevier BV
Date: 05-2013
Publisher: Springer Science and Business Media LLC
Date: 27-06-2004
DOI: 10.1038/NMAT1154
Publisher: American Chemical Society (ACS)
Date: 18-09-1999
DOI: 10.1021/CM9910658
Publisher: American Chemical Society (ACS)
Date: 13-04-2016
Publisher: International Union of Crystallography (IUCr)
Date: 26-05-2016
DOI: 10.1107/S2052520616005515
Abstract: The effect of pressure on the crystal structure of a coordination polymer, emim[Mn II (btc)] (emim = 1-ethyl,3-methyl imidazolium cation, btc = 1,3,5-benzene-tricarboxylate), was investigated with single-crystal X-ray diffraction. At 4.3 GPa the unit-cell volume had decreased by 14% compared with ambient conditions. The unit-cell contraction is highly anisotropic, with the a - and b -axes decreasing by 5.5 and 9.5%, respectively, and the c -axis compressing a mere 0.25% up to 1.7 GPa followed by a 0.2% expansion between 1.7 and 4.3 GPa. The 0.2% increase in length of the c -axis in this interval happens above the quasi-hydrostatic limit of the pressure-transmitting medium and therefore it might be a consequence of strain gradients. Under ambient conditions, two MnO 6 units are connected by two carboxylate ligands to form dimeric units. On increasing pressure, a non-bonded O atom from a bridging carboxylate group approaches the Mn atom, with the Mn—O distance decreasing from 2.866 (1) Å at 0.3 GPa to 2.482 (6) Å at 4.3 GPa, increasing the coordination environment of the Mn ion from six- to seven-coordinated.
Publisher: American Chemical Society (ACS)
Date: 03-04-2012
DOI: 10.1021/JA300978F
Abstract: The formation and growth mechanisms in the hydrothermal synthesis of SnO(2) nanoparticles from aqueous solutions of SnCl(4)·5H(2)O have been elucidated by means of in situ X-ray total scattering (PDF) measurements. The analysis of the data reveals that when the tin(IV) chloride precursor is dissolved, chloride ions and water coordinate octahedrally to tin(IV), forming aquachlorotin(IV) complexes of the form [SnCl(x)(H(2)O)(6-x)]((4-x)+) as well as hexaaquatin(IV) complexes [Sn(H(2)O)(6-y)(OH)(y)]((4-y)+). Upon heating, ellipsoidal SnO(2) nanoparticles are formed uniquely from hexaaquatin(IV). The nanoparticle size and morphology (aspect ratio) are dependent on both the reaction temperature and the precursor concentration, and particles as small as ~2 nm can be synthesized. Analysis of the growth curves shows that Ostwald ripening only takes place above 200 °C, and in general the growth is limited by diffusion of precursor species to the growing particle. The c-parameter in the tetragonal lattice is observed to expand up to 0.5% for particle sizes down to 2-3 nm as compared to the bulk value. SnO(2) nanoparticles below 3-4 nm do not form in the bulk rutile structure, but as an orthorhombic structural modification, which previously has only been reported at pressures above 5 GPa. Thus, adjustment of the synthesis temperature and precursor concentration not only allows control over nanoparticle size and morphology but also the structure.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP06018K
Abstract: We present an environmentally benign aqueous synthesis method to obtain fine tunable layered SnS 2 thin films as well as methods to obtain freestanding nanosheets or transfer to flexible substrates.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6TC05068A
Abstract: Cu 8 GeSe 6 argyrodite-type compound is a new thermoelectric material which exhibits extremely low lattice thermal conductivity and high thermoelectric performance.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CC12626A
Abstract: The excited state crystal structure of the ionic complex (Nd(DMA)(4)(H(2)O)(4)-Fe(CN)(6)·3H(2)O (DMA = dimethylacetamide) has been determined at 15 K upon UV illumination by single crystal X-ray diffraction. Significant structural changes are observed around the Fe site in the excited state. These changes are similar to those observed for a related molecular compound exhibiting photomagnetic properties.
Publisher: American Chemical Society (ACS)
Date: 24-09-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CP07648K
Abstract: For both Mg 2.985 Ag 0.015 Sb 2 bulk and powdered s les, an Sb phase appears above ∼500 K but it stabilizes during subsequent thermal cycling.
Publisher: American Physical Society (APS)
Date: 20-02-2008
Publisher: Springer Science and Business Media LLC
Date: 1999
DOI: 10.1557/PROC-590-51
Abstract: Germanium clathrates have recently received attention as potential highly efficient thermoelectric materials based on the phonon glass electron crystal (PGEC) concept [1-4]. A combined EXAFS and XANES study has been performed in order to investigate the local structure and the degree of charge transfer between the guest atoms and the framework atoms. Analysis of the Sr, Ga, and Ge K-edge XANES spectra of a Sr 8 Ga 16 Ge 30 clathrate reveals that the atoms are close to neutrally charged and that the degree of charge transfer is low in agreement with recent theoretical predictions and charge density distribution measurements [3,5].
Publisher: Springer Science and Business Media LLC
Date: 13-12-2016
DOI: 10.1007/S13399-016-0230-X
Abstract: The current paper investigates the use of natural vegetation and agricultural crops commonly found in Scotland as a source of bioenergy. Such biomass is shown to have a high moisture content upon harvest (∼80%) which renders them suitable for wet conversion technologies such as anaerobic digestion (AD) and hydrothermal liquefaction (HTL). Experimental investigations are carried out on 16 different types of biomass to assess their bio-crude yields via HTL and theoretical methane potential via AD based on compositional analysis. The different types of biomass vary significantly in biomass yield upon harvesting from 1.1 t/ha (dry matter) for bracken to a maximum of 17.5 t/ha for winter rye. These area specific yields are the most influential factor in the final energy yield per area. Area specific energy yields are found to average at 67 GJ/ha for AD and 53 GJ/ha for HTL. The respective conversion efficiencies of HTL and AD for different biomass feedstocks are also shown to be an important factor on the overall energy potential. AD averages a mass to energy conversion of 9.1 GJ/t compared to 7.2 GJ/t for HTL. A combination of AD and HTL is investigated by liquefying digestate from rye, but the results suggest this is not a viable option due to low bio-crude yields. However, analysis of the water phase post HTL allowed the calculation of theoretical methane potential from the HTL process water and suggests that this can yield additional energy. Overall, the work shows that utilisation of natural vegetation is a promising approach for bioenergy production.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0DT00742K
Abstract: Phase pure s les of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ∼-250 μV K(-1) was found at 400 K, but the substantial thermal conductivity (∼10 W mK(-1) at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5DT04532K
Abstract: SnS 2 is observed to have a layer compressibility similar to that of graphite, and a reversible color change with pressure is explained from band structure calculations.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8DT01476K
Abstract: Demonstration of a novel method for synthesis of hopeite with high yield and accurate parameter control.
Publisher: American Chemical Society (ACS)
Date: 15-12-2010
DOI: 10.1021/JP109547W
Abstract: High-resolution X-ray diffraction data, coupled with theoretical calculations, are used to demonstrate the presence of a non-nuclear local maximum in the electron density of a dimeric Mg(I) molecule. This is the first time such a non-nuclear attractor (NNA) has been observed in a stable molecular species. Multipole modeling of the Mg(I) centers requires use of expansion/contraction (κ) coefficients taken from density functional theory (DFT), since accurate scattering factors for Mg(I) are not available. The model developed accurately accounts for the electron density in the Mg-Mg region and is in excellent agreement with directly calculated DFT data. Within the quantum theory of atoms in molecules (QTAIM), this molecule is not bound by a Mg-Mg bond but rather by two Mg-"pseudo-atom" bonds. The NNA is associated with a large region of negative Laplacian in the Mg-Mg internuclear region and arises from the overlap of 3s orbitals in this long, nonpolar "bond". The pseudoatomic basin associated with the NNA contains 0.8 electrons, which are highly delocalized and hence weakly bound. Possible implications of this unusual electronic structure for the chemistry of such molecules, including their use as excellent reducing agents, are discussed.
Publisher: International Union of Crystallography (IUCr)
Date: 23-02-2019
DOI: 10.1107/S2052252519001192
Abstract: Characterization of local order in thin films is challenging with pair distribution function (PDF) analysis because of the minute mass of the scattering material. Here, it is demonstrated that reliable high-energy grazing-incidence total X-ray scattering data can be obtained in situ during thin-film deposition by radio-frequency magnetron sputtering. A benchmark system of Pt was investigated in a novel sputtering chamber mounted on beamline P07-EH2 at the PETRA III synchrotron. Robust and high-quality PDFs can be obtained from films as thin as 3 nm and atomistic modelling of the PDFs with a time resolution of 0.5 s is possible. In this way, it was found that a polycrystalline Pt thin film deposits with random orientation at 8 W and 2 × 10 −2 mbar at room temperature. From the PDF it was found that the coherent-scattering domains grow with time. While the first layers are formed with a small tensile strain this relaxes towards the bulk value with increasing film thickness.
Publisher: Hindawi Limited
Date: 2012
DOI: 10.1155/2012/173865
Abstract: Pure phase anatase TiO 2 nanoparticles with sizes of 5–8 nm and varying crystallinity were synthesized in supercritical isopropanol/water using a continuous flow reactor. Their photodegradation of rhodamine B (RhB) was evaluated under visible light irradiation. The as-prepared TiO 2 nanoparticles show much higher photodegradation efficiencies than commercial Degussa P25 TiO 2 . Moreover, the photodegradation of RhB on the as-prepared TiO 2 follows a different process from that on P25 TiO 2 , quicker N-deethylation and slower cleavage of conjugated chromophore structure. Based on PXRD, TEM, and BET measurements, these two photodegradation properties have been explained by the physicochemical properties of TiO 2 .
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CE02224F
Publisher: Wiley
Date: 18-08-2010
Publisher: International Union of Crystallography (IUCr)
Date: 18-08-2019
Publisher: Elsevier BV
Date: 12-2016
Publisher: Springer Science and Business Media LLC
Date: 2001
Abstract: Multi-temperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba 8 Ga 16 Si 30 are analyzed with the maximum entropy method to obtain direct space nuclear densities. The nuclear densities suggest that the guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures.
Publisher: International Union of Crystallography (IUCr)
Date: 15-03-2006
DOI: 10.1107/S160053680600883X
Abstract: The title compound, [Fe 2 Yb 2 (CN) 12 (C 4 H 9 NO) 5 (H 2 O) 6 ]·2H 2 O, is a tetranuclear complex, where the four metal centres are connected through three cyano bridges, the iron centres making one and two bridges, respectively. Each Fe atom is surrounded by six cyano ligands, forming almost ideal octahedra. The two Yb atoms have different ligand environments both are coordinated by seven ligands, consisting of water molecules, dimethylacetamide (DMA) solvent and cyano groups, but not in the same ratio. Four of the five DMA molecules show various degrees of common structural disorder. The asymmetric unit also includes two solvent water molecules, which take part in hydrogen bonding, forming an extended network of tetramers.
Publisher: International Union of Crystallography (IUCr)
Date: 29-08-2014
DOI: 10.1107/S2052252514018570
Abstract: Synchrotron radiation has many compelling advantages over conventional radiation sources in the measurement of accurate Bragg diffraction data. The variable photon energy and much higher flux may help to minimize critical systematic effects such as absorption, extinction and anomalous scattering. Based on a survey of selected published results from the last decade, the benefits of using synchrotron radiation in the determination of X-ray electron densities are discussed, and possible future directions of this field are examined.
Publisher: Elsevier BV
Date: 03-2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CC04827B
Abstract: The available composition space of the high entropy alloy PtIrPdRhRu, synthesized under solvothermal conditions, has been explored varying precursor ratios.
Publisher: Wiley
Date: 12-05-2010
Abstract: Single-crystal X-ray diffraction measurements have been carried out on [Nd(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (1 dmf=dimethylformamide), [Nd(dmf)(4)(H(2)O)(3)(mu-CN)Co(CN)(5)].H(2)O (2), [La(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (3), [Gd(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (4), and [Y(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (5), at 15(2) K with and without UV illumination of the crystals. Significant changes in unit-cell parameters were observed for all the iron-containing complexes, whereas 2 showed no response to UV illumination. Photoexcited crystal structures have been determined for 1, 3, and 4 based on refinements of two-conformer models, and excited-state occupancies of 78.6(1), 84(6), and 86.6(7)% were reached, respectively. Significant bond-length changes were observed for the Fe-ligand bonds (up to 0.19 A), the cyano bonds (up to 0.09 A), and the lanthanide-ligand bonds (up to 0.10 A). Ab initio theoretical calculations were carried out for the experimental ground-state geometry of 1 to understand the electronic structure changes upon UV illumination. The calculations suggest that UV illumination gives a charge transfer from the cyano groups on the iron atom to the lanthanide ion moiety, {Nd(dmf)(4)(H(2)O)(3)}, with a distance of approximately 6 A from the iron atom. The charge transfer is accompanied by a reorganization of the spin state on the {Fe(CN)(6)} complex, and a change in geometry that produces a metastable charge-transfer state with an increased number of unpaired electrons, thus accounting for the observed photomagnetic effect.
Publisher: International Union of Crystallography (IUCr)
Date: 06-03-2021
DOI: 10.1107/S2052252521001664
Abstract: Synchrotron powder X-ray diffraction (PXRD) is a well established technique for investigating the atomic arrangement of crystalline materials. At modern beamlines, X-ray scattering data can be collected in a total-scattering setting, which additionally opens up the opportunity for direct-space structural analysis through the atomic pair distribution function (PDF). Modelling of PXRD and PDF data is typically carried out separately, but employing a concurrent structural model to both direct- and reciprocal-space data has the possibility to enhance total-scattering data analysis. However, total-scattering measurements applicable to such dual-space analyses are technically demanding. Recently, the technical demands have been fulfilled by a MYTHEN microstrip detector system (OHGI), which meets the stringent requirements for both techniques with respect to Q range, Q resolution and dynamic range. In the present study, we evaluate the quality of total-scattering data obtained with OHGI by separate direct- and reciprocal-space analysis of Si. Excellent agreement between structural parameters in both spaces is found, demonstrating that the total-scattering data from OHGI can be utilized in dual-space structural analysis e.g. for in situ and operando measurements.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0NR01240H
Abstract: The redox properties of five common solvents under solvothermal conditions are demonstrated through synthesis and characterization of 3d metal based materials.
Publisher: International Union of Crystallography (IUCr)
Date: 05-1994
Publisher: Wiley
Date: 03-05-1999
DOI: 10.1002/(SICI)1521-3773(19990503)38:9<1239::AID-ANIE1239>3.0.CO;2-9
Publisher: Elsevier BV
Date: 12-2017
Publisher: Wiley
Date: 06-2016
Abstract: The mixed-valence complex Fe3 O(cyanoacetate)6 (H2 O)3 (1) has been studied by single-crystal X-ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mössbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure-induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mössbauer spectra show that the complex becomes partially valence-trapped after the second phase transition. This sluggish pressure-induced valence-trapping is in contrast to the very abrupt valence-trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure.
Publisher: American Chemical Society (ACS)
Date: 04-09-2012
DOI: 10.1021/EF3008163
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.BIORTECH.2015.05.095
Abstract: This work provides a comprehensive characterization of the gas phase from hydrothermal liquefaction of Dried Distillers Grains with Solubles (DDGS) collected during a 24-h continuous experiment. The gas consisted mainly of CO2, CO, H2, CH4 and C2H6 accounting for 96 v/v% while further analysis by gas chromatography coupled to mass spectrometry (GC-MS) showed additionally 62 compounds of which 54 were tentatively identified. These products included methanethiol, dimethyl sulfide, various olefins and several aromatic compounds. The composition provided clear indication of the steady state of the system. Apart from CO2, olefins were the most abundant compound class and could provide a source of revenue.
Publisher: AIP Publishing
Date: 03-04-2023
DOI: 10.1063/5.0144505
Abstract: Ruthenium arsenide is made p-type by the addition of germanium, and it exhibits a large substitution range without affecting the stability. A series of RuAs2−xGex with x = 0.02, 0.04, 0.08, 0.16, 0.32, and 0.64 shows the saturation limit of Ge to be between 0.16 and 0.32. The electrical contribution to the thermoelectric performance is greatly improved with a power factor of 1.03 mW/(m K2). However, the substitution does not affect the rigidity of the lattice, as the Debye temperature remains around 420 K, which means that the thermal conductivity remains high resulting in a modest maximum zT of 0.11.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CP06518H
Abstract: The stoichiometry of g-C 3 N 4 tailored by electron beam irradiation. The data show degradation of g-C 3 N 4 with preferential removal of N species over C species and that inelastic scattering events dominate over elastic events.
Publisher: American Chemical Society (ACS)
Date: 05-09-2007
DOI: 10.1021/CM071435P
Publisher: American Physical Society (APS)
Date: 23-12-2013
Publisher: American Chemical Society (ACS)
Date: 29-08-2014
DOI: 10.1021/CM502042E
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: International Union of Crystallography (IUCr)
Date: 29-06-2022
DOI: 10.1107/S2052252522006315
Abstract: The scattering pattern of a crystal obeys the symmetry of the crystal structure through the corresponding Laue group. This is usually also true for the diffuse scattering, containing information about disorder, but here a case is reported where the diffuse scattering is of lower symmetry than the parent crystal structure. The mineral bixbyite has been studied by X-ray and neutron scattering techniques since 1928 with some of the most recent studies characterizing the low-temperature transition to a magnetically disordered spin-glass state. However, bixbyite also exhibits structural disorder, and here single-crystal X-ray and neutron scattering is used to characterize the different modes of disorder present. One-dimensional rods of diffuse scattering are observed in the cubic mineral bixbyite, which break the expected symmetry of the scattering pattern. It is shown that this scattering arises from epitaxial intergrowths of the related mineral, braunite. The presence of this disorder mode is found to be directly observable as well-defined residuals in the average structure refined against the Bragg diffraction. An additional three-dimensional diffuse scattering component is observed in neutron scattering data, which is shown to originate from the substitutional disorder on the Fe/Mn sites. This occupational disorder gives rise to local relaxations of the oxide sublattice, and the pattern of oxide displacements can be rationalized based on crystal-field theory. The combined use of neutron and X-ray single-crystal scattering techniques highlights their great complementarity. In particular, the large s le requirements for neutron scattering experiments prove to be an obstacle in solving the intergrowth disorder due to several growth orientations, whereas for X-ray scattering the one-dimensional nature of the intergrowth disorder renders solving this a more tractable task. On the other hand, the oxide relaxations cannot be resolved using X-rays due to the low Mn/Fe contrast. By combining the two approaches both types of disorder have been characterized.
Publisher: Springer Science and Business Media LLC
Date: 17-01-2017
DOI: 10.1038/NCOMMS14074
Abstract: The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe 1− x Se x ( x =0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to T c ∼6 K for one unit cell FeTe grown on Bi 2 Te 3 , in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.
Publisher: American Physical Society (APS)
Date: 22-06-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TA01313F
Abstract: We demonstrate that the quality factor of Cu 2 Se 1−x Te x solid solutions is higher than those of most typical thermoelectric materials.
Publisher: International Union of Crystallography (IUCr)
Date: 23-04-2020
DOI: 10.1107/S1600576720003775
Abstract: Hybrid photon-counting detectors are widely established at third-generation synchrotron facilities and the specifications of the Pilatus3 X CdTe were quickly recognized as highly promising in charge-density investigations. This is mainly attributable to the detection efficiency in the high-energy X-ray regime, in combination with a dynamic range and noise level that should overcome the perpetual problem of detecting strong and weak data simultaneously. These benefits, however, come at the expense of a persistent problem for high diffracted beam flux, which is particularly problematic in single-crystal diffraction of materials with strong scattering power and sharp diffraction peaks. Here, an in-depth examination of data collected on an inorganic material, FeSb 2 , and an organic semiconductor, rubrene, revealed systematic differences in strong intensities for different incoming beam fluxes, and the implemented detector intensity corrections were found to be inadequate. Only significant beam attenuation for the collection of strong reflections was able to circumvent this systematic error. All data were collected on a bending-magnet beamline at a third-generation synchrotron radiation facility, so undulator and wiggler beamlines and fourth-generation synchrotrons will be even more prone to this error. On the other hand, the low background now allows for an accurate measurement of very weak intensities, and it is shown that it is possible to extract structure factors of exceptional quality using standard crystallographic software for data processing ( SAINT-Plus , SADABS and SORTAV ), although special attention has to be paid to the estimation of the background. This study resulted in electron-density models of substantially higher accuracy and precision compared with a previous investigation, thus for the first time fulfilling the promise of photon-counting detectors for very accurate structure factor measurements.
Publisher: American Chemical Society (ACS)
Date: 15-01-2020
Publisher: Elsevier BV
Date: 02-2014
Publisher: American Chemical Society (ACS)
Date: 14-02-2019
DOI: 10.1021/JACS.8B12927
Abstract: High-resolution synchrotron and neutron single-crystal diffraction data of 18-crown-6/(pentakis)urea measured at 30 K are combined, with the aim of better appreciating the electrostatics associated with intermolecular interactions in condensed matter. With two 18-crown-6 molecules and five different urea molecules in the crystal, this represents the most ambitious combined X-ray/synchrotron and neutron experimental charge density analysis to date on a cocrystal or host-guest system incorporating such a large number of unique molecules. The dipole moments of the five urea guest molecules in the crystal are enhanced considerably compared to values determined for isolated molecules, and 2D maps of the electrostatic potential and electric field show clearly how the urea molecules are oriented with dipole moments aligned along the electric field exerted by their molecular neighbors. Experimental electric fields in the range of 10-19 GV m
Publisher: IOP Publishing
Date: 2022
DOI: 10.1088/1742-6596/2167/1/012023
Abstract: Advanced radiotherapy techniques, which plan and deliver a treatment in complicated 3D geometries with steep dose gradients, push 3D dosimetry with correspondingly high spatial resolution to the top of scientific and clinical agendas. This paper presents the first steps taken towards an inexpensive and reusable material for 3D dosimetry based on optically stimulated luminescence (OSL). Carbon-doped alumina (Al 2 O 3 :C) nanoparticles were synthesized using supercritical flow synthesis, in which product properties can be finely controlled. The particles were characterized using electron microscopy and powder x-ray diffraction. C-doping did not alter the crystallographic structure appreciably, and a high elemental signal from C could be measured. Nanoparticles of amorphous γ-Al 2 O 3 :C were achieved, however calcining these to produce the OSL-relevant α-phase yielded microparticles. Future work will aim at producing phase-pure α-Al 2 O 3 :C nanoparticles with a narrow size distribution below 10 nm, and controllable C-concentration and O-deficiency.
Publisher: American Chemical Society (ACS)
Date: 20-09-2021
Publisher: Wiley
Date: 05-03-2012
Abstract: Zinc antimonide thin films with high thermoelectric performance are produced by a simple sputtering method. The phase-pure Zn(4)Sb(3) and ZnSb thin films fulfill the key requirements for commercial TE power generation: cheap elements, cheap fabrication method, high performance and thermal stability. In addition, two completely new meta-stable crystalline phases of zinc antimonide have been discovered.
Publisher: American Chemical Society (ACS)
Date: 05-11-2012
DOI: 10.1021/CG301230W
Publisher: Wiley
Date: 28-09-2023
Publisher: Wiley
Date: 04-08-2000
DOI: 10.1002/1521-3773(20000804)39:15<2719::AID-ANIE2719>3.0.CO;2-8
Publisher: Wiley
Date: 03-10-2014
Publisher: American Physical Society (APS)
Date: 02-03-2006
Publisher: American Chemical Society (ACS)
Date: 24-05-2013
DOI: 10.1021/CM4008393
Publisher: Wiley
Date: 22-09-2003
Abstract: Periodic density functional calculations using pseudopotentials and a local basis set were performed on the type I clathrates A(8)Ga(16)Ge(30) (A=Sr, Ba). Both are known to show promising thermoelectric properties. Ab initio wave functions were analyzed within the framework of the quantum theory of atoms in molecules. This enabled us to analyze both the charge transfer and bonding properties of the clathrate from a rigorous quantum mechanical viewpoint. The Ba and Sr centers were found to be largely ionic (charge: ca. +1.7 e) both in the smaller 20-atom and in the larger 24-atom cages, consistent with a Zintl-phase view of these type I clathrates. The assertion that the Sr atoms in the different cages have similar oxidation states is shown to be consistent with multiwavelength diffraction experiments on Sr(8)Ga(16)Ge(30) while the assertion of ionicity of the Sr center is supported by the observation that the adsorption edge lies close to that previously found in the Sr K-edge XANES spectra of Sr(OH)(2).8 H(2)O. As such, this work contradicts previous experimental and theoretical studies that claim that the guest atoms are neutral. We show that the discrepancy is related to the definitions used for electron transfer. Definitions based on electron displacement (rearrangement) in space, as in previous works, do not account for the variation in shape and volume of the atomic catchment regions upon change in the number and average locations of the particles in the system. Eventually, such definitions lead to underestimation of charge transfer. The large binding energy found in earlier work for Ba and Sr in these materials is found to be consistent with a simple picture of charge transfer from the guest to the frame. Preliminary investigations on a clathrate of perfect stoichiometry appear to rule out any important relationship between the observed increase in the thermoelectric figure of merit with increasing external pressure and host-guest charge transfer.
Publisher: AIP Publishing
Date: 21-03-2003
DOI: 10.1063/1.1556591
Publisher: American Chemical Society (ACS)
Date: 26-07-2012
DOI: 10.1021/IC301372M
Abstract: One of the most basic concepts in chemical bonding theory is the octet rule, which was introduced by Lewis in 1916, but later challenged by Pauling to explain the bonding of third-row elements. In the third row, the central atom was assumed to exceed the octet by employing d orbitals in double bonding leading to hypervalency. Ever since, polyoxoanions such as SO(4)(2-), PO(4)(3-), and ClO(4)(-) have been paradigmatic ex les for the concept of hypervalency in which the double bonds resonate among the oxygen atoms. Here, we examine S-O bonding by investigating the charge density of the sulfate group, SO(4)(2-), within a crystalline environment based both on experimental and theoretical methods. K(2)SO(4) is a high symmetry inorganic solid, where the crystals are strongly affected by extinction effects. Therefore, high quality, very low temperature single crystal X-ray diffraction data were collected using a small crystal (∼30 μm) and a high-energy (30 keV) synchrotron beam. The experimental charge density was determined by multipole modeling, whereas a theoretical density was obtained from periodic ab initio DFT calculations. The chemical bonding was jointly analyzed within the framework of the Quantum Theory of Atoms In Molecules only using quantities derived from an experimental observable (the charge density). The combined evidence suggests a bonding situation where the S-O interactions can be characterized as highly polarized, covalent bonds, with the "single bond" description significantly prevailing over the "double bond" picture. Thus, the study rules out the hypervalent description of the sulfur atom in the sulfate group.
Publisher: Wiley
Date: 15-08-2012
Abstract: Supercritical growth: The formation and evolution of ceria nanoparticles during hydrothermal synthesis was investigated by in situ total scattering and powder diffraction. The nucleation of pristine crystalline ceria nanoparticles originated from previously unknown cerium dimer complexes. The nanoparticle growth was highly accelerated under supercritical conditions.
Publisher: Springer Science and Business Media LLC
Date: 09-11-2018
DOI: 10.1038/S41467-018-06980-X
Abstract: The Mg 3 Sb 2 structure is currently being intensely scrutinized due to its outstanding thermoelectric properties. Usually, it is described as a layered Zintl phase with a clear distinction between covalent [Mg 2 Sb 2 ] 2− layers and ionic Mg 2+ layers. Based on the quantitative chemical bonding analysis, we unravel instead that Mg 3 Sb 2 exhibits a nearly isotropic three-dimensional bonding network with the interlayer and intralayer bonds being mostly ionic and surprisingly similar, which results in the nearly isotropic structural and thermal properties. The isotropic three-dimensional bonding network is found to be broadly applicable to many Mg-containing compounds with the CaAl 2 Si 2 -type structure. Intriguingly, a parameter based on the electron density can be used as an indicator measuring the anisotropy of lattice thermal conductivity in Mg 3 Sb 2 -related structures. This work extends our understanding of structure and properties based on chemical bonding analysis, and it will guide the search for and design of materials with tailored anisotropic properties.
Publisher: American Chemical Society (ACS)
Date: 29-01-2013
DOI: 10.1021/JP308777N
Publisher: AIP Publishing
Date: 04-03-2008
DOI: 10.1063/1.2885067
Abstract: We review the phonon analysis of FeSi and present a new study of the Raman and infrared (IR) active phonons of the related compound FeSb2. The measurements are supplemented by a factor group analysis, enabling the full mode assignment. While in FeSi, all nine Raman active modes predicted by the theory are visible in our spectra, in FeSb2, three of the six predicted modes have been observed. The unusual temperature dependence of the Raman linewidth of FeSi has been interpreted in terms of electron-phonon interactions. In FeSb2, a Fano-like IR absorption is reported at 300K, indicating electron-phonon coupling. The asymmetry vanishes and the d ing constant decreases drastically by cooling, in correspondence with the depletion of the charge carrier concentration.
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: American Physical Society (APS)
Date: 24-05-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2SC04522B
Abstract: Zr 4+ solution structures have been determined using X-ray pair distribution function analysis across pH, concentrations, solvents and metal sources.
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A701978E
Publisher: American Chemical Society (ACS)
Date: 28-07-2011
DOI: 10.1021/CM201330X
Publisher: Wiley
Date: 09-10-2019
Publisher: IOP Publishing
Date: 17-09-2007
Publisher: American Chemical Society (ACS)
Date: 03-09-2014
DOI: 10.1021/EF5012808
Publisher: AIP Publishing
Date: 14-02-2011
DOI: 10.1063/1.3556645
Abstract: Substitution of Sb in FeSb2 by less than 0.5% of Te induces a transition from a correlated semiconductor to an unconventional metal with large effective charge carrier mass m∗. Spanning the entire range of the semiconductor-metal crossover, we observed an almost constant enhancement of the measured thermopower compared to that estimated by the classical theory of electron diffusion. Using the latter for a quantitative description one has to employ an enhancement factor of 10–30. Our observations point to the importance of electron-electron correlations in the thermal transport of FeSb2, and suggest a route to design thermoelectric materials for cryogenic applications.
Publisher: American Chemical Society (ACS)
Date: 19-01-2011
DOI: 10.1021/IC102008A
Abstract: Ni(HCOO)(2)(H(2)O)(2) is a structurally simple coordination polymer showing interesting magnetic phase transitions at low temperature (<16K). Previously published studies of these phase transitions have yielded inconsistent results, questioning the correctness of the published magnetic structure. Here heat capacity and magnetic susceptibility of a fully, a partly and a non-deuterated s le were measured, and they all exhibit magnetic phase transitions around 3 and 15 K. Neutron powder diffraction data was collected on the fully deuterated s le at various temperatures between 1.5 and 25 K. A magnetic model was refined against the neutron diffraction data using a spin system composed of two canted antiferromagnetic sublattices. The magnetic moments of the two sublattices show different magnitude, 1.7 μ(B) and 1.3 μ(B), and the temperature dependence of the magnetic sublattices is quite different. One of the sublattices shows the expected temperature behavior of an antiferromagnetic compound whereas the other sublattice follows a Brillouin like function with a slowly increasing magnetization below the Néel temperature.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NR01228A
Abstract: Li-Intercalation in nano-rutile TiO 2 -anodes induces loss of long-range order with the formation of ∼5 nm layered Li x TiO 2 domains with ∼1 nm columbite-like grain boundaries.
Publisher: JMIR Publications Inc.
Date: 14-10-2022
Abstract: ournal articles describing randomized controlled trials (RCTs) and systematic reviews with meta-analysis of RCTs are not optimally reported and often miss crucial details. This poor reporting makes assessing these studies’ risk of bias or reproducing their results difficult. However, the reporting quality of diet- and nutrition-related RCTs and meta-analyses has not been explored. e aimed to assess the reporting completeness and identify the main reporting limitations of diet- and nutrition-related RCTs and meta-analyses of RCTs, estimate the frequency of reproducible research practices among these RCTs, and estimate the frequency of distorted presentation or spin among these meta-analyses. wo independent meta-research studies will be conducted using articles published in PubMed-indexed journals. The first will include a s le of diet- and nutrition-related RCTs the second will include a s le of systematic reviews with meta-analysis of diet- and nutrition-related RCTs. A validated search strategy will be used to identify RCTs of nutritional interventions and an adapted strategy to identify meta-analyses in PubMed. We will search for RCTs and meta-analyses indexed in 1 calendar year and randomly select 100 RCTs (June 2021 to June 2022) and 100 meta-analyses (July 2021 to July 2022). Two reviewers will independently screen the titles and abstracts of records yielded by the searches, then read the full texts to confirm their eligibility. The general features of these published RCTs and meta-analyses will be extracted into a research electronic data capture database (REDCap Vanderbilt University). The completeness of reporting of each RCT will be assessed using the items in the CONSORT (Consolidated Standards of Reporting Trials), its extensions, and the TIDieR (Template for Intervention Description and Replication) statements. Information about practices that promote research transparency and reproducibility, such as the publication of protocols and statistical analysis plans will be collected. There will be an assessment of the completeness of reporting of each meta-analysis using the items in the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) statement and collection of information about spin in the abstracts and full-texts. The results will be presented as descriptive statistics in diagrams or tables. These 2 meta-research studies are registered in the Open Science Framework. he literature search for the first meta-research retrieved 20,030 records and 2182 were potentially eligible. The literature search for the second meta-research retrieved 10,918 records and 850 were potentially eligible. Among them, random s les of 100 RCTs and 100 meta-analyses were selected for data extraction. Data extraction is currently in progress, and completion is expected by the beginning of 2023. ur meta-research studies will summarize the main limitation on reporting completeness of nutrition- or diet-related RCTs and meta-analyses and provide comprehensive information regarding the particularities in the reporting of intervention studies in the nutrition field. ERR1-10.2196/43537
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2NR07128B
Abstract: Gallium oxides are of broad interest due to their wide band gaps and attractive photoelectric properties. Exploration of their formation mechanisms lead to phase control during synthesis.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0MA00949K
Abstract: The performance of aqueous CuHCF/Zn batteries are highly dependent on the CuHCF s le. With Na-based electrolyte the capacity retention improves at low pH, whereas cells with Zn-based electrolyte have similar performance at pH 2 and pH 4.
Publisher: Elsevier BV
Date: 12-2017
Publisher: Wiley
Date: 24-07-2017
Publisher: International Union of Crystallography (IUCr)
Date: 15-11-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP50365H
Abstract: 20 nm ZnO nanoparticles are used to fabricate the mesoporous photoanode of the CdS/CdSe quantum dot-sensitized solar cells by the simple doctor blade method. A maximum power conversion efficiency of 4.46% has been achieved, which indicated exciting prospects for ZnO nanoparticle based quantum dot-sensitized solar cells.
Publisher: American Chemical Society (ACS)
Date: 25-03-2019
Publisher: Springer Science and Business Media LLC
Date: 30-07-2012
DOI: 10.1557/JMR.2012.234
Publisher: American Chemical Society (ACS)
Date: 19-05-2015
Publisher: Wiley
Date: 18-09-2019
Abstract: Rational material design requires a deep understanding about the relationship between the structure and properties of materials, which are both intimately related to their chemical bonding. Through the experimentally observable electron density, chemical bonding can be understood from experimental and theoretical points of view on an equal footing, and advances in accurate X-ray diffraction measurements and computational techniques over the past decades have provided access to electron density distributions in increasingly complex functional materials. In this Review, selected electron density studies from the literature on a wide range of materials classes are presented, including studies of thermoelectric materials, high pressure electrides, coordination polymers and non-linear optical materials. These studies demonstrate how detailed analysis of chemical bonding based on the electron density provides important understanding of materials beyond arguments based on structure and simple chemical concepts. In cases such as understanding the conducting properties of Zintl semiconductors or the effect of mutual electrical polarization in host-guest systems, it is clearly imperative to go beyond structure and examine the chemical bonding in detail. In the Review, the complementarity between theory and experiment is underlined, which allows for mutual validation of new chemical bonding concepts, and indeed experiment and theory may challenge each other based on the different strengths and weaknesses of each method.
Publisher: The Electrochemical Society
Date: 2011
DOI: 10.1149/2.084202JES
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9NR09069J
Abstract: Rutile TiO 2 nanocrystals are synthesized for the first time in a continuous flow hydrothermal process.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0NR08587A
Abstract: The indium oxides, c-In 2 O 3 , h-In 2 O 3 , InOOH and In(OH) 3 , have been studied by in situ X-ray scattering to determine the formation and transformation mechanisms in this system of important wide band gap semiconductors.
Publisher: International Union of Crystallography (IUCr)
Date: 06-1999
DOI: 10.1107/S0108768198010398
Abstract: Extensive synchrotron (28 K) and conventional sealed-tube (9 K) X-ray diffraction data have been collected on tetrakis(dimethylphosphinodithioato- S , S ′)thorium(IV), [Th(S 2 PMe 2 ) 4 ]. The use of very low temperatures, well below those obtained with liquid-nitrogen cooling, is crucial for the accuracy of the data. This is due to minimization of temperature-dependent systematic errors such as TDS and anharmonicity, and extension and intensification of the data in reciprocal space. Comparison of structural parameters derived separately from the sealed-tube data and the synchrotron data shows good agreement. The synchrotron data are markedly superior when comparing refinement residuals, standard uncertainties (s.u.'s) of the data and s.u.'s of the derived parameters. However, the study suggests that there are still small uncorrected systematic errors in the data. The very large extent [(\\sin\\theta/\\lambda) max = 1.77 Å −1 ] of the synchrotron data and the very low temperature at which they were collected makes it possible to separate anharmonic effects from electron-deformation effects even with only an X-ray data set at a single temperature. The electron density shows a large polarization of the outer Th core of d -type symmetry. This deformation is successfully modelled with contracted multipolar functions, which are only slightly correlated with anharmonic expansions in reciprocal space when using the full extent of the data. In the data collection more than a factor of 100 in speed is gained by use of image-plate area detectors at the synchrotron source compared with conventional sequential measurements. Thus accurate, very low temperature synchrotron-radiation diffraction data can now be measured within days, which makes electron-density studies of compounds beyond the first transition series more frequently within reach.
Publisher: Elsevier BV
Date: 05-2021
Publisher: AIP Publishing
Date: 28-01-2005
DOI: 10.1063/1.1852072
Abstract: The properties of Te-doped Co(Sb1−yTey)3 and Te-Ni double-doped Co1−xNix(Sb1−yTey)3 nanostructured skutterudites were evaluated by means of x-ray powder diffraction, and transport properties measured on the synthesized s les have been compared with ab initio theoretical modeling. Theoretical optimal dopant contents have been evaluated according to the maximum value of the power factor, calculating the electronic transport properties from the ab initio material band structure using semiclassical Boltzmann transport theory. The s les have been synthesized by chemical alloying with Te substitution for Sb up to 2.5at.% and Ni substitution for Co up to 2.0at.%. X-ray powder diffraction has been performed on all s les to reveal information about phase purity and Rietveld refinement was performed for the phase composition and cell parameter. The thermoelectric properties of the resulting consolidates were investigated in a temperature range from 300to723K using various measurement facilities. A standardization and round robin program was started among the participating evaluation laboratories in order to ensure reliability of the data obtained. The significant reduction in thermal conductivity, when compared to highly annealed CoSb3, could be proved which is caused by the nanostructuring, resulting in a high concentration of grain boundaries. A combination of substitution levels for Ni and Te has been found resulting in the largest ZT value of 0.65 at 680K among unfilled skutterudite materials.
Publisher: Elsevier BV
Date: 07-2012
Publisher: International Union of Crystallography (IUCr)
Date: 26-06-2019
DOI: 10.1107/S205327331900799X
Abstract: Electron density determination based on structure factors obtained through powder X-ray diffraction has so far been limited to high-symmetry inorganic solids. This limit is challenged by determining high-quality structure factors for crystalline urea using a bespoke vacuum diffractometer with imaging plates. This allows the collection of data of sufficient quality to model the electron density of a molecular system using the multipole method. The structure factors, refined parameters as well as chemical bonding features are compared with results from the high-quality synchrotron single-crystal study by Birkedal et al. [ Acta Cryst. (2004), A 60 , 371–381] demonstrating that powder X-ray diffraction potentially provides a viable alternative for electron density determination in simple molecular crystals where high-quality single crystals are not available.
Publisher: International Union of Crystallography (IUCr)
Date: 17-02-2023
DOI: 10.1107/S2052252523001318
Abstract: The superionic conductor Cu 2− x Se has regained interest as a thermoelectric material owing to its low thermal conductivity, suggested to arise from a liquid-like Cu substructure, and the material has been coined a phonon-liquid electron-crystal. Using high-quality three-dimensional X-ray scattering data measured up to large scattering vectors, accurate analysis of both the average crystal structure as well as the local correlations is carried out to shed light on the Cu movements. The Cu ions show large vibrations with extreme anharmonicity and mainly move within a tetrahedron-shaped volume in the structure. From the analysis of weak features in the observed electron density, the possible diffusion pathway of Cu is identified, and it is clear from its low density that jumps between sites are infrequent compared with the time the Cu ions spend vibrating around each site. These findings support the conclusions drawn from recent quasi-elastic neutron scattering data, casting doubt on the phonon-liquid picture. Although there is diffusion of Cu ions in the structure, making it a superionic conductor, the jumps are infrequent and probably not the origin of the low thermal conductivity. From three-dimensional difference pair distribution function analysis of the diffuse scattering data, strongly correlated movements are identified, showing atomic motions which conserve interatomic distances at the cost of large changes in angles.
Publisher: AIP Publishing
Date: 10-05-2016
DOI: 10.1063/1.4948334
Abstract: The origin of the “glass-like” plateau in thermal conductivity of inorganic type I clathrates has been debated for more than a decade. Here, it is demonstrated that the low temperature thermal conductivity of Sr8Ga16Ge30 can be controlled by the synthesis method: A flux-grown s le has a “glass-like” plateau in thermal conductivity at low temperature, while a zone-melted s le instead has a crystalline peak. A combination of flux-growth and zone-melting produces an intermediate thermal conductivity. In a comprehensive study of three single crystal s les, it is shown by neutron diffraction that the transition from crystalline peak to “glass-like” plateau is related to an increase in Sr guest atom off-centering distance from 0.24 Å to 0.43 Å. By modifying ab initio calculated force constants for the guest atom to an isotropic model, we reproduce both measured heat capacity and inelastic neutron scattering data. The transition from peak to plateau in the thermal conductivity can be modeled by a combined increase of Rayleigh and disorder scattering. Measurement of heat capacity refutes simple models for tunneling of Sr between off-center sites. Furthermore, the electronic properties of the same s les are characterized by Hall carrier density, Seebeck coefficient, and resistivity. The present comprehensive analysis excludes tunneling and charge carrier scattering as dominant contributors to the “glass-like” plateau. The increased guest atom off-centering distance controlled by synthesis provides a possible microscopic mechanism for reducing the low temperature thermal conductivity of clathrates.
Publisher: International Union of Crystallography (IUCr)
Date: 18-10-2012
Publisher: AIP
Date: 2012
DOI: 10.1063/1.4731565
Publisher: American Chemical Society (ACS)
Date: 20-05-2020
Publisher: Proceedings of the National Academy of Sciences
Date: 29-10-2021
Abstract: With rare exceptions, an antiferromagnetic (AFM) transition in zero magnetic field is thermodynamically of second order where the thermal-average magnetic moments of the magnetic atoms (ordered moments) vary continuously on cooling through the AFM ordering temperature T N with no latent heat at the transition. Such materials include the AFM pnictides CaMn 2 As 2 , SrMn 2 As 2 , CaMn 2 Sb 2 , SrMn 2 Sb 2 , and CaMn 2 Bi 2 . Here we demonstrate that the closely related SrMn 2 P 2 and CaMn 2 P 2 insulators instead exhibit first-order AFM transitions at T N = 53 and 70 K, respectively, where the heat capacity exhibits a latent heat at T N . The mechanism causing these first-order transitions remains to be explained, but its understanding may lead to the development of novel magnetic materials of technological interest.
Publisher: American Chemical Society (ACS)
Date: 03-10-2019
DOI: 10.1021/JACS.9B07659
Abstract: The direct growth of Pt islands on lattice mismatched Ni nanoparticles is a major synthetic challenge and a promising strategy to create highly strained Pt atoms for electrocatalysis. By using very mild reaction conditions, Pt islands with tunable strain were formed directly on Ni branched particles. The highly strained 1.9 nm Pt-island on branched Ni nanoparticles exhibited high specific activity and the highest mass activity for hydrogen evolution (HER) in a pH 13 electrolyte. These results show the ability to synthetically tune the size of the Pt islands to control the strain to give higher HER activity.
Publisher: International Union of Crystallography (IUCr)
Date: 25-08-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0DT02795B
Abstract: A range of experimental techniques is used to quantify how disorder varies with synthesis conditions in spinel ZnAl 2 O 4 .
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2DT30278K
Abstract: High resolution single crystal synchrotron X-ray diffraction data measured at 15(2) K were used to solve the structure of the complex intermetallic Zintl phase, Yb(11)AlSb(9) (space group Iba2), made up of Yb cations and polyanions along with isolated Sb anions. The 15(2) K cell parameters are a = 11.7383(4) Å, b = 12.3600(4) Å, c = 16.6796(6) Å. The temperature dependence of the structure was investigated through high resolution synchrotron powder X-ray diffraction (PXRD) data measured from 90 K to 1000 K. Rietveld refinements of the crystal structure revealed near linear thermal expansion of Yb(11)AlSb(9) with expansion coefficients of 1.49(2) × 10(-5) K(-1), 1.71(3) × 10(-5) K(-1), 1.13(1) × 10(-5) K(-1) for a, b and c, respectively. The chemical bonding in Yb(11)AlSb(9) was analyzed using atomic Hirshfeld surfaces, and the analysis supports the presence of the structural elements of Yb cations, [AlSb(4)](9-) tetrahedra, [Sb(2)](4-) dimers and isolated Sb(3-) anions. However, indications of interatomic interactions between the Zintl anions and the Yb cations were also observed.
Publisher: American Chemical Society (ACS)
Date: 12-12-2013
DOI: 10.1021/JP4106713
Publisher: Wiley
Date: 29-05-2017
Publisher: Wiley
Date: 16-02-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA41854E
Publisher: Springer Science and Business Media LLC
Date: 22-02-2013
Publisher: Wiley
Date: 24-06-2019
Publisher: American Chemical Society (ACS)
Date: 02-03-2015
DOI: 10.1021/AM508432W
Abstract: The global ambition of reducing the carbon dioxide emission makes sequestration reactions attractive as an option of storing CO2. One promising environmentally benign technology is based on forming thermodynamically stable carbonated minerals, with the drawback that these reactions usually have low conversion rates. In this work, the carbonation reaction of Mg rich olivine, Mg2SiO4, under supercritical conditions has been studied. The reaction produces MgCO3 at elevated temperature and pressure, with the addition of NaHCO3 and NaCl to improve the reaction rates. A sequestration rate of 70% was achieved within 2 h, using olivine particles of sub-10 μm, whereas 100% conversion was achieved in 4 h. This is one of the fastest complete conversions for this reaction reported to date. The CO2 sequestration rate is found to be highly dependent on the applied temperature and pressure, as well as the addition of NaHCO3. In contrast, adding NaCl was found to have limited effect on the reaction rate. The roles of NaHCO3 and NaCl as catalysts are discussed and especially how their effect changes with increased olivine particle size. The products have been characterized by Rietveld refinement of powder X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy revealing the formation of amorphous silica and micrometer-sized magnesium carbonate crystals.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7SE00090A
Abstract: Hydrocarbon fuel (alkanes and aromatics) production via catalytic hydrotreatment of bio-crude from pilot scale HTL.
Publisher: IEEE
Date: 06-2007
Publisher: International Union of Crystallography (IUCr)
Date: 22-02-2022
DOI: 10.1107/S205252062101310X
Abstract: Thermoelectric materials allow for conversion of waste heat into electrical energy, and they represent a green solution for improving our energy efficiency. Inclusion of 4 f electrons near the Fermi level may boost the Seebeck coefficient, which is essential for high thermoelectric performance. In this study, Ce was successfully substituted for Ba on the guest atom sites in the type-I clathrate Ba 8– x Ce x Au y Si 46– y and the material was characterized using high-resolution synchrotron powder X-ray diffraction data measured from 100 K to 1000 K to investigate potential structural implications of the inclusion of a 4 f element. The thermal expansion and bonding of the host structure are not affected by the presence of Ce, as seen from the linear coefficient of unit-cell thermal expansion of 7.30 (8) × 10 −6 K −1 and the average host Debye temperature of 404 (7) K determined from the multi-temperature atomic displacement parameters, both of which are similar to values obtained for pure Ba 8 Au y Si 46– y . The anisotropic atomic displacement parameters on the guest atom site in the large clathrate cage populated by Ba surprisingly reveals isotropic behavior, which is different from all other clathrates reported in literature, and thus represents a unique host–guest bonding situation.
Publisher: International Union of Crystallography (IUCr)
Date: 14-08-2015
DOI: 10.1107/S2052252515012130
Abstract: Rubrene is one of the most studied organic semiconductors to date due to its high charge carrier mobility which makes it a potentially applicable compound in modern electronic devices. Previous electronic device characterizations and first principles theoretical calculations assigned the semiconducting properties of rubrene to the presence of a large overlap of the extended π-conjugated core between molecules. We present here the electron density distribution in rubrene at 20 K and at 100 K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically, the presence of C π ...C π interactions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI) analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by H—H interactions. The electron density features of H—H bonding, and the interaction energy of molecular dimers connected by H—H interaction clearly demonstrate an importance of these weak interactions in the stabilization of the crystal structure. The quantitative nature of the intermolecular interactions is virtually unchanged between 20 K and 100 K suggesting that any changes in carrier transport at these low temperatures would have a different origin. The obtained experimental results are further supported by theoretical calculations.
Publisher: Wiley
Date: 21-06-2011
Publisher: International Union of Crystallography (IUCr)
Date: 12-1996
DOI: 10.1107/S010876819600794X
Abstract: Structural parameters derived from 9 1) K X-ray diffraction data and 13 (1) K time-of-flight neutron diffraction data on perdeuterated tetraamminedinitronickel(II), Ni(ND 3 ) 4 (NO 2 ) 2 , are compared. It is shown that excellent agreement can be obtained for both positional and thermal parameters derived separately from the two experiments, provided that great care is taken in all steps of the process, including data collection, data reduction, and nuclear and electronic structure refinement. The mean difference in the thermal parameters, | ΔU ij | , is as low as 0.00034 Å 2 and ( ΔU ij /σ ) 2 1/2 = 1.92, showing that, even without any form of scaling between the parameters, the same values can be obtained. This, compared with other such studies, indicates that time-of-flight neutron diffraction data can give structural information of a quality comparable to monochromatic neutron diffraction. The excellent correspondence between the thermal parameters derived separately from X-ray and neutron diffraction data gives confidence in the deconvolution of the thermal motion from the X-ray diffraction data, which is necessary for any study of a static electron density distribution.
Publisher: American Chemical Society (ACS)
Date: 19-09-2001
DOI: 10.1021/JP011328X
Publisher: International Union of Crystallography (IUCr)
Date: 28-03-2018
DOI: 10.1107/S1600576718003552
Abstract: In situ powder X-ray diffraction (PXRD) is a powerful characterization tool owing to its ability to provide time-resolved information about phase composition, crystal structure and microstructure. The application of high-flux synchrotron X-ray beams and the development of custom-built reactors have facilitated second-scale time-resolved studies of nanocrystallite formation and growth during solvothermal synthesis. The short exposure times required for good time resolution limit the data quality, while the employed high-temperature–high-pressure reactors further complicate data acquisition and treatment. Based on experience gathered during ten years of conducting in situ studies of solvothermal reactions at a number of different synchrotrons, a compilation of useful advice for conducting in situ PXRD experiments and data treatment is presented here. In addition, the reproducibility of the employed portable in situ PXRD setup, experimental procedure and data analysis is evaluated. This evaluation is based on repeated measurements of an LaB 6 line-profile standard throughout 5 d of beamtime and on the repetition of ten identical in situ synchrotron PXRD experiments on the hydrothermal formation of γ-Fe 2 O 3 nanocrystallites. The study reveals inconsistencies in the absolute structural and microstructural values extracted by Rietveld refinement and whole powder pattern modelling of the in situ PXRD data, but also illustrates the robustness of trends and relative changes in the extracted parameters. From the data, estimates of the effective errors and reproducibility of in situ PXRD studies of solvothermal nanocrystallite formation are provided.
Publisher: American Chemical Society (ACS)
Date: 17-01-2013
DOI: 10.1021/AM302360G
Abstract: A novel, facile, and low-cost method was developed for manufacturing Pt counter electrodes (CEs) of dye-sensitized solar cells (DSCs) on the indium tin oxide-coated polyethylene terephthalate (ITO-PET). This press-transferring method reconciled the temperature conflict between the sintering process of thermal decomposition of H(2)PtCl(6) and plastic substrates. Cyclic voltammograms, electrochemical impedance spectroscopy, transmittance spectra and photovoltaic performance were characterized to investigate the transferred Pt CEs. It was found that the transferred Pt CEs on ITO-PET exhibited an excellent catalytic activity comparable with traditional electrodes on FTO glasses. On the front-side, an illuminated conversion efficiency of 7.21% was reached with more than 94% efficiency of conventional thermally deposited Pt CEs on FTO glasses, and on the back-side, the illuminated conversion efficiency was 4.86%, which was higher than that for conventional electrodes.
Publisher: American Chemical Society (ACS)
Date: 20-01-2012
DOI: 10.1021/IC202231K
Abstract: The Mn atom in the cubic polymorph of CeMnNi(4) appears to be located in an oversized cage-like structure, and anomalously large atomic displacement parameters (ADPs) for the Mn atom indicate that it is a potential "rattler" atom. Here, multitemperature synchrotron powder X-ray diffraction data measured between 110 and 900 K are used to estimate ADPs for the Mn "guest" atom and the "host" structure atoms in cubic CeMnNi(4). The ADPs are subsequently fitted with Debye and Einstein models, giving Θ(D) = 301(2) K for the "host" structure and Θ(E) = 165(2) K for the Mn atom. This is higher than typical Einstein temperatures for rattlers in thermoelectric skutterudites and clathrates (Θ(E) = 50-80 K), indicating that the Mn atom in cubic CeMnNi(4) is more strongly bonded. In order to probe the chemical interactions of the potential Mn rattler atom, atomic Hirshfeld surface (AHS) analysis is carried out and compared with AHS analysis of well-established guest atom rattlers in archetypical skutterudites, MCoSb(3). Surprisingly, the skutterudite rattlers have more deformed AHSs than the Mn atom in cubic CeMnNi(4). This is related to the highly ionic nature of the skutterudite rattlers, which is not taken into account in the neutral spherical atom approach of the AHS. Additionally, visualization of void spaces in the two materials using the procrystal electron density shows that while the Mn atom is tightly fitting in the CeMnNi(4) structure then the La atom in the skutterudite is truly situated in an oversized cage of the host structure. Overall, we conclude that the Mn atom in cubic CeMnNi(4) cannot be coined a rattler.
Publisher: American Chemical Society (ACS)
Date: 03-08-2011
DOI: 10.1021/CG200596C
Publisher: American Chemical Society (ACS)
Date: 15-12-2017
Publisher: American Chemical Society (ACS)
Date: 18-09-2014
DOI: 10.1021/IC501152J
Abstract: Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large ersity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K(+)-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na(+) and K(+) ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating s le magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties.
Publisher: American Chemical Society (ACS)
Date: 06-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8NR03102A
Abstract: A prominent surface acoustic wave dominates the vibrational dynamics of Bi 2 Te 3 (111). Theoretical calculations reveal the crucial role of vdW interactions.
Publisher: American Chemical Society (ACS)
Date: 17-04-2014
DOI: 10.1021/NN5010638
Abstract: The formation, growth, and phase transition of colloidal monodisperse spherical copper sulfide nanocrystals synthesized in dodecanethiol have been followed by in situ synchrotron powder X-ray diffraction (PXRD). The formation of nanocrystals involves a thermal decomposition of the crystalline precursor [CuSC12H25], which upon heating forms an isotropic liquid that subsequently turns into colloidal β-chalcocite phase Cu2S nanocrystals. The redox reaction step in the precursor solution has been studied by proton NMR. Upon heating, high digenite phase nanocrystals are formed through a solid-state rearrangement phase transition of the β-chalcocite phase nanocrystals at temperatures above 260 °C. TEM and PXRD reveal that the nanocrystal size is independent of synthesis temperature and stabilizes after the phase transition has completed. Spherical monodisperse nanocrystals are obtained in all experiments, with the nanocrystals in the β-chalcocite phase (7 nm) being smaller than those in high digenite phase (11 nm).
Publisher: International Union of Crystallography (IUCr)
Date: 10-11-2012
DOI: 10.1107/S0909049512039441
Abstract: In a powder diffraction pattern one measures the intensity of Miller-indexed Bragg peaks versus the wavevector transfer sinθ/λ. With increasing wavevector transfer the density of occurrence of Bragg peaks increases while their intensity decreases until they vanish into the background level. The lowest possible background level is that due to Compton scattering from the powder. A powder diffraction instrument has been designed and tested that yields this ideal low-background level, obtainable by having the space between s le and detector all in vacuum with the entrance window so far upstream that scattering from it is negligible. To minimize overlap of Bragg peaks the combination of fine collimation of synchrotron radiation, a thin cylindrical s le and a high-resolution imaging plate detector is taken advantage of.
Publisher: American Chemical Society (ACS)
Date: 20-02-2018
Publisher: Elsevier BV
Date: 04-2003
Publisher: Wiley
Date: 29-05-2019
Publisher: Wiley
Date: 16-04-2014
Abstract: In this contribution, the solid-state low-temperature phase structure of [2,2]-paracyclophane is unambiguously characterised by single-crystal X-ray analysis. Additionally, a heat capacity measurement was undertaken, which proves the existence of a λ-type phase transition at 45 K, a transition that is connected with the formation of a secondary Cp/T feature at 60 K. The low-temperature phase ( 60 K) crystallises in space group P4(2)/mnm. This proves what has been postulated both by experimental and theoretical chemists but has repeatedly been dismissed as speculation many times.
Publisher: American Chemical Society (ACS)
Date: 23-10-2012
DOI: 10.1021/EF300954E
Publisher: Springer Science and Business Media LLC
Date: 02-08-2021
Publisher: American Chemical Society (ACS)
Date: 20-01-2011
DOI: 10.1021/CM102575W
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.BIORTECH.2016.08.053
Abstract: Hydrothermal liquefaction (HTL) is a promising thermo-chemical processing technology for the production of biofuels but produces large amounts of process water. Therefore recirculation of process water from HTL of dried distillers grains with solubles (DDGS) is investigated. Two sets of recirculation on a continuous reactor system using K2CO3 as catalyst were carried out. Following this, the process water was recirculated in batch experiments for a total of 10 rounds. To assess the effect of alkali catalyst, non-catalytic HTL process water recycling was performed with 9 recycle rounds. Both sets of experiments showed a large increase in bio-crude yields from approximately 35 to 55wt%. The water phase and bio-crude s les from all experiments were analysed via quantitative gas chromatography-mass spectrometry (GC-MS) to investigate their composition and build-up of organic compounds. Overall the results show an increase in HTL conversion efficiency and a lower volume, more concentrated aqueous by-product following recycling.
Publisher: Wiley
Date: 16-02-2016
Abstract: The energy landscape governing a new pressure-induced phase transition in the hydroquinone-formic acid clathrate is reported in which the host structure collapses, opening up the cavity channels within which the guest molecules migrate and order. The reversible isosymmetric phase transition causes significant changes in the morphology and the birefringence of the crystal. The subtle intermolecular interaction energies in the clathrate are quantified at varying pressures using novel model energies and energy frameworks. These calculations show that the high-pressure phase forms a more stable host network at the expense of less-stable host-guest interactions. The phase transition can be kinetically hindered using a nonhydrostatic pressure-transmitting medium, enabling the comparison of intermolecular energies in two polymorphic structures in the same pressure range. Overall this study illustrates a need for accurate intermolecular energies when analyzing self-assembly structures and supramolecular aggregates.
Publisher: International Union of Crystallography (IUCr)
Date: 05-1997
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7TA10859A
Abstract: Ag doping in β-Zn 4 Sb 3 leads to the enhanced thermoelectric figure-of-merit ( zT ) and improved high-temperature thermal stability.
Publisher: Elsevier BV
Date: 06-2017
Publisher: AMPCo
Date: 24-02-2021
DOI: 10.5694/MJA2.50968
Publisher: American Chemical Society (ACS)
Date: 10-12-2012
DOI: 10.1021/IC301918X
Abstract: We present a combined experimental and theoretical charge density study of the coordination polymer Zn(HCOO)(2)(H(2)O)(2), which serves as a nonmagnetic reference for the isostructural magnetic compounds containing 3d transition metals. The charge density has been modeled using the multipole formalism against a high-resolution single-crystal X-ray diffraction data set collected at 100 K. The theoretical model is based on periodic density functional theory calculations in the experimental geometry. To gauge the degree of systematic bias from the multipole model, the structure factors of the theoretical model were also projected into a multipole model and the two theoretical models are compared with the experimental results. All models, both experiment and theory, show that the Zn atom densities are highly spherical but show small accumulations of charge toward the negative ligands. The metal-ligand interactions are found to be primarily ionic, but there are subtle topological indications of covalent contributions to the bonds. The source function calculated at the bond critical points reveals a rather delocalized picture of the density in the bridging carboxylates, and this presumably reflects the exchange pathway in the magnetic analogues.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C2CC37415C
Abstract: Powder diffraction is used to study thermal expansion properties of MOF-5 at moderate helium gas pressures: 1.7 bar (100-500 K) and 5-150 bar (150-300 K). The framework shows negative thermal expansion (NTE) at all pressures, but vibrational motions causing NTE are d ed with increasing pressures, leading to decreased NTE.
Publisher: American Chemical Society (ACS)
Date: 19-03-2021
Publisher: Wiley
Date: 30-01-2004
Publisher: Springer Science and Business Media LLC
Date: 18-11-2021
DOI: 10.1038/S41467-021-27007-Y
Abstract: Structural disorder, highly effective in reducing thermal conductivity, is important in technological applications such as thermal barrier coatings and thermoelectrics. In particular, interstitial, disordered, diffusive atoms are common in complex crystal structures with ultralow thermal conductivity, but are rarely found in simple crystalline solids. Combining single-crystal synchrotron X-ray diffraction, the maximum entropy method, diffuse scattering, and theoretical calculations, here we report the direct observation of one-dimensional disordered In 1+ chains in a simple chain-like thermoelectric InTe, which contains a significant In 1+ vacancy along with interstitial indium sites. Intriguingly, the disordered In 1+ chains undergo a static-dynamic transition with increasing temperature to form a one-dimensional diffusion channel, which is attributed to a low In 1+ -ion migration energy barrier along the c direction, a general feature in many other TlSe-type compounds. Our work provides a basis towards understanding ultralow thermal conductivity with weak temperature dependence in TlSe-type chain-like materials.
Publisher: American Chemical Society (ACS)
Date: 22-01-2018
Publisher: Springer Science and Business Media LLC
Date: 18-10-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CE01489E
Publisher: Wiley
Date: 22-06-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CE02358K
Abstract: Hydrothermal synthesis offers an environmentally benign method for synthesis of LiMn 2 O 4 anode material, but characterization is challenging due to structurally related impurity phases such as Li x Mn y O 2 and Mn 3 O 4 , whose presence may explain the inconsistent properties in published literature.
Publisher: American Chemical Society (ACS)
Date: 16-06-2014
DOI: 10.1021/AM502089A
Abstract: Zn4Sb3 is among the cheapest high performance thermoelectric materials, and it is made of relatively nontoxic elements. Strong activities are aimed at developing commercial power generation modules based on Zn4Sb3 making it vital to develop fast reliable synthesis processes for high-quality material. Here direct synthesis and compaction of homogeneous phase-pure thermoelectric Zn4Sb3 by spark plasma sintering (SPS) has been developed. Compared with the traditional quench and press method, the complexity and process time of the new method is very significantly reduced (order of magnitude), making large-scale production feasible. A composition gradient is observed in the pellet along the axis of applied pressure and current. The homogeneity of the pressed pellets is studied as a function of the SPS parameters: sintering time, applied current, sintering temperature and applied pressure, and the mechanism behind the formation of the gradient is discussed. The key finding is that pure and homogeneous Zn4Sb3 pellets can be produced by adding an extra layer of elemental Zn foil to compensate the Zn migration.
Publisher: American Chemical Society (ACS)
Date: 05-06-2014
DOI: 10.1021/CM500934Z
Publisher: Wiley
Date: 14-11-2012
Abstract: magnified image The electron–phonon coupling in the Rashba‐split two‐dimensional electron gas near the surface of the topological insulator Bi 2 Se 3 is studied by temperature‐dependent angleresolved photoemission. The coupling strength is found to be rather weak, with an electron–phonon mass enhancement parameter $ \\lambda = 0.12(8). $ (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Wiley
Date: 24-09-2020
Publisher: IOP Publishing
Date: 15-11-2012
Publisher: Wiley
Date: 08-11-2007
Abstract: Three high-quality single-crystal X-ray diffraction data sets have been measured under very different conditions on a structurally simple, but magnetically complex, coordination polymer, [Mn(HCOO)(2)(H(2)O)(2)](infinity) (1). The first data set is a conventional 100(2) K Mo(Kalpha) data set, the second is a very high resolution 100(2) K data set measured on a second-generation synchrotron source, while the third data set was measured with a tiny crystal on a high brilliance third-generation synchrotron source at 16(2) K. Furthermore, the magnetic susceptibility (chi) and the heat capacity (C(p)) have been measured from 2 to 300 K on pressed powder. The charge density of 1 was determined from multipole modeling of the experimental structure factors, and overall there is good agreement between the densities obtained separately from the three data sets. When considering the fine density features, the two 100 K data sets agree well with each other, but show small differences to the 16 K data set. Comparison with ab initio theory suggests that the 16 K APS data set provides the most accurate density. Topological analysis of the metal-ligand bonding, experimental 3d orbital populations on the Mn atoms, and Bader atomic charges indicate quite ionic, high-spin metal atoms. This picture is supported by the effective moment estimated from the magnetization measurements (5.840(2) mu(B)), but it is at variance with earlier spin density measurements from polarized neutron diffraction. The magnetic ordering originates from superexchange involving covalent interactions with the ligands, and non-ionic effects are observed in the static deformation density maps as well as in plots of the valence shell charge concentrations. Overall, the present study provides a benchmark charge density that can be used in comparison with future metal formate dihydrate charge densities.
Publisher: International Union of Crystallography (IUCr)
Date: 2016
DOI: 10.1107/S2053273315018318
Abstract: Crystalline silicon is an ideal compound to test the current state of experimental structure factors and corresponding electron densities. High-quality structure factors have been measured on crystalline silicon with synchrotron powder X-ray diffraction. They are in excellent agreement with benchmark Pendellösung data having comparable accuracy and precision, but acquired in far less time and to a much higher resolution (sin θ/λ 1.7 Å −1 ). The extended data range permits an experimental modelling of not only the valence electron density but also the core deformation in silicon, establishing an increase of the core density upon bond formation in crystalline silicon. Furthermore, a physically sound procedure for evaluating the standard deviation of powder-derived structure factors has been applied. S ling statistics inherently account for contributions from photon counts as well as the limited number of diffracting particles, where especially the latter are particularly difficult to handle.
Publisher: Springer Science and Business Media LLC
Date: 24-12-2013
Publisher: American Chemical Society (ACS)
Date: 04-05-2023
Publisher: Wiley
Date: 25-04-2017
Abstract: The discovery of the ultra-high thermoelectric figure of merit of 2.6 in SnSe has drawn attention to other lead-free IV-VI orthorhombic semiconductors. GeSe has been predicted to possess thermoelectric performances comparable to SnSe. Here, a complete structural study is reported of GeSe with temperature by means of high-resolution synchrotron powder X-ray diffraction. In the orthorhombic phase, the evolution of the bond distances with temperature is shown to deviate significantly with respect to SnSe. Analysis of the chemical bonding within the Quantum Theory of Atoms in Molecules shows that GeSe is ionic with van der Waals interlayer interactions. The signature of the N shell lone pair of Ge is also evident from both the electron density Laplacian and the ELF topologies.
Publisher: American Chemical Society (ACS)
Date: 31-01-2013
DOI: 10.1021/JP310462G
Abstract: The bonded radii for more than 700 bonded pairs of atoms, comprising more than 50 oxide crystals, extracted from experimental and theoretical electron density distributions, are averaged and compared with the ionic radii for first, second, and third row atoms. At odds with the assumption of a "fixed" ionic radius of 1.40 Å for the oxide anion, the bonded radius for the anion, r(b)(O), decreases systematically from 1.40 to 0.65 Å as the electron density distribution of the atom is progressively polarized and contracted by its bonded interactions. The radii for the more electropositive metal atoms agree with the ionic radii when the electron density distribution of the anion is largely unpolarized by its bonded interactions. However, those for the more electronegative metal atoms are progressively larger than the ionic radii as the electron density distribution of the anion is progressively polarized and contracted along the bond vectors with decreasing bond length. The progressive decrease of r(b)(O) indicates that the compilation of sets of ionic radii, based on a fixed radius for the oxide anion, is problematic and impacts the accuracy of the ionic radii for the metal atoms. The assumption of a "fixed" radius for the anion, made in the derivation of sets of radii, not only results in unrealistic negative ionic radii for the more electronegative atoms but also in ionic radii that are as much as 0.5 Å smaller than the bonded radii, particularly for the more electronegative M atoms. The lack of agreement between the ionic and the bonded radii for the more shared bonded interactions is ascribed to the progressive increase in the polarization and contraction of the electron density of the oxide anion by the bonded interactions with a concomitant decrease in the radius of the anion, a factor that was largely neglected in the compilation of the ionic radii for fluoride, oxide, sulfide, and nitride crystals. The close agreement of the bonded radii and procrystal bonded radii is consistent with the argument that the chemical forces that govern the electron density distributions and bonded radii are largely atomic in nature, resulting in comparable electron density distributions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA03252E
Abstract: SnSe thin films were successfully grown using single-target magnetron sputtering. The SnSe thin film annealed at 700 K exhibits superior thermoelectric performance compared with previously reported SnSe films and polycrystalline SnSe bulk material.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC05190C
Abstract: With changing pH four different structural regions in Ga 3+ aqueous solutions are observed. In contrast the effects of different anions and concentrations are minimal.
Publisher: International Union of Crystallography (IUCr)
Date: 04-1998
DOI: 10.1107/S0108768197012007
Abstract: Synchrotron radiation diffraction measurements at 100 (5) K have been carried out on bis(4,4′-bromophenyl)-61,61-diyl methano fullerene C 60 using area detector technology. In order to obtain a satisfactory description of the data it is necessary to introduce both a twinning model of the crystal and a disorder model consisting of two different isomers of the title compound. The study provides the first solid-state characterization of a 6–5 isomer of a methano fullerene. For the 6–6 isomer the geometry is in good agreement with recent literature on methano fullerenes. Unfortunately, the present study cannot resolve the bond lengths in the transannular region. The fact that the structure can be solved from diffraction data measured on a minute poorly scattering crystal shows that the low-temperature single-crystal synchrotron radiation technique is an indispensable tool in chemical crystallography.
Publisher: Wiley
Date: 25-08-2017
Publisher: Wiley
Date: 12-06-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6TA03630A
Abstract: The orientation of the P2-Na x Co 0.7 Mn 0.3 O 2 ( x = 1.0) on the electrode and its nanosheet morphology might contribute to Na ion insertion/extraction and strain mitigation.
Publisher: Wiley
Date: 26-02-2014
Publisher: Elsevier BV
Date: 05-2014
Publisher: AIP Publishing
Date: 23-07-2012
DOI: 10.1063/1.4731764
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: American Physical Society (APS)
Date: 25-11-2003
Publisher: American Physical Society (APS)
Date: 25-11-2003
Publisher: IOP Publishing
Date: 19-02-2008
Publisher: International Union of Crystallography (IUCr)
Date: 16-02-2012
Publisher: American Chemical Society (ACS)
Date: 19-12-2014
DOI: 10.1021/CM503479H
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 09-2011
Publisher: Wiley
Date: 05-02-2007
Publisher: Springer Science and Business Media LLC
Date: 03-08-2022
Publisher: Elsevier BV
Date: 07-2001
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0CC04418K
Abstract: The title compound undergoes two order-disorder transitions between 15 and 299 K, dictated by ordering of the guest molecules in the host cages, and resulting in three related crystal structures. We anticipate behaviour of this kind to be widespread, and speculate that the concept of "the crystal structure" for in idual Dianin's clathrates may be elusive.
Publisher: Wiley
Date: 10-05-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CC03541J
Abstract: The effect of substituting linkers with electron-donating moieties for part of the conventional ones on the melting and glass transition behaviours of ZIF-62 was investigated by calorimetry and X-ray diffraction.
Publisher: Wiley
Date: 17-02-2017
Abstract: Anharmonic lattice vibrations govern heat transfer in materials, and anharmonicity is commonly assumed to be dominant at high temperature. The textbook cubic ionic defect‐free crystal CsCl is shown to have an unexplained low thermal conductivity at room temperature (ca. 1 W/(m K)), which increases to around 13 W/(m K) at 25 K. Through high‐resolution X‐ray diffraction it is unexpectedly shown that the Cs atomic displacement parameter becomes anharmonic at 20 K.
Publisher: International Union of Crystallography (IUCr)
Date: 06-2018
Publisher: American Chemical Society (ACS)
Date: 23-06-2014
DOI: 10.1021/NL501489M
Abstract: Topological insulators are guaranteed to support metallic surface states on an insulating bulk, and one should thus expect that the electronic transport in these materials is dominated by the surfaces states. Alas, due to the high remaining bulk conductivity, it is challenging to achieve surface-dominated transport. Here we use nanoscale four-point setups with a variable contact distance on an atomically clean surface of bulk-insulating Bi2Te2Se. We show that the transport at 30 K is two-dimensional rather than three-dimensional, that is, surface-dominated, and we find a surface state mobility of 390(30) cm(2) V(-1) s(-1) at 30 K at a carrier concentration of 8.71(7) × 10(12) cm(-2).
Publisher: American Physical Society (APS)
Date: 13-04-2005
Publisher: American Chemical Society (ACS)
Date: 16-12-2013
DOI: 10.1021/CM402366Y
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6QI00520A
Abstract: The structural stability of undoped and doped (Sb, Bi, Ca, Zn) Mg 2 Si 0.4 Sn 0.6 is investigated by high resolution synchrotron PXRD and related to measured physical properties, revealing a stabilizing effect of cation doping.
Publisher: Wiley
Date: 10-05-2017
DOI: 10.1111/JACE.14932
Publisher: American Physical Society (APS)
Date: 14-12-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC03714E
Abstract: Multicomponent molecular alloy crystals exhibit intriguing effects of tuning and quenching in their photoluminescence, suggesting ‘alloy-crystal engineering’ as a useful design strategy for molecular functional materials.
Publisher: AIP Publishing
Date: 22-08-2019
DOI: 10.1063/1.5107484
Abstract: Using first principles calculations, we study the conduction band alignment, effective mass, and Fermi surface complexity factor of n-type Mg3Sb2 – xBix (x = 0, 1, and 2) from the full ab initio band structure. We find that with an increase in the Bi content, the K and M band minima move away from the conduction band minimum CB1 while the singly-degenerate Г band minimum shifts rapidly downward and approaches the conduction band minimum. However, the favorable sixfold degenerate CB1 band minimum keeps dominating the conduction band minimum and there is no band crossing between the Г and CB1 band minima. In addition, we show that the connection of the CB1 carrier pockets with the energy level close to the band minimum M can strongly enhance the carrier pocket anisotropy and Fermi surface complexity factor, which is likely the electronic origin for the local maximum in the theoretical power factor. Our calculations also show that the density of states effective mass, Seebeck coefficient, and Fermi surface complexity factor decrease with an increase in the Bi content, which is unfavorable to the electrical transport. In contrast, reducing the conductivity effective mass with an increase in the Bi content is beneficial to the electrical transport by improving carrier mobility and weighted mobility as long as the detrimental bipolar effect is insignificant. As a result, in comparison with n-type Mg3Sb2, n-type Mg3SbBi shows higher power factors and a much lower optimal carrier concentration for the theoretical power factor at 300 K, which can be easily achieved by the experiment.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7SE00104E
Abstract: Hydrothermal liquefaction of 11 biomasses and their co-liquefaction mixtures show how product composition depends on feedstock biochemical components, while nitrogen and oxygen distribution is controlled by carbohydrate and protein interactions.
Publisher: American Chemical Society (ACS)
Date: 31-03-2010
DOI: 10.1021/EF901584T
Publisher: International Union of Crystallography (IUCr)
Date: 27-07-2017
Publisher: American Physical Society (APS)
Date: 29-03-2022
Publisher: American Physical Society (APS)
Date: 02-10-2019
Publisher: Elsevier BV
Date: 11-2005
Publisher: IOP Publishing
Date: 02-2009
Publisher: American Chemical Society (ACS)
Date: 21-07-2014
DOI: 10.1021/CM501681R
Publisher: Wiley
Date: 24-06-2019
Abstract: The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.
Publisher: Springer Science and Business Media LLC
Date: 30-11-2010
DOI: 10.1038/NCOMMS1131
Abstract: The surface of a topological insulator plays host to an odd number of linearly-dispersing Dirac fermions, protected against back-scattering by time-reversal symmetry. Such characteristics make these materials attractive not only for studying a range of fundamental phenomena in both condensed matter and particle physics, but also for applications ranging from spintronics to quantum computation. Here, we show that the single Dirac cone comprising the topological state of the prototypical topological insulator Bi(2)Se(3) can co-exist with a two-dimensional electron gas (2DEG), a cornerstone of conventional electronics. Creation of the 2DEG is tied to a surface band-bending effect, which should be general for narrow-gap topological insulators. This leads to the unique situation where a topological and a non-topological, easily tunable and potentially superconducting, metallic state are confined to the same region of space.
Publisher: American Chemical Society (ACS)
Date: 02-08-2012
DOI: 10.1021/NN3021822
Abstract: Rubidium adsorption on the surface of the topological insulator Bi(2)Se(3) is found to induce a strong downward band bending, leading to the appearance of a quantum-confined two-dimensional electron gas state (2DEG) in the conduction band. The 2DEG shows a strong Rashba-type spin-orbit splitting, and it has previously been pointed out that this has relevance to nanoscale spintronics devices. The adsorption of Rb atoms, on the other hand, renders the surface very reactive, and exposure to oxygen leads to a rapid degrading of the 2DEG. We show that intercalating the Rb atoms, presumably into the van der Waals gaps in the quintuple layer structure of Bi(2)Se(3), drastically reduces the surface reactivity while not affecting the promising electronic structure. The intercalation process is observed above room temperature and accelerated with increasing initial Rb coverage, an effect that is ascribed to the Coulomb interaction between the charged Rb ions. Coulomb repulsion is also thought to be responsible for a uniform distribution of Rb on the surface.
Publisher: Springer Science and Business Media LLC
Date: 25-01-2016
DOI: 10.1007/S00216-016-9321-6
Abstract: Hydrothermal liquefaction is a promising technique for the production of bio-oil. The process produces an oil phase, a gas phase, a solid residue, and an aqueous phase. Gas chromatography coupled with mass spectrometry is used to analyze the complex aqueous phase. Especially small organic acids and nitrogen-containing compounds are of interest. The efficient derivatization reagent methyl chloroformate was used to make analysis of the complex aqueous phase from hydrothermal liquefaction of dried distillers grains with solubles possible. A circumscribed central composite design was used to optimize the responses of both derivatized and nonderivatized analytes, which included small organic acids, pyrazines, phenol, and cyclic ketones. Response surface methodology was used to visualize significant factors and identify optimized derivatization conditions (volumes of methyl chloroformate, NaOH solution, methanol, and pyridine). Twenty-nine analytes of small organic acids, pyrazines, phenol, and cyclic ketones were quantified. An additional three analytes were pseudoquantified with use of standards with similar mass spectra. Calibration curves with high correlation coefficients were obtained, in most cases R (2) > 0.991. Method validation was evaluated with repeatability, and spike recoveries of all 29 analytes were obtained. The 32 analytes were quantified in s les from the commissioning of a continuous flow reactor and in s les from recirculation experiments involving the aqueous phase. The results indicated when the steady-state condition of the flow reactor was obtained and the effects of recirculation. The validated method will be especially useful for investigations of the effect of small organic acids on the hydrothermal liquefaction process.
Publisher: International Union of Crystallography (IUCr)
Date: 2018
DOI: 10.1107/S2052252517015548
Abstract: Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element–hydrogen distances, r ( X —H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r ( X —H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydrocarbon rubrene (orthorhombic 5,6,11,12-tetraphenyltetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element–hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM.
Publisher: International Union of Crystallography (IUCr)
Date: 11-2022
DOI: 10.1107/S2053273322009081
Abstract: The name of the third author of the article by Koch et al. [ Acta Cryst. (2021). A 77 , 611–636] is corrected.
Publisher: American Chemical Society (ACS)
Date: 08-01-2020
Publisher: Springer Science and Business Media LLC
Date: 02-06-2022
DOI: 10.1038/S41467-022-30742-5
Abstract: In spintronics, the two main approaches to actively control the electrons’ spin involve static magnetic or electric fields. An alternative avenue relies on the use of optical fields to generate spin currents, which can bolster spin-device performance, allowing for faster and more efficient logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin-splitting. To explore the optical manipulation of a material’s spin properties, we consider the Rashba effect. Using time- and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an optical excitation can tune the Rashba-induced spin splitting of a two-dimensional electron gas at the surface of Bi 2 Se 3 . We establish that light-induced photovoltage and charge carrier redistribution - which in concert modulate the Rashba spin-orbit coupling strength on a sub-picosecond timescale - can offer an unprecedented platform for achieving optically-driven spin logic devices.
Publisher: American Chemical Society (ACS)
Date: 21-10-2010
DOI: 10.1021/CM100469Y
Publisher: American Chemical Society (ACS)
Date: 09-09-2010
DOI: 10.1021/JP103212Z
Publisher: American Chemical Society (ACS)
Date: 11-2000
DOI: 10.1021/JA994162A
Publisher: The Royal Society
Date: 13-01-2021
DOI: 10.1098/RSOS.201779
Abstract: We report a comparison of different common synthetic strategies for preparation of Prussian blue analogues (PBA). PBA are promising as cathode material for a number of different battery types, including K-ion and Na-ion batteries with both aqueous and non-aqueous electrolytes. PBA exhibit a significant degree of structural variation. The structure of the PBA determines the electrochemical performance, and it is, therefore, important to understand how synthesis parameters affect the structure of the obtained product. PBA are often synthesized by co-precipitation of a metal salt and a hexacyanoferrate complex, and parameters such as concentration and oxidation state of the precursors, flow rate, temperature and additional salts can all potentially affect the structure of the product. Here, we report 12 different syntheses and compare the structure of the obtained PBA materials.
Publisher: Springer Science and Business Media LLC
Date: 18-08-2013
Publisher: American Physical Society (APS)
Date: 16-01-2004
Publisher: American Physical Society (APS)
Date: 22-03-2013
Publisher: The Electrochemical Society
Date: 2011
DOI: 10.1149/2.033202JES
Publisher: American Chemical Society (ACS)
Date: 03-2008
DOI: 10.1021/JA076152C
Abstract: The charge density of Co2(CO)6(HC[triple bond]CC6H10OH) (1) in the crystalline state has been determined using multipolar refinement of single-crystal X-ray diffraction data collected (i) with a synchrotron source at very low temperatures (15 K) and (ii) using a conventional source with the crystal at intermediate temperature (100 K). The X-ray charge density model is augmented by complete active space and density functional theory calculations. Topological analyses of the different charge distributions show that the two Co atoms are not bonded to each other in the quantum theory of atoms in molecules (QTAIM) sense of the word. However, the behavior of the source function and the total energy density indicate that there is some bond-like character in the Co-Co interaction. The bridging alkyne fragment provides an unusual bonding situation, with extremely small electron density differences between the two Co-C bond critical points and the "CoC2" ring critical point. Thus, the structure is close to a topological catastrophe point. Comparison of the results obtained from the two diffraction data sets and ab initio theory suggests that the topology of the experimental electron density in this special atomic environment is highly sensitive to subtle effects of measurement errors and potential shortcomings of the multipole model, or to effects of the crystal field. Thus, even the two identical molecules in the asymmetric unit show altered bonding patterns.
Publisher: American Chemical Society (ACS)
Date: 26-08-2019
DOI: 10.1021/ACS.JPCLETT.9B01460
Abstract: Solar-driven production of renewable energy (e.g., H
Publisher: Wiley
Date: 09-03-2020
Publisher: International Union of Crystallography (IUCr)
Date: 23-09-2014
DOI: 10.1107/S2052252514020181
Abstract: Accurate structural models of reaction centres in zeolite catalysts are a prerequisite for mechanistic studies and further improvements to the catalytic performance. The Rietveld/maximum entropy method is applied to synchrotron powder X-ray diffraction data on fully dehydrated CHA-type zeolites with and without loading of catalytically active Cu 2+ for the selective catalytic reduction of NO x with NH 3 . The method identifies the known Cu 2+ sites in the six-membered ring and a not previously observed site in the eight-membered ring. The sum of the refined Cu occupancies for these two sites matches the chemical analysis and thus all the Cu is accounted for. It is furthermore shown that approximately 80% of the Cu 2+ is located in the new 8-ring site for an industrially relevant CHA zeolite with Si/Al = 15.5 and Cu/Al = 0.45. Density functional theory calculations are used to corroborate the positions and identity of the two Cu sites, leading to the most complete structural description of dehydrated silicoaluminate CHA loaded with catalytically active Cu 2+ cations.
Publisher: American Chemical Society (ACS)
Date: 17-08-2006
DOI: 10.1021/CM061195Y
Publisher: Wiley
Date: 08-05-2007
Publisher: American Chemical Society (ACS)
Date: 14-09-2023
DOI: 10.1021/JACS.3C07334
Publisher: AIP Publishing
Date: 15-01-2012
DOI: 10.1063/1.3675512
Abstract: The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and ided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2σ/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.
Publisher: International Union of Crystallography (IUCr)
Date: 29-03-2017
DOI: 10.1107/S2052520616019235
Abstract: A variable-temperature single-crystal structural study of five valence tautomeric cobalt molecular complexes, Co II (3,5-DBSQ) 2 (DBPy) 2 (1), Co II (3,5-DBSQ) 2 (DBPy) 2 ·1.33C 7 H 8 (1 S ), Co II (3,5-DBSQ) 2 (DCPy) 2 ·C 7 H 8 (2 S ), Co II (3,5-DBSQ) 2 (TBPy) 2 (3) and Co II (3,5-DBSQ) 2 (TCPy) 2 (4) (S = toluene, 3,5-DBSQ = 3,5-di- tert -butylsemiquinonate, DBPy = 3,5-dibromopyridine, DCPy = 3,5-dichloropyridine, TBPy = 3,4,5-tribromopyridine and TCPy = 3,4,5-trichloropyridine) is reported. The re-crystallization of (1 S ) in toluene at 277 K resulted in a concomitant formation of a solvent-free polymorph, Co II (3,5-DBSQ) 2 (DBPy) 2 (1). Thermally induced valence tautomerism (VT) is observed only in (1 S ), (1) and (2 S ) [hs-Co II (3,5-DBSQ) 2 L 2 ↔ ls-Co III (3,5-DBSQ)(3,5-DBCat)L 2 (hs = high spin, ls = low spin, 3,5-DBCat = 3,5-di- tert -butylcatecholate)], whereas (3) and (4) remain locked in the hs-Co II (3,5-DBSQ) 2 state during cooling of the s le. Multi-temperature single-crystal studies demonstrate the change in cobalt coordination environment during the VT conversion. The non-solvated compound (1) shows a sharp VT transition ( T 1/2 ∼ 245 K with Δ T ∼ 10 K) from hs-Co II (3,5-DBSQ) 2 (DBPy) 2 to ls-Co III (3,5-DBSQ)(3,5-DBCat)(DBPy) 2 oxidation state, whereas the other polymorph with lattice solvent (1 S ) results in a broad transition ( T 1/2 ∼ 150 K with Δ T ∼ 100 K). This increase in the VT transition temperature for (1) relative to (1 S ) illustrates the effect of lattice solvent on the VT transition mechanism. Additionally, the influence of halogen substitutions on the pyridine ring is discussed with respect to observed VT behaviour in the studied compounds.
Publisher: Springer Science and Business Media LLC
Date: 12-02-2018
DOI: 10.1038/S41563-017-0012-2
Abstract: Van der Waals (vdW) solids have attracted great attention ever since the discovery of graphene, with the essential feature being the weak chemical bonding across the vdW gap. The nature of these weak interactions is decisive for many extraordinary properties, but it is a strong challenge for current theory to accurately model long-range electron correlations. Here we use synchrotron X-ray diffraction data to precisely determine the electron density in the archetypal vdW solid, TiS
Publisher: Wiley
Date: 17-06-2013
Publisher: Springer Science and Business Media LLC
Date: 2006
DOI: 10.1557/PROC-0945-FF07-05
Abstract: The stability of high performance thermoelectric Zn 4 Sb 3 has been studied, by using synchrotron powder diffraction to establish differences in phase transition temperatures of two s les. High resolution multi temperature diffraction data has been collected, with a time interval of 13 months, and the phase transition temperature was determined based on the results of Rietveld refinements. The refinements show a difference in transition temperature from data collected the first time till data collected the second time. Furthermore the s les showed impurity peaks after being exposed to air for 13 months, indicating that the s le decomposes over time.
Publisher: American Chemical Society (ACS)
Date: 22-05-2019
Publisher: AIP Publishing
Date: 04-2009
DOI: 10.1063/1.3099589
Abstract: Powder inelastic neutron scattering (INS) has been used to determine the guest atom “rattling” energy in thermoelectric clathrates Ba8YxGe46−x (Yx=Ni6,Cu6,Zn8,Ga16) under different applied conditions. Chemical pressure was exerted by the atomic substitution, and a physical pressure of 9 kbars was applied using a cl cell. The volume reduction induced by the physical pressure increases the energy of the guest atom rattling mode, but the local chemical environment in the cage also appears to have a similar effect. The guest atom energies were investigated as function of temperature, and softening of the guest atom modes was observed upon cooling the s le. Ba8Ga16Ge30 with holes (p-type) and electrons (n-type) as charge carriers reveal similar temperature behavior, suggesting anharmonic potentials of similar shape for the Ba guest atom independent of the charge carrier type. For Sr8Ga16Ge30 a much stronger anharmonic potential was observed compared with Ba8Ga16Ge30. The guest atom energies for Ba8YxGe46−x (Yx=Ni6,Cu6,Zn8) extracted from powder INS were compared with Einstein energies obtained from atomic displacement parameters determined from multitemperature single crystal x-ray diffraction. Additionally, the Ba8YxGe46−x (Yx=Ni6,Cu6,Zn8) s les were characterized with respect to their thermoelectric properties.
Publisher: Wiley
Date: 13-12-2012
Publisher: Springer Science and Business Media LLC
Date: 29-06-2011
DOI: 10.1557/JMR.2011.116
Publisher: International Union of Crystallography (IUCr)
Date: 18-08-2019
Publisher: International Union of Crystallography (IUCr)
Date: 06-2018
DOI: 10.1107/S2052252518006590
Abstract: Frustrated magnetic systems exhibit extraordinary physical properties, but quantification of their magnetic correlations poses a serious challenge to experiment and theory. Current insight into frustrated magnetic correlations relies on modelling techniques such as reverse Monte-Carlo methods, which require knowledge about the exact ordered atomic structure. Here, we present a method for direct reconstruction of magnetic correlations in frustrated magnets by three-dimensional difference pair distribution function analysis of neutron total scattering data. The methodology is applied to the disordered frustrated magnet bixbyite, (Mn 1− x Fe x ) 2 O 3 , which reveals nearest-neighbor antiferromagnetic correlations for the metal sites up to a range of approximately 15 Å. Importantly, this technique allows for magnetic correlations to be determined directly from the experimental data without any assumption about the atomic structure.
Publisher: Wiley
Date: 15-06-2009
Abstract: A general solution: In situ synchrotron X-ray scattering in a high-pressure pulsed injection reactor (see picture) shows that magnetite nucleation and growth are temporally separated. Gram-scale crystalline, pure phase, superparamagnetic magnetite nanoparticles were synthesized without surfactants in supercritical water in less than one hour using a laboratory-scale continuous-flow reactor.
Publisher: American Chemical Society (ACS)
Date: 29-01-2018
Publisher: American Chemical Society (ACS)
Date: 08-02-2022
DOI: 10.1021/ACS.NANOLETT.1C04384
Abstract: Radiotherapy is a well-established and important treatment for cancer tumors, and advanced technologies can deliver doses in complex three-dimensional geometries tailored to each patient's specific anatomy. A 3D dosimeter, based on optically stimulated luminescence (OSL), could provide a high accuracy and reusable tool for verifying such dose delivery. Nanoparticles of an OSL material embedded in a transparent matrix have previously been proposed as an inexpensive dosimeter, which can be read out using laser-based methods. Here, we show that Cu-doped LiF nanocubes (nano-LiF:Cu) are excellent candidates for 3D OSL dosimetry owing to their high sensitivity, dose linearity, and stability at ambient conditions. We demonstrate a scalable synthesis technique producing a material with the attractive properties of a single dosimetric trap and a single near-ultraviolet emission line well separated from visible-light stimulation sources. The observed transparency and light yield of silicone sheets with embedded nanocubes hold promise for future 3D OSL-based dosimetry.
Publisher: American Physical Society (APS)
Date: 29-04-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2TA09948A
Abstract: Operando X-ray scattering shows that segmentation of Zn 4 Sb 3 with ion-blocking interfaces significantly reduces its decomposition rates under thermoelectric working conditions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP01730D
Abstract: Structural disorder, cation defects and anisotropic microstrain is quantified in the deceptively simple rock salt lead chalcogenides, PbX (X = S, Se, Te), based on high-resolution synchrotron powder X-ray diffraction analysis.
Publisher: American Chemical Society (ACS)
Date: 08-2019
Publisher: International Union of Crystallography (IUCr)
Date: 24-06-2010
DOI: 10.1107/S0021889810019187
Abstract: Crystalline boehmite nanoparticles have been prepared in a few minutes from thermal decomposition of aluminium nitrate in near- and supercritical water. Highly anisotropic nanoparticles are formed under continuous flow conditions using T-piece mixing and a large size tube diameter. The shapes and sizes of the synthesized nanocrystals were determined from peak shape analysis of powder X-ray diffraction data. The crystallite morphology is pressure dependent, and the size increases with temperature for constant reaction time and pressure. The modelled crystallite sizes and anisotropic shapes are in good agreement with transmission electron microscopy studies. At lower synthesis pressures the boehmite crystallite morphology is a mixture of platelets and bar-shaped crystals. The bar-shaped crystals align into polycrystalline fibre-like long thin needles, which again align sidewise in bundles. At higher pressures, only the polycrystalline fibres are formed. Full conversion of dried boehmite to γ-Al 2 O 3 is observed after short-term heating to 773 K with an overall conservation of the morphology.
Publisher: Springer Science and Business Media LLC
Date: 14-03-2014
Publisher: International Union of Crystallography (IUCr)
Date: 10-03-2011
DOI: 10.1107/S0021889811006522
Abstract: In situ synchrotron powder X-ray diffraction (PXRD) is used to study the formation of LiFePO 4 nanoparticles during hydrothermal synthesis from LiOH, H 3 PO 4 , and two different iron precursors, FeSO 4 and (NH 4 ) 2 Fe(SO 4 ) 2 . Furthermore, the synthesis of Li(Fe 1− x Mn x )PO 4 ( x = 0.25, 0.50 and 0.75) from LiOH, H 3 PO 4 and FeSO 4 /MnSO 4 is studied. The reactions involve an unknown intermediate phase, which is not the previously observed intermediate NH 4 FePO 4 ·H 2 O. The intermediate phase quickly transforms into LiFePO 4 and Li(Fe 1− x Mn x )PO 4 even at rather low temperatures. The presence of ammonium enhances the formation of LiFePO 4 , and it also leads to a significant reduction in the concentration of Li–Fe antisite defects. The in situ PXRD technique allows one to follow the influence of time, temperature and manganese doping on the antisite defect concentration, and it is shown that even under supercritical conditions a reaction time of several minutes is required to suppress the defects. This makes flow synthesis of defect-free LiFePO 4 and Li(Fe 1− x Mn x )PO 4 nanoparticles challenging.
Publisher: Wiley
Date: 18-09-2009
Publisher: International Union of Crystallography (IUCr)
Date: 13-04-2023
DOI: 10.1107/S1600576723002339
Abstract: Understanding the nucleation and growth mechanisms of nanocrystals under hydro- and solvothermal conditions is key to tailoring functional nanomaterials. High-energy and high-flux synchrotron radiation is ideal for characterization by powder X-ray diffraction and X-ray total scattering in real time. Different versions of batch-type cell reactors have been employed in this work, exploiting the robustness of polyimide-coated fused quartz tubes with an inner diameter of 0.7 mm, as they can withstand pressures up to 250 bar and temperatures up to 723 K for several hours. Reported here are recent developments of the in situ setups available for general users on the P21.1 beamline at PETRA III and the DanMAX beamline at MAX IV to study nucleation and growth phenomena in solvothermal synthesis. It is shown that data suitable for both reciprocal-space Rietveld refinement and direct-space pair distribution function refinement can be obtained on a timescale of 4 ms.
Publisher: International Union of Crystallography (IUCr)
Date: 20-07-2019
Publisher: International Union of Crystallography (IUCr)
Date: 17-10-2013
DOI: 10.1107/S0108767313024458
Abstract: CoSb 3 is an ex le of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ∼0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host–guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co–Sb and Sb–Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb 3 framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.
Publisher: International Union of Crystallography (IUCr)
Date: 06-06-2020
DOI: 10.1107/S2052252520005977
Abstract: Defective half-Heusler systems X 1− x YZ with large amounts of intrinsic vacancies, such as Nb 1− x CoSb, Ti 1− x NiSb and V 1− x CoSb, are a group of promising thermoelectric materials. Even with high vacancy concentrations they maintain the average half-Heusler crystal structure. These systems show high electrical conductivity but low thermal conductivity arising from an ordered YZ substructure, which conducts electrons, while the large amounts of vacancies in the X substructure effectively scatters phonons. Using electron scattering, it was recently observed that, in addition to Bragg diffraction from the average cubic half-Heusler structure, some of these s les show broad diffuse scattering indicating short-range vacancy order, while other s les show sharp additional peaks indicating long-range vacancy ordering. Here it is shown that both the short- and long-range ordering can be explained using the same simple model, which assumes that vacancies in the X substructure avoid each other. The s les showing long-range vacancy order are in agreement with the predicted ground state of the model, while short-range order s les are quenched high-temperature states of the system. A previous study showed that changes in s le stoichiometry affect whether the short- or long-range vacancy structure is obtained, but the present model suggests that thermal treatment of s les should allow controlling the degree of vacancy order, and thereby the thermal conductivity, without changes in composition. This is important as the composition also dictates the amount of electrical carriers. Independent control of electrical carrier concentration and degree of vacancy order should allow further improvements in the thermoelectric properties of these systems.
Publisher: American Chemical Society (ACS)
Date: 11-08-1998
DOI: 10.1021/IC9715613
Abstract: Extensive synchrotron (28 K) and conventional sealed-tube (9 K) X-ray diffraction data have been collected on Th(S(2)PMe(2))(4). Modeling of the electron density of the complex shows the bonding is quite ionic with little diffuse f or d type bonding density. Furthermore a large polarization of the Th core is observed revealing some 5d-like involvement in the bonding. High-quality ab initio density functional calculations are not able to reproduce these features and instead predict rather covalent bonding with considerable 6d-5f mixing. The study suggests that this theoretical method exaggerates the covalent nature of actinide bonds. It is shown that the most direct measure of covalence-charge transfer and electron distributions-can be usefully estimated by X-ray diffraction even in this most unfavorable of cases, where many actinide core electrons are present. The use of very low temperature data is crucial in the study of heavy metal complexes in order to minimize systematic errors such as thermal diffuse scattering and anharmonicity. The fact that accurate synchrotron radiation diffraction data can be measured within days makes studies of compounds beyond the first transition series more frequently within reach.
Publisher: American Chemical Society (ACS)
Date: 16-11-2007
DOI: 10.1021/CM702247B
Publisher: Elsevier BV
Date: 2005
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6TC01000H
Abstract: Enhanced filler filling fractions and thermoelectric performance in rare-earth filled-skutterudites by using a new non-equilibrium synthesis approach.
Publisher: Wiley
Date: 13-12-2012
Publisher: Elsevier BV
Date: 12-2018
Publisher: International Union of Crystallography (IUCr)
Date: 05-08-2014
DOI: 10.1107/S2053273314098945
Abstract: We introduce a novel method for reconstructing nuclear density distributions (NDDs): Nuclear Enhanced X-ray Maximum Entropy Method (NEXMEM). NEXMEM offers an alternative route to experimental NDDs, exploiting the superior quality of synchrotron X-ray data compared to neutron data. The method was conceived to analyse local distortions in the thermoelectric lead chalcogenides, PbX (X = S, Se, Te). Thermoelectric materials are functional materials with the unique ability to interconvert heat and electricity, holding much promise for green energy solutions such as waste heat recovery. The extraordinary thermoelectric performance of binary lead chalcogenides has caused huge research activity, but the mechanisms governing their unexpected low thermal conductivity still remain a controversial topic. It has been proposed to result from giant anharmonic phonon scattering or from local fluctuating dipoles on the Pb site.[1,2] No macroscopic symmetry change are associated with these effects, rendering them invisible to conventional crystallographic techniques. For this reason PbX was until recently believed to adopt the ideal, undistorted rock-salt structure. In the present study, we investigate PbX using multi-temperature synchrotron powder X-ray diffraction data in combination with the maximum entropy method (MEM) and NEXMEM. In addition NEXMEM has been validated by testing against simulated powder diffraction data of PbTe with known displacements of Pb. The increased resolution of NEXMEM proved essential for resolving Pb-displacement of 0.2 Å in simulated data. The figure below shows Pb in the (100) plane for MEM, NEXMEM and the actual NDD of the test structure. Our findings outline the extent of disorder in lead chalcogenides, promoting our understanding of this class of high-performance thermoelectric materials. Furthermore we introduce NEXMEM which can be used for widespread characterization of subtle atomic features in crystals with unusual properties.
Publisher: International Union of Crystallography (IUCr)
Date: 2023
DOI: 10.1107/S2052252522011782
Abstract: Serial femtosecond crystallography for small-unit-cell systems has so far seen very limited application despite obvious scientific possibilities. This is because reliable data reduction has not been available for these challenging systems. In particular, important intensity corrections such as the partiality correction critically rely on accurate determination of the crystal orientation, which is complicated by the low number of diffraction spots for small-unit-cell crystals. A data reduction pipeline capable of fully automated handling of all steps of data reduction from spot harvesting to merged structure factors has been developed. The pipeline utilizes sparse indexing based on known unit-cell parameters, seed-skewness integration, intensity corrections including an overlap-based combined Ewald sphere width and partiality correction, and a dynamically adjusted post-refinement routine. Using the pipeline, data measured on the compound K 4 [Pt 2 (P 2 O 5 H 2 ) 4 ]·2H 2 O have been successfully reduced and used to solve the structure to an R 1 factor of ∼9.1%. It is expected that the pipeline will open up the field of small-unit-cell serial femtosecond crystallography experiments and allow investigations into, for ex le, excited states and reaction intermediate chemistry.
Publisher: American Chemical Society (ACS)
Date: 06-01-2007
DOI: 10.1021/CM062384J
Publisher: American Chemical Society (ACS)
Date: 05-2008
DOI: 10.1021/NN7002426
Abstract: Nanocrystalline ZrO(2) s les with narrow size distributions and mean particle sizes below 10 nm have been synthesized in a continuous flow reactor in near and supercritical water as well as supercritical isopropyl alcohol using a wide range of temperatures, pressures, concentrations and precursors. The s les were comprehensively characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS), and the influence of the synthesis parameters on the particle size, particle size distribution, shape, aggregation and crystallinity was studied. On the basis of the choice of synthesis parameters either monoclinic or tetragonal zirconia phases can be obtained. The results suggest a critical particle size of 5-6 nm for nanocrystalline monoclinic ZrO(2) under the present conditions, which is smaller than estimates reported in the literature. Thus, very small monoclinic ZrO(2) particles can be obtained using a continuous flow reactor. This is an important result with respect to improvement of the catalytic properties of nanocrystalline ZrO(2).
Publisher: Wiley
Date: 09-01-2019
Abstract: The concept of secondary building units (SBUs) is central to all science on metal-organic frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) analysis was used to probe UiO-66 formation under solvothermal conditions. The expected SBU-a hexanuclear zirconium cluster-is present in the metal salt precursor solution. Addition of organic ligands results in a disordered structure with correlations up to 23 Å, resembling crystalline UiO-66. Heating leads to fast cluster aggregation, and further growth and ordering results in the crystalline product. Thus, SBUs are present already at room temperature and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis.
Publisher: American Physical Society (APS)
Date: 03-2017
Publisher: Springer Netherlands
Date: 2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CC00603A
Abstract: A non-hydrostatic pressure induces ligand to metal charge transfer on the iron site of a 3d–4f photomagnetic material.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B918909B
Abstract: FeSb(2) was recently identified as a narrow-gap semiconductor with indications of strong electron-electron correlations. In this manuscript, we report on systematic thermoelectric investigation of a number of FeSb(2) single crystals with varying carrier concentrations, together with two isoelectronically substituted FeSb(2-x)As(x) s les (x = 0.01 and 0.03) and two reference compounds FeAs(2) and RuSb(2). Typical behaviour associated with narrow bands and narrow gaps is only confirmed for the FeSb(2) and the FeSb(2-x)As(x) s les. The maximum absolute thermopower of FeSb(2) spans from 10 to 45 mV/K at around 10 K, greatly exceeding that of both FeAs(2) and RuSb(2). The relation between the carrier concentration and the maximum thermopower value is in approximate agreement with theoretical predictions of the electron-diffusion contribution which, however, requires an enhancement factor larger than 30. The isoelectronic substitution leads to a reduction of the thermal conductivity, but the charge-carrier mobility is also largely reduced due to doping-induced crystallographic defects or impurities. In combination with the high charge-carrier mobility and the enhanced thermoelectricity, FeSb(2) represents a promising candidate for thermoelectric cooling applications at cryogenic temperatures.
Publisher: Wiley
Date: 03-08-2022
Abstract: Melamine is a precursor and building block for graphitic carbon nitride (g‐CN) materials, a group of layered materials showing great promise for catalytic applications. The synthetic pathway to g‐CN includes a polycondensation reaction of melamine by evaporation of ammonia. Melamine molecules in the crystal organize into wave‐like planes with an interlayer distance of 3.3 Å similar to that of g‐CN. Here we present an extensive investigation of the experimental electron density of melamine obtained from modelling of synchrotron radiation X‐ray single‐crystal diffraction data measured at 25 K with special focus on the molecular geometry and intermolecular interactions. Both intra‐ and interlayer structures are dominated by hydrogen bonding and π‐interactions. Theoretical gas‐phase optimizations of the experimental molecular geometry show that bond lengths and angles for atoms in the same chemical environment (C−N bonds in the ring, amine groups) differ significantly more for the experimental geometry than for the gas‐phase‐optimized geometries, indicating that intermolecular interactions in the crystal affects the molecular geometry. In the experimental crystal geometry, one amine group has significantly more sp 3 ‐like character than the others, hinting at a possible formation mechanism of g‐CN. Topological analysis and energy frameworks show that the nitrogen atom in this amine group participates in weak intralayer hydrogen bonding. We hypothesize that melamine condenses to g‐CN within the layers and that the unique amine group plays a key role in the condensation process.
Publisher: International Union of Crystallography (IUCr)
Date: 2015
DOI: 10.1107/S2053273314024103
Abstract: Subtle structural features such as disorder and anharmonic motion may be accurately characterized from nuclear density distributions (NDDs). As a viable alternative to neutron diffraction, this paper introduces a new approach named the nuclear-weighted X-ray maximum entropy method (NXMEM) for reconstructing pseudo NDDs. It calculates an electron-weighted nuclear density distribution (eNDD), exploiting that X-ray diffraction delivers data of superior quality, requires smaller s le volumes and has higher availability. NXMEM is tested on two widely different systems: PbTe and Ba 8 Ga 16 Sn 30 . The first compound, PbTe, possesses a deceptively simple crystal structure on the macroscopic level that is unable to account for its excellent thermoelectric properties. The key mechanism involves local distortions, and the capability of NXMEM to probe this intriguing feature is established with simulated powder diffraction data. In the second compound, Ba 8 Ga 16 Sn 30 , disorder among the Ba guest atoms is analysed with both experimental and simulated single-crystal diffraction data. In all cases, NXMEM outperforms the maximum entropy method by substantially enhancing the nuclear resolution. The induced improvements correlate with the amount of available data, rendering NXMEM especially powerful for powder and low-resolution single-crystal diffraction. The NXMEM procedure can be implemented in existing software and facilitates widespread characterization of disorder in functional materials.
Publisher: AIP Publishing
Date: 08-2011
DOI: 10.1063/1.3617419
Abstract: In materials science continuous flow supercritical fluid reactors are widely used for highly controlled synthesis of nanoparticles. The major limitation of continuous flow reactors is that the inherent distribution of residence times leads to broadening of the corresponding size distribution of the nanoparticles, and in addition it is not possible to carry out synthesis with very short or very long reaction times. Here, we report a new synthesis concept that we call pulsed synthesis, which removes the limitations of flow synthesis at the expense of a more complex reactor design and extensive computer control. Another limitation of flow synthesis is that it is largely a black box, where limited direct information is available of the specific chemical reactions taking place, the particle nucleation, the particle growth, etc. Such information is commonly obtained from in situ synchrotron and neutron scattering studies, but transfer of information from in situ studies with static reactors to laboratory flow reactor conditions is highly non-trivial. The new pulse reactor provides superior heating rates, arbitrary residence times with narrow distribution limited only by the pulse duration, and the ability of using the same reactor both for nanoparticle production and in situ synchrotron studies thus eliminating the need for transfer of in situ information to laboratory reactor designs.
Publisher: International Union of Crystallography (IUCr)
Date: 15-06-1993
Publisher: Wiley
Date: 11-2012
Publisher: Danish Chemical Society
Date: 1994
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6DT03459D
Abstract: Phase pure polycrystalline MnSb 2 O 4 was synthesised under hydrothermal conditions, and the crystal structure was studied using single crystal and synchrotron powder X-ray diffraction from 100–1000 K.
Publisher: American Medical Association (AMA)
Date: 2021
Publisher: AIP Publishing
Date: 02-09-2004
DOI: 10.1063/1.1781762
Abstract: We present neutron and synchrotron powder-diffraction investigations as well as ab initio calculations to elucidate delicate structural features in doped skutterudites. S les with assumed Fe doping were investigated (FeyCo4Sb12, y=0.4, 0.8, 1.0, and 1.6), as well as s les with formal Ni substitution (Co4−xNixSb12, x=0, 0.4, 0.8, and 1.2). The present study serves as a case story for the determination of fine structural details of thermoelectric skutterudites by diffraction methods in combination with ab initio calculations. We illustrate the problem of fluorescence in the conventional x-ray powder diffraction on the Fe-doped s les by a comparison with the neutron powder-diffraction data. On the series of the Ni-substituted s les, the neutron powder-diffraction data were collected to investigate the exact sitting of the Ni. The s le with the highest Ni substitution (Co2.8Ni1.2Sb12) was also used for high resolution, high-energy synchrotron powder diffraction measurements. These revealed that the s le consists of two skutterudite phases. A complete description of the Ni-substituted s les was obtained in tandem with ab initio calculations, which show that the system contains a Ni-rich (Co0.38Ni3.62Sb12) and a Ni-poor (Co3.76Ni0.24Sb12)) skutterudite phases.
Publisher: American Chemical Society (ACS)
Date: 11-10-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5DT00447K
Abstract: The effects of non-hydrostaticity in n -pentane-isopentane were overcome by annealing, and accurate crystal structures of Co 3 (dpa) 4 Cl 2 ·CH 2 Cl 2 were determined above 10 GPa.
Publisher: AIP Publishing
Date: 08-12-2000
DOI: 10.1063/1.1319351
Abstract: Variable-temperature synchrotron x-ray powder diffraction data from dehydrated Na6[Al6Si6O24] reveal a structural phase transition that involves both the commensurate ordering of the extra-framework Na cations and a one-dimensional incommensurate modulation of the framework. Peak splittings and superlattice reflections implicate an orthorhombically-distorted volume-doubled supercell at room temperature (a=12.9432 Å, b=12.8403 Å, and c=9.1372 Å) ∼(√a×√a×a). These data also included additional superlattice peaks associated with an incommensurate long-period modulation with τ=(3/2 1/2 1)/8.9. All unique orderings of the 12 Na cations among the 16 available sites of the commensurate supercell are enumerated. A unique solution is identified that minimizes the structural energy and accounts for the observed superlattice peaks. Rietveld analysis reveals a significant Pauling “partial-collapse” tilt angle in the cation-ordered phase, that appears to decrease with increasing temperature.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TA06544F
Abstract: The thermal stability of the high performance n-type Te-doped Mg 3 Sb 1.5 Bi 0.5 system is investigated.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2DT02739A
Abstract: Ge 1− x Sn x nanoparticles are interesting for many different optoelectronic devices, however, the synthesis normally involves highly inert conditions, making it less promising for industry implementation. Here, a new non-inert synthesis is presented.
Publisher: International Union of Crystallography (IUCr)
Date: 2020
DOI: 10.1107/S205225251901580X
Abstract: The application of thermoelectrics for energy harvesting depends strongly on operational reliability and it is therefore desirable to investigate the structural integrity of materials under operating conditions. We have developed an operando setup capable of simultaneously measuring X-ray scattering data and electrical resistance on pellets subjected to electrical current. Here, operando investigations of β-Zn 4 Sb 3 are reported at current densities of 0.5, 1.14 and 2.3 A mm −2 . At 0.5 A mm −2 no s le decomposition is observed, but Rietveld refinements reveal increased zinc occupancy from the anode to the cathode demonstrating zinc migration under applied current. At 1.14 A mm −2 β-Zn 4 Sb 3 decomposes into ZnSb, but pair distribution function analysis shows that Zn 2 Sb 2 units are preserved during the decomposition. This identifies the mobile zinc in β-Zn 4 Sb 3 as the linkers between the Zn 2 Sb 2 units. At 2.3 A mm −2 severe Joule heating triggers transition into the γ-Zn 4 Sb 3 phase, which eventually decomposes into ZnSb, demonstrating Zn ion mobility also in γ-Zn 4 Sb 3 under electrical current.
Publisher: American Physical Society (APS)
Date: 04-05-2017
Publisher: International Union of Crystallography (IUCr)
Date: 19-09-2014
DOI: 10.1107/S2053273314015599
Abstract: Accurate atomic displacement parameters (ADPs) are a good indication of high-quality diffraction data. Results from the newly commissioned time-of-flight Laue diffractometer TOPAZ at the SNS are presented. Excellent agreement is found between ADPs derived independently from the neutron and X-ray data emphasizing the high quality of the data from the time-of-flight Laue diffractometer.
Publisher: Springer Science and Business Media LLC
Date: 30-12-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3SC52977K
Abstract: The chemical bonding in the pyrite (left) and marcasite (right) polymorphs of FeS 2 is investigated by charge density analysis.
Publisher: International Union of Crystallography (IUCr)
Date: 13-06-2017
DOI: 10.1107/S2052252517005553
Abstract: The crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu 2− x Se is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu 2− x Se is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se–Cu layers with additional copper between every alternate layer. The structural changes during the peculiar zT enhancing phase transition mainly consist of changes in the inter-layer distance coupled with subtle Cu migration. Just prior to the transition the structure exhibits strong negative thermal expansion due to the reordering of Cu atoms, when approached from low temperatures. The phase transition is fully reversible and group–subgroup symmetry relations are derived that relate the low-temperature β-phase to the high-temperature α-phase. Weak superstructure reflections are observed and a possible Cu ordering is proposed. The structural rearrangement may have a significant impact on the band structure and the Cu rearrangement may also be linked to an entropy increase. Both factors potentially contribute to the extraordinary zT enhancement across the phase transition.
Publisher: Wiley
Date: 20-08-2004
Abstract: The experimental electron density of the high-performance thermoelectric material Zn4Sb3 has been determined by maximum entropy (MEM) analysis of short-wavelength synchrotron powder diffraction data. These data are found to be more accurate than conventional single-crystal data due to the reduction of common systematic errors, such as absorption, extinction and anomalous scattering. Analysis of the MEM electron density directly reveals interstitial Zn atoms and a partially occupied main Zn site. Two types of Sb atoms are observed: a free spherical ion (Sb3-) and Sb2(4-) dimers. Analysis of the MEM electron density also reveals possible Sb disorder along the c axis. The disorder, defects and vacancies are all features that contribute to the drastic reduction of the thermal conductivity of the material. Topological analysis of the thermally smeared MEM density has been carried out. Starting with the X-ray structure ab initio computational methods have been used to deconvolute structural information from the space-time data averaging inherent to the XRD experiment. The analysis reveals how interstitial Zn atoms and vacancies affect the electronic structure and transport properties of beta-Zn4Sb3. The structure consists of an ideal A12Sb10 framework in which point defects are distributed. We propose that the material is a 0.184:0.420:0.396 mixture of A12Sb10, A11BCSb10 and A10BCDSb10 cells, in which A, B, C and D are the four Zn sites in the X-ray structure. Given the similar density of states (DOS) of the A12Sb10, A11BCSb10 and A10BCDSb10 cells, one may electronically model the defective stoichiometry of the real system either by n-doping the 12-Zn atom cell or by p-doping the two 13-Zn atom cells. This leads to similar calculated Seebeck coefficients for the A12Sb10, A11BCSb10 and A10BCDSb10 cells (115.0, 123.0 and 110.3 microV K(-1) at T=670 K). The model system is therefore a p-doped semiconductor as found experimentally. The effect is dramatic if these cells are doped differently with respect to the experimental electron count. Thus, 0.33 extra electrons supplied to either kind of cell would increase the Seebeck coefficient to about 260 microV K(-1). Additional electrons would also lower sigma, so the resulting effect on the thermoelectric figure of merit of Zn4Sb3 challenges further experimental work.
Publisher: American Physical Society (APS)
Date: 11-10-2016
Publisher: International Union of Crystallography (IUCr)
Date: 14-11-2019
DOI: 10.1107/S2052520619012733
Abstract: Anatase TiO 2 (a-TiO 2 ) nanocrystals are vital in catalytic applications both as catalysts ( e.g. photodegradation) and as a carrier material ( e.g. NOx removal from exhaust). The synthesis of a-TiO 2 nanocrystals and their properties have been heavily scrutinized, but there exists a clear gap between the scientific literature, and the scale and price expectation of industrial application. Here it is demonstrated that the industrially most attractive Ti precursor, titanyl sulfate (TiOSO 4 ), can be combined with the green, scalable and fast supercritical flow method to produce phase pure and highly crystalline a-TiO 2 nanoparticles with high specific surface area. Control of the nanocrystal morphology is important since it is known that certain facets substantially promote catalytic activity. It is, however, in itself challenging to determine nanocrystal morphology to provide a rational basis for the synthesis control. Here we advocate the use of advanced Rietveld refinement of powder X-ray diffraction data including anisotropic size broadening models in aiding to establish the s le three-dimensional morphology. This relatively quick and robust method assists in overcoming the often encountered ambiguity inherent in two-dimensional to three-dimensional reconstruction of selected particle morphologies with transmission electron microscopy and tomography techniques.
Publisher: International Union of Crystallography (IUCr)
Date: 2022
DOI: 10.1107/S2053273321011840
Abstract: Powder diffraction and pair distribution function (PDF) analysis are well established techniques for investigation of atomic configurations in crystalline materials, and the two are related by a Fourier transformation. In diffraction experiments, structural information, such as crystallite size and microstrain, is contained within the peak profile function of the diffraction peaks. However, the effects of the PXRD (powder X-ray diffraction) peak profile function on the PDF are not fully understood. Here, all the effects from a Voigt diffraction peak profile are solved analytically, and verified experimentally through a high-quality X-ray total scattering measurement on Ni powder. The Lorentzian contribution to the microstrain broadening is found to result in Voigt-shaped PDF peaks. Furthermore, it is demonstrated that an improper description of the Voigt shape during model refinement leads to overestimation of the atomic displacement parameter.
Publisher: Wiley
Date: 16-10-2000
DOI: 10.1002/1521-3773(20001016)39:20<3613::AID-ANIE3613>3.0.CO;2-D
Publisher: Wiley
Date: 26-02-2016
Publisher: American Chemical Society (ACS)
Date: 28-10-2016
Publisher: American Chemical Society (ACS)
Date: 11-08-2011
DOI: 10.1021/CM201271D
Publisher: Elsevier BV
Date: 10-2008
Publisher: International Union of Crystallography (IUCr)
Date: 04-09-2023
Publisher: American Chemical Society (ACS)
Date: 23-11-2016
Publisher: International Union of Crystallography (IUCr)
Date: 05-08-2014
DOI: 10.1107/S2053273314085866
Abstract: Zinc oxide (ZnO) is a material of great scientific and industrial relevance and is used widely in a variety of applications. Synthesis of ZnO nanoparticles can be performed by a wide range of methods resulting in a tremendous variety of sizes and shapes. Different in situ characterization methods have been used to investigate the ZnO formation under various synthesis conditions these include numerous spectroscopic methods and small angle scattering. Common for these studies is that the primary focus has been to extract information on particle size and shape of ZnO, while a more rigorous microstructural and structural analysis has been lacking. Furthermore, the aforementioned studies have primarily been focused on soft chemical synthesis methods, at low temperatures and in non-aqueous media, thus omitting the widely used environmentally benign and versatile hydrothermal method. In the present work the formation of ZnO during hydrothermal synthesis has been followed using in situ powder X-ray diffraction (PXRD) combined with Rietveld refinement, thus enabling the extraction of crystallographic as well as microstructural information during the formation and growth of ZnO. Supporting ex situ syntheses and characterization by electron microcopy, high resolution PXRD and other techniques have been used to corroborate the findings from the in situ experiments. Mapping out a vast parameter space has led to a deeper understanding of the intricate mechanisms governing the nucleation and growth of ZnO nanoparticles during hydrothermal synthesis. Among the parameters studied were the influence of temperature, type of base used and the influence of different ionic salts as synthesis directing agents. The various synthesis parameters were found to influence the following structural and microstructural features: crystallite shape, morphology and size as well as the twin-fault concentration, degree of doping and crystallinity.
Publisher: American Chemical Society (ACS)
Date: 06-2022
DOI: 10.1021/ACS.INORGCHEM.2C00701
Abstract: A highly reproducible, simple, and inexpensive synthesis method for obtaining phase-pure thermochromic monoclinic VO
Publisher: Elsevier BV
Date: 12-2012
Publisher: JMIR Publications Inc.
Date: 23-03-2023
DOI: 10.2196/43537
Abstract: Journal articles describing randomized controlled trials (RCTs) and systematic reviews with meta-analysis of RCTs are not optimally reported and often miss crucial details. This poor reporting makes assessing these studies’ risk of bias or reproducing their results difficult. However, the reporting quality of diet- and nutrition-related RCTs and meta-analyses has not been explored. We aimed to assess the reporting completeness and identify the main reporting limitations of diet- and nutrition-related RCTs and meta-analyses of RCTs, estimate the frequency of reproducible research practices among these RCTs, and estimate the frequency of distorted presentation or spin among these meta-analyses. Two independent meta-research studies will be conducted using articles published in PubMed-indexed journals. The first will include a s le of diet- and nutrition-related RCTs the second will include a s le of systematic reviews with meta-analysis of diet- and nutrition-related RCTs. A validated search strategy will be used to identify RCTs of nutritional interventions and an adapted strategy to identify meta-analyses in PubMed. We will search for RCTs and meta-analyses indexed in 1 calendar year and randomly select 100 RCTs (June 2021 to June 2022) and 100 meta-analyses (July 2021 to July 2022). Two reviewers will independently screen the titles and abstracts of records yielded by the searches, then read the full texts to confirm their eligibility. The general features of these published RCTs and meta-analyses will be extracted into a research electronic data capture database (REDCap Vanderbilt University). The completeness of reporting of each RCT will be assessed using the items in the CONSORT (Consolidated Standards of Reporting Trials), its extensions, and the TIDieR (Template for Intervention Description and Replication) statements. Information about practices that promote research transparency and reproducibility, such as the publication of protocols and statistical analysis plans will be collected. There will be an assessment of the completeness of reporting of each meta-analysis using the items in the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) statement and collection of information about spin in the abstracts and full-texts. The results will be presented as descriptive statistics in diagrams or tables. These 2 meta-research studies are registered in the Open Science Framework. The literature search for the first meta-research retrieved 20,030 records and 2182 were potentially eligible. The literature search for the second meta-research retrieved 10,918 records and 850 were potentially eligible. Among them, random s les of 100 RCTs and 100 meta-analyses were selected for data extraction. Data extraction is currently in progress, and completion is expected by the beginning of 2023. Our meta-research studies will summarize the main limitation on reporting completeness of nutrition- or diet-related RCTs and meta-analyses and provide comprehensive information regarding the particularities in the reporting of intervention studies in the nutrition field. DERR1-10.2196/43537
Publisher: American Physical Society (APS)
Date: 30-01-2015
Publisher: Wiley
Date: 1982
DOI: 10.1113/JPHYSIOL.1982.SP014037
Abstract: 1. The role of extracellular HCO3- and H+ in the formation of primary saliva and its subsequent modification by the glandular ducts has been investigated in the isolated perfused mandibular salivary gland of the rabbit. 2. Variation of extracellular HCO3- concentration between 12.5 and 50.0 mmol/l was without effect on salivary flow rate or on Na+ and K+ excretion, even though salivary HCO3- (and Cl-) content altered with changes in the extracellular concentration of the two anions. 3. Complete replacement of perfusate HCO3- by Cl- reduced fluid secretion by 34% and almost abolished ductal Na+ absorption. However, when extracellular pH was controlled by replacing HCO3- with the hydrophilic HEPES buffer, fluid secretion but not ductal Na+ absorption was restored to normal. 4. Complete replacement of exogenous HCO3- with acetate increased fluid secretion by 110% and also stimulated ductal Na+ absorption. This effect did not appear to be related to changes in cell pH and remains unexplained. Acetate entered the saliva in concentrations comparable to those seen for HCO3- in control experiments. 5. Salivary secretion showed an almost linear dependence on extracellular pH, rising from 14% of control (pH 7.4) levels at pH 6.2 to 130% at pH 7.8. Ductal Na+ absorption showed similar pH dependence. 6. Carbonic anhydrase inhibitors did not affect fluid secretion rates (except when supramaximal doses of ACh were used to evoke secretion) but they did cause a large reduction in salivary HCO3- output. In glands perfused with acetate rather than HCO3-, carbonic anhydrase inhibitors had no effect on excretion of fluid, acetate or metabolically derived HCO3-. Duct perfusion studies suggested that the effect of the inhibitors on HCO3- output was at the site of primary secretion rather than at the ductal site of HCO3- transport.
Publisher: AIP Publishing
Date: 11-12-2006
DOI: 10.1063/1.2404612
Abstract: Five compacted s les of thermoelectric Zn4Sb3 have been prepared from the same synthesis batch by spark plasma sintering. Four s les were made from powder with a grain size & μm, and one s le from powder with grain size & μm. Thermoelectric properties were evaluated, and an apparent strong correlation with s le density is found. ZnSb impurity contents obtained from powder x-ray diffraction cannot explain the variation in properties, which the authors’ suggest may be caused by slight changes in Zn content. The results show that minute changes in s le compaction conditions can have a larger effect on ZT than doping.
Publisher: American Physical Society (APS)
Date: 03-06-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT00122A
Abstract: Metal functionalized nanoparticles potentially have improved properties e.g. in catalytic applications, but their precise structures are often very challenging to determine. Here we report a structural benchmark study based on tetragonal anatase TiO2 nanoparticles containing 0-2 wt% copper. The particles were synthesized by continuous flow synthesis under supercritical water-isopropanol conditions. Size determination using synchrotron PXRD, TEM, and X-ray total scattering reveals 5-7 nm monodisperse particles. The precise dopant structure and thermal stability of the highly crystalline powders were characterized by X-ray absorption spectroscopy and multi-temperature synchrotron PXRD (300-1000 K). The combined evidence reveals that copper is present as a dopant on the particle surfaces, most likely in an amorphous oxide or hydroxide shell. UV-VIS spectroscopy shows that copper presence at concentrations higher than 0.3 wt% lowers the band gap energy. The particles are unaffected by heating to 600 K, while growth and partial transformation to rutile TiO2 occur at higher temperatures. Anisotropic unit cell behavior of anatase is observed as a consequence of the particle growth (a decreases and c increases).
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4770124
Abstract: The implementation of the van der Pauw (VDP) technique for combined high temperature measurement of the electrical resistivity and Hall coefficient is described. The VDP method is convenient for use since it accepts s le geometries compatible with other measurements. The technique is simple to use and can be used with s les showing a broad range of shapes and physical properties, from near insulators to metals. Three instruments utilizing the VDP method for measurement of heavily doped semiconductors, such as thermoelectrics, are discussed.
Publisher: American Physical Society (APS)
Date: 08-04-2016
Publisher: American Chemical Society (ACS)
Date: 10-11-2014
DOI: 10.1021/IC501603X
Abstract: A combined experimental and theoretical electron density study of the shortest trichromium metal wire, Cr3(dpa)4Cl2·(C2H5OC2H5)(x)(CH2Cl2)(1-x) (1, dpa = bis(2-pyridyl)amido), is reported. High resolution X-ray diffraction data has been collected both at 100 K using a conventional X-ray source (DS1) and at 15 K using a synchrotron X-ray source (DS2). The linear chromium string is terminated by Cl(-) ions at both ends, and each Cr atom is also coordinated by four N atoms from bridging dpa ligands. The two Cr-Cr bond distances are unequal at 100 K (with d(Cr1-Cr2) being 0.029 Å shorter than d(Cr2-Cr3)) but at 15 K they are almost equal (0.002 Å difference). Analysis of the slightly elongated thermal ellipsoids of the Cr2 atom suggests that it is not due to disorder, but the presence of a shallow potential energy surface. Laplacian maps clearly show local valence shell charge concentration (VSCC) in the electron density along the bisector of the equatorial Cr-N bonds. Integration over the atomic basins indicates that Cr2 has smaller atomic charge and volume than Cr1 and Cr3. The topological characterization of the Cr-Cr bonds indicates partly covalent characters with electron density at the bond critical point of ∼0.3 e Å(-3) and negative total energy density. The delocalization index of Cr-Cr is 0.8 for Cr1-Cr2 and 0.08 for Cr1-Cr3. Second-order perturbation analysis shows high stabilization energy of the Cr-Cr bonds (E(2) ∼ 190 kcal mol(-1)). Delocalization indices and source function and natural bond orbital analyses are all indicative of localized Cr-Cr bonding interactions.
Publisher: Wiley
Date: 28-01-2016
Abstract: TiO2@SnO2 hybrid nanocomposites were successfully prepared in gram scale using a dual-stage hydrothermal continuous-flow reactor. Temperature and pH in the secondary reactor were found to selectively direct nucleation and growth of the secondary material into either heterogeneous nanocomposites or separate intermixed nanoparticles. At low pH, 2 nm rutile SnO2 nanoparticles were deposited on 9 nm anatase TiO2 particles the presence of TiO2 was found to suppress formation of larger SnO2 particles. At high pH SnO2 formed separate particles and no deposition on TiO2 was observed. Ball-milling of TiO2 and SnO2 produced no TiO2@SnO2 composites. This verifies that the composite particles must be formed by nucleation and growth of the secondary precursor on the TiO2 . High concentration of secondary precursor led to formation of TiO2 particles embedded in aggregates of SnO2 nanoparticles. The results demonstrate how nanocomposites may be produced in high yield by green chemistry.
Publisher: IOP Publishing
Date: 06-05-2010
DOI: 10.1088/0022-3727/43/20/205402
Abstract: FeSb 2 has a high potential for technological applications due to its colossal thermoelectric power, giant carrier mobility and large magnetoresistance. Earlier, growth of ⟨1 0 1⟩-textured FeSb 2 films on quartz (0 0 0 1) substrates has been reported. Here magnetron sputtering is used to obtain ⟨0 0 2⟩-textured FeSb 2 films by employing a pre-deposited FeSb 2 thin-film layer as template. The in-plane thermoelectric properties of FeSb 2 films with different orientations were studied and compared. The anisotropy of FeSb 2 is shown to have an important effect on the transport properties of FeSb 2 films. Orientation control of the FeSb 2 films could be significant for their property optimization and thus highlight their application potential.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6CC09415E
Abstract: A cooperative diffusion mechanism of sodium ions in layered P2 sodium transition metal oxide is observed by in operando powder X-ray diffraction.
Publisher: American Chemical Society (ACS)
Date: 28-06-2021
Publisher: International Union of Crystallography (IUCr)
Date: 31-03-2020
DOI: 10.1107/S2052252520003619
Abstract: In chemistry, stereochemically active lone pairs are typically described as an important non-bonding effect, and recent interest has centred on understanding the derived effect of lone pair expression on physical properties such as thermal conductivity. To manipulate such properties, it is essential to understand the conditions that lead to lone pair expression and provide a quantitative chemical description of their identity to allow comparison between systems. Here, density functional theory calculations are used first to establish the presence of stereochemically active lone pairs on antimony in the archetypical chalcogenide MnSb 2 O 4 . The lone pairs are formed through a similar mechanism to those in binary post-transition metal compounds in an oxidation state of two less than their main group number [ e.g. Pb(II) and Sb(III)], where the degree of orbital interaction (covalency) determines the expression of the lone pair. In MnSb 2 O 4 the Sb lone pairs interact through a void space in the crystal structure, and their their mutual repulsion is minimized by introducing a deflection angle. This angle increases significantly with decreasing Sb—Sb distance introduced by simulating high pressure, thus showing the highly destabilizing nature of the lone pair interactions. Analysis of the chemical bonding in MnSb 2 O 4 shows that it is dominated by polar covalent interactions with significant contributions both from charge accumulation in the bonding regions and from charge transfer. A database search of related ternary chalcogenide structures shows that, for structures with a lone pair (Sb X 3 units), the degree of lone pair expression is largely determined by whether the antimony–chalcogen units are connected or not, suggesting a cooperative effect. Isolated Sb X 3 units have larger X —Sb— X bond angles and therefore weaker lone pair expression than connected units. Since increased lone pair expression is equivalent to an increased orbital interaction (covalent bonding), which typically leads to increased heat conduction, this can explain the previously established correlation between larger bond angles and lower thermal conductivity. Thus, it appears that for these chalcogenides, lone pair expression and thermal conductivity may be related through the degree of covalency of the system.
Publisher: Elsevier BV
Date: 07-2016
Publisher: American Chemical Society (ACS)
Date: 14-09-2020
Publisher: Wiley
Date: 08-07-2018
Publisher: American Chemical Society (ACS)
Date: 04-2021
Publisher: American Chemical Society (ACS)
Date: 31-05-2008
DOI: 10.1021/JA8007215
Abstract: The charge density (CD) of coordination polymer Co3(C8H4O4)4(C4H12N)2(C5H11NO)3 (1) has been determined from multipole modeling of structure factors obtained from single-crystal synchrotron X-ray diffraction measurements at 16 K. The crystal structure formally contains a negatively charged framework with cations and neutral molecules in the voids. However, the CD suggests that the framework is close to neutral, and therefore qualitative conclusions based on formal charge counting, e.g., about guest inclusion properties, will be incorrect. There are considerable differences in the charge distributions of the three unique benzenedicarboxylic acid linkers, which are widely used in coordination polymers. This suggests that the electrostatic properties of coordination polymer cavities, and thereby their inclusion properties, are highly tunable. The electron density topology shows that the tetrahedrally coordinated Co atom has an atomic volume which is 15% larger than that of the octahedrally coordinated Co atom. The crystal structure has both ferromagnetic and antiferromagnetic interactions, but no direct metal-metal bonding is evidenced in the CD. The magnetic ordering therefore takes place through superexchange in the oxygen bridges and the aromatic linkers. Bonding analysis of the experimental CD reveals that two oxygen atoms, O(1) and O(11), have significant covalent contributions to the metal-ligand bonding, whereas all other oxygen atoms have closed-shell interactions with the metals. This indicates that these two oxygen atoms are the key mediators of the magnetic ordering.
Publisher: American Chemical Society (ACS)
Date: 11-03-2009
DOI: 10.1021/JA900385U
Abstract: Experimental charge density modeling of a magnesium dimer complex and subsequent topological analysis reveals the existence of a chemical bond between the two central Mg atoms. Analysis of the molecular system using the energy density, the source function, and several density profiles along the entire bond path portrays the bond as one between two monovalent Mg atoms containing significant covalent character.
Publisher: American Chemical Society (ACS)
Date: 03-08-2011
DOI: 10.1021/JP2041789
Abstract: The crystal structure of the β-polymorph of hydroquinone (β-HQ), the apohost of a large family of clathrates, is reported with a specific focus on intermolecular interactions and the electrostatic nature of its cavity. Hirshfeld surface analysis reveals subtle close contacts between two interconnecting HQ networks, and the local packing and related close contacts were examined by breakdown of the fingerprint plot. An experimental multipole model containing anisotropic thermal parameters for hydrogen atoms has been successfully refined against 15(2) K single microcrystal synchrotron X-ray diffraction data. The experimental electron density model has been compared with a theoretical electron density calculated with the molecule embedded in its own crystal field. Hirshfeld charges, interaction energies and the electrostatic potential calculated for both models are qualitatively in good agreement, but small differences in the electrostatic potential persist due to charge transfer from all hydrogen atoms to the oxygen atoms in the theoretical model. The electrostatic potential in the center of the cavity is positive, very shallow and highly symmetric, suggesting that the inclusion of polar molecules in the void will involve a balance between opposing effects. The electric field is by symmetry zero in the center of the cavity, increasing to a value of 0.0185 e/Å(2) (0.27 V/Å) 1 Å along the 3-fold axis and 0.0105 e/Å(2) (0.15 V/Å) 1 Å along the perpendicular direction. While these values are substantial in a macroscopic context, they are quite small for a molecular cavity and are not expected to strongly polarize a guest molecule.
Publisher: AIP Publishing
Date: 28-01-2019
DOI: 10.1063/1.5081819
Abstract: LaSb2 has a layered crystal structure along the c-axis with ∼2% difference between the in-plane orthorombic a and b axes. Here, we report on the thermal conductivity, electrical resistivity, and Seebeck coefficient from 10 to 300 K as well as the magnetoresistance at 10 K. Using the van der Pauw technique on single crystal s les, the in-plane electrical resistivity tensor has been measured and it is found to be isotropic. An anisotropic crystal structure may have isotropic properties, but in the present case, the isotropic nature stems from crystal imperfection. Single crystal X-ray diffraction provides evidence of a mixing of the in-plane a- and b-directions leading to observed diffraction intensity where systematic absences are expected. Whether the underlying structural mechanism is twinning or stacking faults is unknown, but it could be the origin of the previously observed charge density wave states, and it may also explain the high unsaturating linear magnetoresistance reported here. At ambient conditions, LaSb2 is found to be stable in air, with no sign of bulk degradation after 5 years of storage however, some change is observed in the amorphous background scattering.
Publisher: American Chemical Society (ACS)
Date: 22-07-2015
DOI: 10.1021/JACS.5B04838
Abstract: Homogeneous reaction precursors may be used to form several solid-state compounds inaccessible by traditional synthetic routes, but there has been little development of techniques that allow for a priori prediction of what may crystallize in a given material system. Here, the local structures of FeSbx designed precursors are determined and compared with the structural motifs of their crystalline products. X-ray total scattering and atomic pair distribution function (PDF) analysis are used to show that precursors that first nucleate a metastable FeSb3 compound share similar local structure to the product. Interestingly, precursors that directly crystallize to thermodynamically stable FeSb2 products also contain local structural motifs of the metastable phase, despite their compositional disagreement. While both crystalline phases consist of distorted FeSb6 octahedra with Sb shared between either two or three octahedra as required for stoichiometry, a corner-sharing arrangement indicative of AX3-type structures is the only motif apparent in the PDF of either precursor. Prior speculation was that local composition controlled which compounds nucleate from amorphous intermediates, with different compositions favoring different local arrangements and hence different products. This data suggests that local environments in these amorphous intermediates may not be very sensitive to overall composition. This can provide insight into potential metastable phases which may form in a material system, even with a precursor that does not crystallize to the kinetically stabilized product. Determination of local structure in homogeneous amorphous reaction intermediates from techniques such as PDF can be a valuable asset in the development of systematic methods to prepare targeted solid-state compounds from designed precursors.
Publisher: American Physical Society (APS)
Date: 08-10-2014
Publisher: American Chemical Society (ACS)
Date: 17-11-2006
DOI: 10.1021/JA063695Y
Abstract: Comprehensive single-crystal structural investigations of n- and p-type Ba8Ga16Ge30 have been carried out using multitemperature neutron and conventional X-ray diffraction as well as resonant synchrotron X-ray diffraction. The data show that the guest atom positions and dynamics are very similar in the two structures, although the barium atoms are slightly more displaced from the cage centers in the p-type structure than in the n-type structure (Deltad = 0.025 A). For both structures Fourier difference maps calculated from very high-resolution neutron diffraction data (sin theta/lambda > 2 A-1) show that the Ba nuclear density at lowest temperatures (15 K) is distributed in a torus around the crystallographic 6d site with maxima in the 24j positions. At room temperature the maxima have shifted to the 24k position. Analysis of atomic displacement parameters give Einstein temperatures of approximately 60(1) K for both structures. Thus, the fundamental difference in the low temperature thermal conductivity observed for p- and n-type Ba8Ga16Ge30 appear not to be directly related to the guest atom behavior as is commonly assumed in thermoelectric research. The neutron data and the resonant synchrotron X-ray data facilitate refinement of Ga/Ge framework occupancies. The Ga atoms have a clear preference for the 6c site with the preference being somewhat stronger for the n-type structure.
Publisher: International Union of Crystallography (IUCr)
Date: 15-03-2006
DOI: 10.1107/S0108768105042795
Abstract: Two isostructural metal organic framework (MOF) structures have been synthesized by solvothermal methods and examined by single-crystal X-ray diffraction. A microcrystal of 2C 4 H 12 N + [Co 3 (C 8 H 4 O 4 ) 4 ] 2− ·3C 5 H 11 NO (1) was investigated at T = 120 K using synchrotron radiation. 2C 4 H 12 N + [Zn 3 (C 8 H 4 O 4 ) 4 ] 2− ·3C 5 H 11 NO (2) was investigated at multiple temperatures ( T = 30, 100, 200 and 300 K) on a conventional diffractometer. The thermal expansion of the structure of (2) is anisotropic and along the a axis, which corresponds to the metal chain direction. The structures contain anionic frameworks with cations and solvent molecules trapped in the voids. The magnetic susceptibility ( χ ) and heat capacity ( C p ) have been measured from 1.8 to 350 K. Compound (1) orders ferromagnetically with a broad phase transition observed in C p at ∼ 6 K. The magnetic moment reaches a value of 3 µ B per Co at 2 K in a magnetic field of 9 T, and a Curie–Weiss fit to χ ( T ) gives an effective moment ( μ eff ) of 4.2 μ B and a Weiss temperature (θ) of 23 K. The exchange mechanism for the magnetic coupling is suggested to involve the Co—O—Co bridges in the in idual three-metal-atom subchains. The three-dimensional magnetism presumably is due to super-exchange through two out of the three unique C 8 H 4 O 4 linker molecules, which have the carboxylate and benzene π systems well aligned.
Publisher: Elsevier BV
Date: 09-2012
Publisher: American Chemical Society (ACS)
Date: 10-05-2016
Publisher: American Chemical Society (ACS)
Date: 10-12-2018
Abstract: The upconversion luminescence (UCL) of colloidal lanthanide-doped upconversion nanocrystals (UCNCs) can be improved either by precise encapsulation of the surface by optically inert shells around the core, by an alteration of the nearby environment via metal nanoparticles, or by a combination of both. Considering their potential importance in crystalline silicon photovoltaics, the present study investigates both effects for two-dimensional arrangements of UCNCs. Using excitation light of 1500 nm wavelength, we study the variation in the upconversion luminescence from an Er
Publisher: American Chemical Society (ACS)
Date: 08-1999
DOI: 10.1021/JP990898I
Publisher: American Chemical Society (ACS)
Date: 16-11-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1NR03044B
Abstract: In situ pair distribution function analysis is used to follow the nucleation and growth of hafnia nanocrystals, which is highly non-classical. This reiterates the importance of investigating the chemical nature of nucleation and growth processes.
Publisher: Wiley
Date: 21-11-2012
Abstract: Mixed-valence trinuclear carboxylates, [M(3)O(O(2)CR)(6)L(3)] (M = metal, L = terminal ligand), have small differences in potential energy between the configurations M(II)M(III)M(III)⇔M(III)M(II)M(III)⇔M(III)M(III)M(II), which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M(2+) and M(3+) sites (e.g., about 0.2 Å for Fe-O bond lengths). It is well-established that the electron transfer (ET) between the metal sites in these mixed-valence molecules is strongly dependent on temperature and on the specific crystal environment however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single-crystal X-ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298 K on three different crystals, we first unexpectedly found that our batch of Fe(3)O (O(2)CC(CH(3))(3))(6)(C(5)H(5)N)(3) (1) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130 K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C-H⋅⋅⋅π and π⋅⋅⋅π intermolecular interactions. Subsequent high-pressure single-crystal X-ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96 GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit-cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure.
Publisher: International Union of Crystallography (IUCr)
Date: 30-06-2021
DOI: 10.1107/S2052252521005479
Abstract: Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Such disordered crystals with distinct local structures have unique properties arising from both collective and localized behaviour. Different local orderings can exist with identical average structures, making their differences hidden to Bragg diffraction methods. Using high-quality single-crystal X-ray diffuse scattering the local order in thermoelectric half-Heusler Nb 1− x CoSb is investigated, for which different local orderings are observed. It is shown that the vacancy distribution follows a vacancy repulsion model and the crystal composition is found always to be close to x = 1/6 irrespective of nominal s le composition. However, the specific synthesis method controls the local order and thereby the thermoelectric properties thus providing a new frontier for tuning material properties.
Publisher: Elsevier BV
Date: 12-2017
Publisher: American Physical Society (APS)
Date: 24-07-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CY00177B
Abstract: Ru nanoparticles are prepared via solvothermal synthesis with allotropism control. Both fcc and hcp s les are active catalysts for the hydrogen evolution reaction, but the hcp s le is stable during 12 hour operation.
Publisher: American Chemical Society (ACS)
Date: 22-09-1998
DOI: 10.1021/JA980200Z
Publisher: CRC Press
Date: 09-12-2005
Publisher: Springer Science and Business Media LLC
Date: 11-05-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3TC01191G
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: American Chemical Society (ACS)
Date: 24-07-2017
Publisher: American Chemical Society (ACS)
Date: 24-05-2012
DOI: 10.1021/CM300642T
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6SC01580H
Abstract: The need for a new approach to describing nanoparticle nucleation and growth different from the classical models is highlighted. In and ex situ total scattering experiments combined with additional characterization techniques are used to unravel the chemistry dictating ZnWO4 formation.
Publisher: American Physical Society (APS)
Date: 29-07-2020
Publisher: American Physical Society (APS)
Date: 12-10-2001
Publisher: International Union of Crystallography (IUCr)
Date: 31-01-2017
DOI: 10.1107/S2052520616018412
Abstract: The structural phase transition accompanied by a Jahn–Teller switch has been studied over a range of H/D ratios in (NH 4 ) 2 [Cu(H 2 O) 6 ](SO 4 ) 2 (ACTS). In particular, single-crystal neutron diffraction investigations of crystals with deuteration in the range 50 to 82% are shown to be consistent with previous electron paramagnetic resonance (EPR) experiments exhibiting a phase boundary at 50% deuteration under ambient pressure. Polycrystalline s les show that the two phases can co-exist. In addition, single-crystal neutron and polycrystalline X-ray diffraction pressure experiments show a shift to lower pressure at 60% deuteration versus previous measurements at 100% deuteration.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B9NJ00463G
Publisher: Wiley
Date: 05-03-2014
Abstract: Solvothermal and hydrothermal synthesis, that is, synthesis taking place in a solvent at elevated temperature and pressure, is a powerful technique for the production of advanced energy materials as it is versatile, cheap, and environmentally friendly. However, the fundamental reaction mechanisms dictating particle formation and growth under solvothermal conditions are not well understood. In order to produce tailor-made materials with specific properties for advanced energy technologies, it is essential to obtain an improved understanding of these processes and, in this context, in situ studies are an important tool as they provide real time information on the reactions taking place. Here, we present a review of the use of powder diffraction and total scattering methods for in situ studies of synthesis taking place under solvothermal and hydrothermal conditions. The experimental setups used for in situ X-ray and neutron studies are presented, and methods of data analysis are described. Special attention is given to the methods used to extract structural information from the data, for ex le, Rietveld refinement, whole powder pattern modelling and pair distribution function analysis. Ex les of in situ studies are presented to illustrate the types of chemical insight that can be obtained.
Publisher: Elsevier BV
Date: 04-2011
Publisher: American Physical Society (APS)
Date: 24-08-2011
Publisher: American Physical Society (APS)
Date: 30-03-2018
Publisher: Wiley
Date: 16-09-2014
Publisher: International Union of Crystallography (IUCr)
Date: 16-11-2009
DOI: 10.1107/S0108768109045091
Abstract: Details of the complex bonding environment present in the molecular centre of an alkyne-bridged dicobalt complex have been examined using a combination of experimental and theoretical charge-density modelling for two compounds which share a central Co 2 C 2 tetrahedral moiety as their common motif. Topological analysis of the experimental electron density illustrates the problem of separating the Co—C bond-critical points (b.c.p.s) from the intervening ring-critical point (r.c.p.), due largely to the flat nature of the electron density in the CoC 2 triangles. Such a separation of critical points is immediately obtained from a topological analysis of the theoretical electron density as well as from the multipole-projected theoretical density however, the addition of random noise to the theoretical structure factors prior to multipole modelling leads to a failure in consistently distinguishing two b.c.p.s and one r.c.p. in such close proximity within the particular environment of this Co 2 C 2 centre.
Publisher: Wiley
Date: 26-11-2010
Publisher: Wiley
Date: 15-05-2013
Publisher: American Chemical Society (ACS)
Date: 12-05-2014
DOI: 10.1021/JP501229P
Publisher: International Union of Crystallography (IUCr)
Date: 22-08-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CP04693E
Abstract: AuPd shell–Au core promoters with controlled shell thickness supported on titanium dioxide improve the photocatalytic hydrogen production.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4EE01320D
Abstract: In this review we discuss considerations regarding the common techniques used for measuring thermoelectric transport properties necessary for calculating the thermoelectric figure of merit, zT .
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6TA08316A
Abstract: Ag doping in Mg 3 Sb 2 leads to an enhanced average figure-of-merit ( zT ) by simultaneously improving the power factor and thermal conductivity.
Publisher: International Union of Crystallography (IUCr)
Date: 30-04-2019
DOI: 10.1107/S2053273319004820
Abstract: High-performing thermoelectric materials such as Zn 4 Sb 3 and clathrates have atomic disorder as the root to their favorable properties. This makes it extremely difficult to understand and model their properties at a quantitative level, and thus effective structure–property relations are challenging to obtain. Cu 2− x Se is an intensely studied, cheap and non-toxic high performance thermoelectric, which exhibits highly peculiar transport properties, especially near the β-to-α phase transition around 400 K, which must be related to the detailed nature of the crystal structure. Attempts to solve the crystal structure of the low-temperature phase, β-Cu 2− x Se, have been unsuccessful since 1936. So far, all studies have assumed that β-Cu 2− x Se has a three-dimensional periodic structure, but here we show that the structure is ordered only in two dimensions while it is disordered in the third dimension. Using the three-dimensional difference pair distribution function (3D-ΔPDF) analysis method for diffuse single-crystal X-ray scattering, the structure of the ordered layer is solved and it is shown that there are two modes of stacking disorder present which give rise to an average structure with higher symmetry. The present approach allows for a direct solution of structures with disorder in some dimensions and order in others, and can be thought of as a generalization of the crystallographic Patterson method. The local and extended structure of a solid determines its properties and Cu 2− x Se represents an ex le of a high-performing thermoelectric material where the local atomic structure differs significantly from the average periodic structure observed from Bragg crystallography.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2012
Publisher: Proceedings of the National Academy of Sciences
Date: 27-10-1998
Abstract: The electronic nature of low-barrier hydrogen bonds (LBHBs) in enzymatic reactions is discussed based on combined low temperature neutron and x-ray diffraction experiments and on high level ab initio calculations by using the model substrate benzoylacetone. This molecule has a LBHB, as the intramolecular hydrogen bond is described by a double-well potential with a small barrier for hydrogen transfer. From an “atoms in molecules” analysis of the electron density, it is found that the hydrogen atom is stabilized by covalent bonds to both oxygens. Large atomic partial charges on the hydrogen-bonded atoms are found experimentally and theoretically. Therefore, the hydrogen bond gains stabilization from both covalency and from the normal electrostatic interactions found for long, weak hydrogen bonds. Based on comparisons with other systems having short-strong hydrogen bonds or LBHBs, it is proposed that all short-strong and LBHB systems possess similar electronic features of the hydrogen-bonded region, namely polar covalent bonds between the hydrogen atom and both heteroatoms in question.
Publisher: International Union of Crystallography (IUCr)
Date: 10-1999
DOI: 10.1107/S0108768199004279
Abstract: The crystal structure of benzoylacetone (1-phenyl-1,3-butanedione, C 10 H 10 O 2 P 2 1 / c , Z = 4) has been determined at 300, 160 (both Mo K α X-ray diffraction, XRD), 20 (λ = 1.012 Å neutron diffraction, ND) and 8 K (Ag K α XRD), to which should be added earlier structure determinations at 300 (Mo K α XRD and ND, λ = 0.983 Å) and 143 K (Mo K α XRD). Cell dimensions have been measured over the temperature range 8–300 K a first- or second-order phase change does not occur within this range. The atomic displacement parameters have been analyzed using the thermal motion analysis program THMA 11. The most marked change in the molecular structure is in the disposition of the methyl group, which has a librational litude of ∼20° at 20 K and is rotationally disordered at 300 K. The lengths of the two C—O bonds in the cis -enol ring do not differ significantly, nor do those of the two C—C bonds, nor do these lengths change between 8 and 300 K. An ND difference synthesis (20 K) shows a single enol hydrogen trough (rather than two half H atoms), approximately centered between the O atoms analogous results were obtained by XRD (8 K). It is inferred that the enol hydrogen is in a broad, flat-bottomed single-minimum potential well between the O atoms, with a libration litude of ∼0.30 Å at 8 K. These results suggest that at 8 K the cis -enol ring in benzoylacetone has quasi-aromatic character, in agreement with the results of high-level ab initio calculations made for benzoylacetone [Schiøtt et al. (1998). J. Am. Chem. Soc. 120 , 12117–12124]. Application [in a related paper by Madsen et al. (1998). J. Am. Chem. Soc. 120 , 10040–10045] of multipolar analysis and topological methods to the charge density obtained from the combined lowest temperature X-ray and neutron data provides evidence for an intramolecular hydrogen bond with partly electrostatic and partly covalent character, and large p -delocalization in the cis -enol ring. This is in good agreement with what is expected from the observed bond lengths. Analysis of the total available (through the Cambridge Structural Database, CSD) population of cis -enol ring geometries confirms earlier reports of correlation between the degree of bond localization in the pairs of C—C and C—O bonds, but does not show the dependence of bond localization on d (O...O) that was reported earlier for a more restricted s le. It is suggested that the only reliable method of determining whether the enol hydrogen is found in a single or double potential well is by low-temperature X-ray or (preferably) neutron diffraction.
Publisher: Wiley
Date: 25-08-2017
Publisher: International Union of Crystallography (IUCr)
Date: 24-08-2018
DOI: 10.1107/S1600576718010531
Abstract: Layered transition metal oxides are of significant interest for applications in sodium-ion batteries. This article reports an operando powder X-ray diffraction study of the cathode material P 2-Na x Ni 0.3 Mn 0.7 O 2 during electrochemical cycling. The structural changes are shown to be reversible over two full cycles, and refinement of sodium occupancies provides insight into the very complex ion movement during battery operation. The sodium loading progresses through a set of metastable compositions showing that the working battery is out of equilibrium on a structural level. Peak broadening caused by stacking faults is observed in the P 2 structure at ∼4.0 V, prior to the ∼4.2 V phase transformation from P 2 to the ` Z ' phase
Publisher: Springer Science and Business Media LLC
Date: 04-09-2018
DOI: 10.1038/NCOMMS10892
Abstract: Thermoelectric technology, which possesses potential application in recycling industrial waste heat as energy, calls for novel high-performance materials. The systematic exploration of novel thermoelectric materials with excellent electronic transport properties is severely hindered by limited insight into the underlying bonding orbitals of atomic structures. Here we propose a simple yet successful strategy to discover and design high-performance layered thermoelectric materials through minimizing the crystal field splitting energy of orbitals to realize high orbital degeneracy. The approach naturally leads to design maps for optimizing the thermoelectric power factor through forming solid solutions and biaxial strain. Using this approach, we predict a series of potential thermoelectric candidates from layered CaAl 2 Si 2 -type Zintl compounds. Several of them contain nontoxic, low-cost and earth-abundant elements. Moreover, the approach can be extended to several other non-cubic materials, thereby substantially accelerating the screening and design of new thermoelectric materials.
Publisher: International Union of Crystallography (IUCr)
Date: 08-1995
DOI: 10.1107/S0108768194010360
Abstract: The electron-density distribution (EDD) of metallic beryllium has been derived from the structure factors of Larsen & Hansen [(1984). Acta Cryst. B40, 169-179] using the maximum entropy method (MEM). Subsequent topological analysis reveals non-nuclear maxima (NNM) in the EDD. Plots of the gradient field of the electron density illustrates this finding. A possible critical-point network for the hexagonal close-packed (h.c.p.) structure of beryllium is suggested. It is thus demonstrated that it is possible to obtain detailed topological information about the electron density in metallic beryllium without the use of a structural model. In order to test the findings of the MEM, the same set of structure factors were analysed using the multipole refinement method (MRM). Use of the MRM also reveals NNM. The results of the two different approaches to electron-density analysis are contrasted and discussed. Expressed within the framework of the theory of atoms in molecules, our results suggest that the h.c.p. structure of beryllium has no Be atoms directly bonded to other Be atoms. The structure is held together through a three-dimensional network of bonds between the NNM and Be atoms as well as between different NNM. The topological analysis thus reveals that the beryllium structure has important interactions connecting Be atoms of different basal plane layers. The breaking of these interactions when forming a surface may explain the abnormally large expansion of the inter-layer distance in the beryllium surface structure.
Publisher: American Physical Society (APS)
Date: 12-03-2001
Publisher: American Chemical Society (ACS)
Date: 10-10-2011
DOI: 10.1021/IC2015258
Abstract: Single crystal synchrotron X-ray diffraction measurements have been carried out on [Nd(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O (DMF = dimethyl-formamide), 1 [Y(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 2 [Ce(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 3 [Sm(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 4 [Tb(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 5 [Yb(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 6 and [Nd(DMF)(4)(H(2)O)(3)(μ-CN)Co(CN)(5)]·H(2)O, 7, at 15(2) K with and without UV illumination of the crystals. Significant changes in unit cell parameters are observed for all of the iron-containing complexes, while compound 7 shows no response to UV illumination. These results are consistent with previous results and are furthermore reproduced by powder synchrotron X-ray diffraction for compounds 1 and 7. Photoexcited crystal structures have been determined for 1-6 from refinements of two-conformer models, and excited state occupancies in the range 80-94% are found. Significant bond length changes are observed for the Fe-ligand bonds (up to 0.06 Å), the cyano bonds (up to 0.02 Å), and the lanthanide-ligand bonds (up to 0.1 Å). On the contrary, powder X-ray diffraction on the simple compound K(3)Fe(CN)(6), 8, upon UV illumination does not show any structural changes, suggesting that the photomagnetic effect requires the presence of both the transition metal and the lanthanide ion. Photomagnetic measurements show an increase in magnetization of the excited state of 1 of up to 3%, which is much diminished compared with previously published values of 45%. Furthermore, they show that the isostructural complex [La(DMF)(4)(H(2)O)(3)(μ-CN)Fe(CN)(5)]·H(2)O, 9, exhibits identical magnetic responses in the UV-induced excited crystal structure.
Publisher: Wiley
Date: 06-10-2023
Publisher: Springer Science and Business Media LLC
Date: 29-12-2009
Publisher: American Chemical Society (ACS)
Date: 20-02-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TA04110D
Abstract: A facile method is used to synthesise TiO 2 (B) for use in Li- and Na-ion batteries.
Publisher: American Physical Society (APS)
Date: 14-06-2011
Publisher: AIP Publishing
Date: 14-03-2013
DOI: 10.1063/1.4794816
Abstract: β-Zn4Sb3 is reported to have poor thermal stability and there is a wide scatter in the thermoelectric figure of merit (ZT) measured by different groups. Here, we show that both these issues are related to the zinc concentration. Specimens of β-Zn4Sb3 having different carrier concentrations (n) have been prepared and thermoelectric property measurements carried out between room temperature and 525 K. The maximum ZT is found to vary between 0.4 and 0.85. The cause of the large variation in ZT is the strong dependence of the lattice thermal conductivity (κL) on n which make ZT sensitive to small changes in zinc concentrations. Based on analytical calculations, we show that by changing the zinc interstitial to the zinc lattice ratio, it is possible to achieve the experimental κL variation. Thermal cycling of the electrical conductivity (σ) has been performed and phase identification after each cycling is carried out from power x-ray data. Different trends are observed in the specimens depending on n with accelerated degradation occurring only in a certain range of n (∼1.2–2.5 × 1020 cm−3) corresponding to low zinc content in the matrix.
Publisher: International Union of Crystallography (IUCr)
Date: 14-02-2013
DOI: 10.1107/S0021889813001295
Abstract: Monte Carlo (MC) methods, based on random updates and the trial-and-error principle, are well suited to retrieve form-free particle size distributions from small-angle scattering patterns of non-interacting low-concentration scatterers such as particles in solution or precipitates in metals. Improvements are presented to existing MC methods, such as a non-ambiguous convergence criterion, nonlinear scaling of contributions to match their observability in a scattering measurement, and a method for estimating the minimum visibility threshold and uncertainties on the resulting size distributions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/A908055D
Publisher: American Chemical Society (ACS)
Date: 28-10-1998
DOI: 10.1021/IC980556B
Abstract: The Fe-O and Fe-N bond lengths at two iron sites of the mixed-valence complex [Fe(3)O(OOCC(CH(3))(3))(6)(C(5)H(5)N)(3)] show a pronounced temperature dependence the bonds from two of the Fe atoms to the central oxygen atoms vary by more than 0.10 Å on cooling to 10 K whereas the bond from the third iron atom is essentially invariant. The variation is such that the longest Fe-O bonds at ambient temperature are the shorter ones at 10 K, with the crossover occurring at about 90 K. The bonds to the axial pyridine ligand show the opposite dependence. The variation is attributed to an equilibrium between different configurations, which interconvert through vibronic coupling, a process that involves electron transfer between the metal atoms. The position of the absorption edge for each of the iron atoms has been determined by resonance-diffraction experiments at the Fe K edge, performed at four different temperatures. At each temperature, the order of the absorption edges corresponds to that of the experimentally determined bond lengths. The crossover near 90 K is confirmed by the resonance experiments. The absorption-edge positions are related to the formal oxidation state by calibration with reference complexes of known oxidation state. The experiments demonstrate the close relation between the changes in coordination geometry and the oxidation states of the iron atoms.
Publisher: International Union of Crystallography (IUCr)
Date: 2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0JM02000A
Publisher: Royal Society of Chemistry (RSC)
Date: 12-08-2014
DOI: 10.1039/C4DT01307G
Abstract: In situ measurements of the hydrothermal formation of LiMn2O4 (LMO) nanocrystallites reveal that the reaction progresses in steps, each creating a different crystalline phase. The reaction route is summarized as KMnO4→disordered δ-MnO2→(ordered δ-MnO2)→LiMn2O4→(γ-Mn2O3)→Mn3O4. The phase purity of LMO can be controlled by reaction time and temperature where phase pure LMO is obtained after 150-210 seconds at 220 °C or 45-140 seconds at 260 °C. It is also concluded that production of phase pure LMO by this method comes at the price of reduced reaction yield. From the observed reaction route an alternative way to control the phase purity is proposed by changing the amount of reducing agent. This hypothesis is rejected by a set of in situ measurements showing that the reaction kinetics of subsequent reaction steps hinders the formation of phase pure LMO. From the observation of unit cell changes as function of the transformation from LMO to Mn3O4 three distinct reaction parts are observed. This indicates that the reaction is a solid-solid reaction with a phase boundary. The in situ measurements reveal that LMO first appears in the reaction solution as thin platelets with sizes ranging from 3-13 nm. As the reaction progresses the crystallites grow faster along the [111] direction giving rod-like shaped crystallites in the end. The LMO crystallites start off with the same shape at all temperatures investigated indicating that they form from δ-MnO2 crystallites.
Publisher: Wiley
Date: 17-06-2002
DOI: 10.1002/1521-3765(20020617)8:12<2775::AID-CHEM2775>3.0.CO;2-P
Publisher: Wiley
Date: 13-11-2020
Publisher: IEEE
Date: 09-2018
Publisher: AIP Publishing
Date: 17-04-2002
DOI: 10.1063/1.1466531
Abstract: Multitemperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba8Ga16Si30 are reported. For the framework atoms reciprocal space structural refinements give total occupancies in the unit cell of Ga/Si=3.8/2.2, 1.8/14.2, 10.2/13.8 for the 6c, 16i, and 24k sites respectively, thus showing that Ga avoids the tetrahedral 16i positions. The guest atom displacement parameters obtained from structure factor fitting are analyzed with semianharmonic Einstein models giving Einstein temperatures (ΘE) of 69(1), 98(7), and 124(2) K for Ba(2)(100), Ba(2)[100], and Ba(1), respectively. The analysis furthermore suggests that all guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures. The structure factors are subsequently used in the maximum entropy method calculations to obtain direct space nuclear densities. These are modeled with anharmonic one-particle potential models to fourth order. Even at elevated temperatures anharmonicity is limited indicating that the low thermal conductivity of the clathrate has a different origin.
Publisher: Springer Science and Business Media LLC
Date: 06-01-2017
DOI: 10.1038/NCOMMS13901
Abstract: Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg 3 Sb 1.5 Bi 0.5 , that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300−725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg 3 Sb 1.5 Bi 0.5 a promising candidate for the low- and intermediate-temperature thermoelectric applications.
Publisher: Elsevier BV
Date: 06-2011
Publisher: Springer Science and Business Media LLC
Date: 24-09-2014
Publisher: International Union of Crystallography (IUCr)
Date: 24-11-2017
DOI: 10.1107/S2052520617014044
Abstract: A multi-temperature structural study of Mg 2 Si and Mg 2 Sn was carried out from 100 to 700 K using synchrotron X-ray powder diffraction. The temperature dependence of the lattice parameters can be expressed as a = 6.3272 (4) + 6.5 (2) × 10 −5 T + 4.0 (3) × 10 −8 T 2 Å and a = 6.7323 (7) + 8.5 (4) × 10 −5 T + 3.8 (5) × 10 −8 T 2 Å for Mg 2 Si and Mg 2 Sn, respectively. The atomic displacement parameters (ADPs) are reported and analysed using a Debye model for the averaged U iso giving Debye temperatures of 425 (2) K for Mg 2 Si and 243 (2) K for Mg 2 Sn. The ADPs are considerably smaller for Mg 2 Si than for Mg 2 Sn reflecting the weaker chemical bonding in the Mg 2 Sn structure. Following the heating, an annealing effect is observed on the lattice parameters and peak widths in both structures, presumably due to changes in the crystal defects, but the lattice thermal expansion is almost unchanged by the annealing. This work provides accurate structural parameters which are of importance for studies of Mg 2 Si, Mg 2 Sn and their solid solutions.
Publisher: American Chemical Society (ACS)
Date: 11-1998
DOI: 10.1021/JA982317T
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6DT02323A
Abstract: The crystal structures of thermoelectric ZnSb and Zn 4 Sb 3 have been studied by high pressure single crystal X-ray diffraction and the pressure behavior is different from thermal response.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1TA09489K
Abstract: Using operando X-ray scattering and physical property measurements it is shown that PbS nanoinclusions in PbTe do not affect the high temperature thermal conductivity, and that improvements of hierarchical thermoelectrics have a complex origin.
Publisher: International Union of Crystallography (IUCr)
Date: 29-10-2021
DOI: 10.1107/S2053273321010159
Abstract: Data reduction and correction steps and processed data reproducibility in the emerging single-crystal total-scattering-based technique of three-dimensional differential atomic pair distribution function (3D-ΔPDF) analysis are explored. All steps from s le measurement to data processing are outlined using a crystal of CuIr 2 S 4 as an ex le, studied in a setup equipped with a high-energy X-ray beam and a flat-panel area detector. Computational overhead as pertains to data s ling and the associated data-processing steps is also discussed. Various aspects of the final 3D-ΔPDF reproducibility are explicitly tested by varying the data-processing order and included steps, and by carrying out a crystal-to-crystal data comparison. Situations in which the 3D-ΔPDF is robust are identified, and caution against a few particular cases which can lead to inconsistent 3D-ΔPDFs is noted. Although not all the approaches applied herein will be valid across all systems, and a more in-depth analysis of some of the effects of the data-processing steps may still needed, the methods collected herein represent the start of a more systematic discussion about data processing and corrections in this field.
Publisher: International Union of Crystallography (IUCr)
Date: 08-08-1996
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CE00544B
Abstract: The in situ PDF method provides detailed information about the formation and growth mechanisms of TiO 2 anatase nanoparticles under hydrothermal conditions.
Publisher: American Chemical Society (ACS)
Date: 19-05-2015
Publisher: American Chemical Society (ACS)
Date: 10-03-2015
DOI: 10.1021/JP511985D
Publisher: International Union of Crystallography (IUCr)
Date: 28-01-2021
DOI: 10.1107/S2053273320016605
Abstract: Powder X-ray diffraction has some inherent advantages over traditional single-crystal X-ray diffraction in accurately determining electron densities and structural parameters due to the lower requirements for s le crystallinity, simpler corrections and measurement simultaneity. For some simple inorganic materials, it has been shown that these advantages can compensate for disadvantages such as peak overlap and error-prone background subtraction. Although it is challenging to extend powder X-ray diffraction-based electron-density studies to organic materials with significant peak overlap, previous results using a dedicated vacuum diffractometer with a large image-plate camera (AVID) demonstrated that it can be done. However, the vacuum setup with the off-line detector system was found to prohibit a widespread use. Fast microstrip detectors, which have been employed at a number of powder diffraction beamlines, have the potential to facilitate electron-density studies. Nevertheless, no electron-density studies even for materials with slight peak overlap have been performed with microstrip detectors. One of the most critical problems has been a difference in sensitivity between microstrip channels, which substantially defines the dynamic range of a detector. Recently, a robust approach to this problem has been developed and applied to a total scattering measurement system (OHGI) with 15 MYTHEN microstrip modules. In the present study, synchrotron powder X-ray diffraction data obtained with OHGI are evaulated in terms of multipole electron densities and structural parameters (atomic positions and displacement parameters). These results show that, even without a dedicated setup and perfect s les, electron-density modelling can be carried out on high-quality powder X-ray diffraction data. However, it was also found that the required prior information about the s le prohibits widespread use of the method. With the presently obtainable data quality, electron densities of molecular crystals in general are not reliably obtained from powder data, but it is an excellent, possibly superior, alternative to single-crystal measurements for small-unit-cell inorganic solids. If aspherical atomic scattering factors can be obtained from other means (multipole databases, theoretical calculations), then atomic positions (including for hydrogen) and anisotropic atomic displacement parameters (non-hydrogen atoms) of excellent accuracy can be refined from synchrotron powder X-ray diffraction data on organic crystals.
Publisher: Wiley
Date: 24-09-2020
Publisher: International Union of Crystallography (IUCr)
Date: 22-05-2010
DOI: 10.1107/S0021889810014688
Abstract: The growing interest in inorganic nanoparticles for a wide range of applications is spurring a need for synthesis methods that allow a highly specific tailoring of material properties. Synthesis in supercritical fluids holds great promise for solving this problem, but so far the fundamental chemical processes taking place under these conditions are to a large extent unknown. Here the design, construction and application of a versatile experimental setup are reported this setup enables in situ synchrotron small-angle X-ray scattering/wide-angle X-ray scattering air distribution function (SAXS/WAXS/PDF) studies of the formation and growth of nanoparticles under supercritical fluid conditions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CY02307H
Abstract: Adding Fe to the PtPd nanocatalyst increases propene activity by forming more metallic Pt and PdO during synthesis and increasing Pt–Pd bond formation upon aging.
Publisher: International Union of Crystallography (IUCr)
Date: 02-1997
DOI: 10.1107/S0108768196011652
Abstract: A new structural model for the composite crystal bismuth strontium calcium cuprate [ M 2 Cu 2 O 3 ] 7+δ [CuO 2 ] 10 with M = Bi 0.06 Sr 0.46 Ca 0.48 and δ = 0.03 has been determined. The structure is orthorhombic with a = 11.380 (2), b = 12.960 (4) Å and incommensurate along c . Sublattice 1 of composition (CuO 2 ) 4 has c 1 = 2.7522 (4) Å and sublattice 2 of composition ( M 2 Cu 2 O 3 ) 4 has c 2 = 3.9155 (5) Å superspace group F 222(001 + γ)001 modulation vector q l = γ c 2* with γ = 0.7029 (2). The structural analysis has been based on 603 main reflections, 428 first-order and 64 second-order satellite reflections. The final residual is R = 0.0632 for all reflections, R = 0.0614 for main reflections, R = 0.0735 for first-order and R = 0.1084 for second-order satellite reflections λ = 0.6565 Å, μ = 19.4 mm −l The satellite reflections have been collected with X-ray synchrotron radiation. In this context, special experimental problems are discussed. It is shown that the true satellite reflections, which are the satellite reflections that are not also main reflections for one of the sublattices, are necessary in the least-squares refinement in order to avoid large correlations between displacive modulation litudes and thermal vibration litudes and thus to obtain a reasonable coordination chemistry.
Publisher: American Chemical Society (ACS)
Date: 20-04-2020
Publisher: Elsevier BV
Date: 11-2006
Publisher: Wiley
Date: 25-04-2019
Abstract: The covalent nature of the low-barrier N-H-N hydrogen bonds in the negative thermal expansion material H
Publisher: American Chemical Society (ACS)
Date: 30-04-2014
DOI: 10.1021/CG5000606
Publisher: International Union of Crystallography (IUCr)
Date: 2023
DOI: 10.1107/S2053273322010154
Abstract: The electron density and thermal motion of diamond are determined at nine temperatures between 100 K and 1000 K via synchrotron powder X-ray diffraction (PXRD) data collected on a high-accuracy detector system. Decoupling of the thermal motion from the thermally smeared electron density is performed via an iterative Wilson–Hansen–Coppens–Rietveld procedure using theoretical static structure factors from density functional theory (DFT) calculations. The thermal motion is found to be harmonic and isotropic in the explored temperature range, and excellent agreement is observed between experimental atomic displacement parameters (ADPs) and those obtained via theoretical harmonic phonon calculations (HPC), even at 1000 K. The Debye temperature of diamond is determined experimentally to be Θ D = 1883 (35) K. A topological analysis of the electron density explores the temperature dependency of the electron density at the bond critical point. The properties are found to be constant throughout the temperature range. The robustness of the electron density confirms the validity of the crystallographic convolution approximation for diamond in the explored temperature range.
Publisher: Springer Science and Business Media LLC
Date: 2002
Abstract: The orthorhombic clathrate compound Eu 4 Ga 8 Ge 16 orders antiferromagnetically at about 8 K. The magnetic structure is established by neutron powder diffraction while the thermal expansion and atomic displacement parameters are studied by synchrotron powder diffraction. The Eu spins align along the a -axis and achieve a zero-temperature magnetic moment equivalent to that of the free Eu 2+ ion. The thermal expansion is largest along the a -axis while the expansion along c has almost the same magnitude as that along b . The Eu displacement parameters display significant residual values at 0 K, largest in the c direction.
Publisher: American Chemical Society (ACS)
Date: 25-05-2022
Publisher: International Union of Crystallography (IUCr)
Date: 22-08-2016
DOI: 10.1107/S2052252516012707
Abstract: SnTe is a promising thermoelectric and topological insulator material. Here, the presumably simple rock salt crystal structure of SnTe is studied comprehensively by means of high-resolution synchrotron single-crystal and powder X-ray diffraction from 20 to 800 K. Two s les with different carrier concentrations (s le A = high, s le B = low) have remarkably different atomic displacement parameters, especially at low temperatures. Both s les contain significant numbers of cation vacancies (1–2%) and ordering of Sn vacancies possibly occurs on warming, as corroborated by the appearance of multiple phases and strain above 400 K. The possible presence of disorder and anharmonicity is investigated in view of the low thermal conductivity of SnTe. Refinement of anharmonic Gram–Charlier parameters reveals marginal anharmonicity for s le A , whereas s le B exhibits anharmonic effects even at low temperature. For both s les, no indications are found of a low-temperature rhombohedral phase. Maximum entropy method (MEM) calculations are carried out, including nuclear-weighted X-ray MEM calculations (NXMEM). The atomic electron densities are spherical for s le A , whereas for s le B the Te electron density is elongated along the 〈100〉 direction, with the maximum being displaced from the lattice position at higher temperatures. Overall, the crystal structure of SnTe is found to be defective and s le-dependent, and therefore theoretical calculations of perfect rock salt structures are not expected to predict the properties of real materials.
Publisher: Wiley
Date: 05-02-2007
Publisher: IEEE
Date: 2003
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7TA05788A
Abstract: Extremely low thermal conductivity and high thermoelectric performance are found in liquid-like Cu 2 Se 1−x S x polymorphic materials.
Publisher: IEEE
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 07-2022
Abstract: N-type Mg
Publisher: American Chemical Society (ACS)
Date: 06-10-2014
DOI: 10.1021/NN5044096
Abstract: The formation and growth of maghemite (γ-Fe2O3) nanoparticles from ammonium iron(III) citrate solutions (C(6)O(7)H(6) · xFe(3+) · yNH(4)) in hydrothermal synthesis conditions have been studied by in situ total scattering. The local structure of the precursor in solution is similar to that of the crystalline coordination polymer [Fe(H(2)cit(H2O)](n), where corner-sharing [FeO(6)] octahedra are linked by citrate. As hydrothermal treatment of the solution is initiated, clusters of edge-sharing [FeO(6)] units form (with extent of the structural order <5 Å). Tetrahedrally coordinated iron subsequently appears, and as the synthesis continues, the clusters slowly assemble into crystalline maghemite, giving rise to clear Bragg peaks after 90 s at 320 °C. The primary transformation from amorphous clusters to nanocrystallites takes place by condensation of the clusters along the corner-sharing tetrahedral iron units. The crystallization process is related to large changes in the local structure as the interatomic distances in the clusters change dramatically with cluster growth. The local atomic structure is size dependent, and particles smaller than 6 nm are highly disordered. The final crystallite size (<10 nm) is dependent on both synthesis temperature and precursor concentration.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5NR04459F
Abstract: An understanding of the nucleation and growth mechanism of bimetallic nanoparticles in solvothermal synthesis is important for further development of nanoparticles with tailored nanostructures and properties.
Publisher: IEEE
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 18-10-2016
Publisher: Wiley
Date: 24-07-2017
Abstract: Using quasi-simultaneous in situ PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNO
Publisher: International Union of Crystallography (IUCr)
Date: 17-06-2005
Publisher: American Chemical Society (ACS)
Date: 28-05-2015
Publisher: American Chemical Society (ACS)
Date: 31-08-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TC01611H
Abstract: ZnSb is a promising low cost, non-toxic thermoelectric material, but large scale applications require development of fast and easy synthesis methods.
Publisher: American Chemical Society (ACS)
Date: 07-09-2018
Publisher: Elsevier BV
Date: 04-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CP00820E
Abstract: Ruthenium arsenide is a very stable mineral inspired thermoelectric material with an attractive band structure but modest intrinsic performance.
Publisher: American Chemical Society (ACS)
Date: 05-2019
DOI: 10.1021/JACS.9B00043
Abstract: For many decades the lead chalcogenides PbTe, PbSe, and PbS (and their solid solutions) have been preferred high-performance thermoelectric materials due to their exceptional electronic and thermal properties as well as great stability during operation. However, there is a lack of understanding about the fundamental relation between the reported high-defect crystal structure containing cation disorder and vacancies and the observed transport properties, which follow expectations for an ideal rock salt crystal structure. Here we have studied a series of undoped lead sulfide s les (Pb
Publisher: International Union of Crystallography (IUCr)
Date: 17-12-2013
Publisher: BMJ
Date: 09-2022
DOI: 10.1136/BMJOPEN-2022-062139
Abstract: Australia has the highest incidence of melanoma in the world with variable care provided by a erse range of clinicians. Clinical quality registries aim to identify these variations in care and provide anonymised, benchmarked feedback to clinicians and institutions to improve patient outcomes. The Australian Melanoma Clinical Outcomes Registry (MelCOR) aims to collect population-wide, clinical-level data for the early management of cutaneous melanoma and provide anonymised feedback to healthcare providers. A modified Delphi process will be undertaken to identify key clinical quality indicators for inclusion in the MelCOR pilot. MelCOR will prospectively collect data relevant to these quality indicators, initially for all people over the age of 18 years living in Victoria and Queensland with a melanoma diagnosis confirmed by histopathology, via a two-stage recruitment and consent process. In stage 1, existing State-based cancer registries contact the treating clinician and provide an opportunity for them to opt themselves or their patients out of direct contact with MelCOR. After stage 1, re-identifiable clinical data are provided to the MelCOR under a waiver of consent. In stage 2, the State-based cancer registry will approach the patient directly and invite them to opt in to MelCOR and share identifiable data. If a patient elects to opt in, MelCOR will be able to contact patients directly to collect patient-reported outcome measures. Aggregated data will be used to provide benchmarked, comparative feedback to participating institutions/clinicians. Following the successful collection of pilot data, the feasibility of an Australia-wide roll out will be evaluated. Key quality indicator data will be the core of the MelCOR dataset, with additional data points added later. Annual reports will be issued, first to the relevant stakeholders followed by the public. MelCOR is approved by the Alfred Ethics Committee (58280/127/20).
Publisher: American Chemical Society (ACS)
Date: 20-01-2011
DOI: 10.1021/CG101271D
Publisher: American Physical Society (APS)
Date: 15-05-1999
Publisher: IEEE
Date: 2003
Publisher: IEEE
Date: 2005
Publisher: MDPI AG
Date: 24-11-2018
DOI: 10.3390/MA11122365
Abstract: In practice, there are some considerations to study stability, reliability, and output power optimization of a thermoelectric thin film operating dynamically. In this study stability and performance of a zinc antimonide thin film thermoelectric (TE) specimen is evaluated under transient with thermal and electrical load conditions. Thermoelectric behavior of the specimen and captured energy in each part of a thermal cycle are investigated. Glass is used as the substrate of the thin film, where the heat flow is parallel to the length of the thermoelectric element. In this work, the thermoelectric specimen is fixed between a heat sink exposed to the ambient temperature and a heater block. The specimen is tested under various electrical load cycles during a wide range of thermal cycles. The thermal cycles are provided for five different aimed temperatures at the hot junction, from 160 to 350 °C. The results show that the specimen generates approximately 30% of its total electrical energy during the cooling stage and 70% during the heating stage. The thin film generates maximum power of 8.78, 15.73, 27.81, 42.13, and 60.74 kW per unit volume of the thermoelectric material (kW/m3), excluding the substrate, corresponding to hot side temperature of 160, 200, 250, 300, and 350 °C, respectively. Furthermore, the results indicate that the thin film has high reliability after about one thousand thermal and electrical cycles, whereas there is no performance degradation.
Publisher: American Physical Society (APS)
Date: 25-08-2011
Publisher: Wiley
Date: 18-12-2022
Abstract: Magnetic materials with the spinel structure (A 2+ B 3+ 2 O 4 ) form the core of numerous magnetic devices, and ZnFe 2 O 4 constitutes a peculiar ex le where the nature of the magnetism is still unresolved. Susceptibility measurements revealed a cusp around T c = 13 K resembling an antiferromagnetic transition, despite the positive Curie–Weiss temperature determined to be Θ CW = 102.8(1) K. Bifurcation of field‐cooled and zero‐field‐cooled data below T c in conjunction with a frequency dependence of the peak position and a non‐zero imaginary component below T c shows it is in fact associated with a spin‐glass transition. Highly structured magnetic diffuse neutron scattering from single crystals develops between 50 K and 25 K revealing the presence of magnetic disorder which is correlated in nature. Here, the 3D‐mΔPDF method is used to visualize the local magnetic ordering preferences, and ferromagnetic nearest‐neighbor and antiferromagnetic third nearest‐neighbor correlations are shown to be dominant. Their temperature dependence is extraordinary with some flipping in sign and a strongly varying correlation length. The correlations can be explained by orbital interaction mechanisms for the magnetic pathways and a preferred spin cluster. This study demonstrates the power of the 3D‐mΔPDF method in visualizing complex quantum phenomena thereby providing a way to obtain an atomic‐scale understanding of magnetic frustration.
Publisher: Elsevier BV
Date: 07-2017
Publisher: Wiley
Date: 15-08-2012
Publisher: IEEE
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 19-07-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP01753G
Abstract: Destabilization of the type I clathrate Ba 8 Ga 16 Ge 30 at moderate temperatures has been revealed, prompting the thermoelectric community to consider the impact of operational temperatures on the stability and reliability of high zT materials.
Publisher: International Union of Crystallography (IUCr)
Date: 06-08-2011
Publisher: Author(s)
Date: 2016
DOI: 10.1063/1.4961902
Publisher: Wiley
Date: 05-12-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C1DT11523E
Abstract: The thermoelectric properties of a PtSb(2) single crystal containing a stoichiometric gradient were investigated. The gradient was produced by employing a Stockbarger synthesis technique. The gradient was observed through the use of spatial resolved Seebeck coefficient measurements and verified utilizing X-Ray Diffraction and Energy Dispersive X-Ray Spectroscopy. The correlation between Pt/Sb ratio and physical property parameters--Seebeck coefficient, mobility, resistivity and charge carrier concentration--was studied. Elemental analysis by Energy Dispersive X-Ray Spectroscopy, X-Ray Fluorescence and Inductively Coupled Plasma revealed Sb deficiency in the crystal, which explains the observed high charge carrier concentration and metallic properties. The transport properties were measured in the temperature range T = 20-300 K on a polycrystalline s le. Furthermore, ab initio theoretical calculations have been conducted to support the interpretation of the measurements.
Publisher: IOP Publishing
Date: 12-10-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CC42340A
Abstract: The effects of nano-sized TiO2 and ZnO ceramic inclusions on the high temperature stability of Zn4Sb3 have been studied using multi-temperature synchrotron powder X-ray diffraction. S les with 9 nm TiO2 nanoinclusions exhibit remarkable stability after three heating cycles to 625 K.
Publisher: IEEE
Date: 2005
Publisher: Elsevier BV
Date: 04-2016
Publisher: Wiley
Date: 14-02-2023
Abstract: Loosely bonded (“rattling”) atoms with s 2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X‐ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low‐lying transverse phonons dominated by large In 1+ z‐ axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In 1+ 5 s 2 lone pair electrons and Te 5 p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion.
Publisher: Wiley
Date: 17-02-2017
Abstract: Anharmonic lattice vibrations govern heat transfer in materials, and anharmonicity is commonly assumed to be dominant at high temperature. The textbook cubic ionic defect‐free crystal CsCl is shown to have an unexplained low thermal conductivity at room temperature (ca. 1 W/(m K)), which increases to around 13 W/(m K) at 25 K. Through high‐resolution X‐ray diffraction it is unexpectedly shown that the Cs atomic displacement parameter becomes anharmonic at 20 K.
Publisher: Elsevier BV
Date: 04-0020
Publisher: Wiley
Date: 31-03-2009
Publisher: American Chemical Society (ACS)
Date: 22-05-2015
Publisher: American Chemical Society (ACS)
Date: 18-03-2018
Publisher: Wiley
Date: 28-12-2010
Publisher: Springer Science and Business Media LLC
Date: 1999
DOI: 10.1557/PROC-590-145
Abstract: Recently materials with promising thermoelectric properties were discovered among the clathrates. Transport data has indicated that these materials have some of the characteristics of a good thermoelectric, namely a low thermal conductivity and a high electrical conductivity. Based on synchrotron powder and conventional single crystal x-ray diffraction data we have determined the charge density distribution in Sr 8 Ga 16 Ge 3O using the Maximum Entropy Method. The MEM density shows clear evidence of guest atom rattling, and this contributes to the reduction of the thermal conductivity. Analysis of the charge distribution reveals that Sr 8 Ga 16 Ge 30 contains mixed valence alkaline earth guest atoms. The Sr atoms in the small cavities are, as expected, doubly positively charged, whereas the Sr atoms in the large cavities appear negatively charged. The MEM density furthermore suggests that the Ga and Ge atoms may not be randomly disordered on the framework sites as found in the conventional leastsquares refinements.
Publisher: Wiley
Date: 06-03-2009
Abstract: X-ray vision: Single-crystal XRD experiments (see picture) reveal the excited-state structure of the photomagnetic heterobimetallic title complex. The system shows a decrease in all the iron-ligand bond lengths, suggesting that photoexcitation involves a ligand-to-metal charge transfer or a change in the superexchange coupling between the metal centers.
Publisher: IOP Publishing
Date: 11-09-2009
Publisher: Wiley
Date: 30-10-2009
Abstract: Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 degrees C) and supercritical (300 bar, 400 degrees C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small- and wide-angle X-ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)(3) within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate-determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub- and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub- and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X-ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 degrees C and gives a two-phase product of hydrated and non-hydrated aluminium oxide.
Publisher: International Union of Crystallography (IUCr)
Date: 03-10-2016
DOI: 10.1107/S2053273316012675
Abstract: Varying atomic short-range order is correlated with the ratio of the monoclinic ( m ) to tetragonal ( t ) phase in ZrO 2 nanoparticle formation by solvothermal methods. Reactions from Zr oxynitrate in supercritical methanol and Zr acetate in water (hydrothermal route) were studied in situ by X-ray total scattering. Irrespective of the Zr source and solvent, the structure of the precursor in solution consists of edge-shared tetramer chains. Upon heating, the nearest-neighbor Zr—O and Zr—Zr distances shorten initially while the medium-range connectivity is broken. Depending on the reaction conditions, the disordered intermediate transforms either rapidly into m -ZrO 2 , or more gradually into mixed m - and t -ZrO 2 with a concurrent increase of the shortest Zr—Zr distance. In the hydrothermal case, the structural similarity of the amorphous intermediate and m -ZrO 2 favors the formation of almost phase-pure m -ZrO 2 nanoparticles with a size of 5 nm, considerably smaller than the often-cited critical size below which the tetragonal is assumed to be favoured. Pair distribution function analysis thus unravels ZrO 2 phase formation on the atomic scale and in this way provides a major step towards understanding polymorphism of ZrO 2 beyond empirical approaches.
Publisher: International Union of Crystallography (IUCr)
Date: 18-08-2019
Publisher: American Chemical Society (ACS)
Date: 11-05-2021
Publisher: Springer Science and Business Media LLC
Date: 06-01-2017
DOI: 10.1038/NCOMMS13939
Abstract: Establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+ y Te, the parent compound of Fe 1+ y Se 1− x Te x superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+ y Te and thin films grown on the topological insulator Bi 2 Te 3 is canted out of the high-symmetry directions of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d -orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.
Publisher: Wiley
Date: 14-05-2014
Abstract: X-ray/neutron (X/N) diffraction data measured at very low temperature (15 K) in conjunction with ab initio theoretical calculations were used to model the crystal charge density (CD) of the host-guest complex of hydroquinone (HQ) and acetonitrile. Due to pseudosymmetry, information about the ordering of the acetonitrile molecules within the HQ cavities is present only in almost extinct, very weak diffraction data, which cannot be measured with sufficient accuracy even by using the brightest X-ray and neutron sources available, and the CD model of the guest molecule was ultimately based on theoretical calculations. On the other hand, the CD of the HQ host structure is well determined by the experimental data. The neutron diffraction data provide hydrogen anisotropic thermal parameters and positions, which are important to obtain a reliable CD for this light-atom-only crystal. Atomic displacement parameters obtained independently from the X-ray and neutron diffraction data show excellent agreement with a |ΔU| value of 0.00058 Å(2) indicating outstanding data quality. The CD and especially the derived electrostatic properties clearly reveal increased polarization of the HQ molecules in the host-guest complex compared with the HQ molecules in the empty HQ apohost crystal structure. It was found that the origin of the increased polarization is inclusion of the acetonitrile molecule, whereas the change in geometry of the HQ host structure following inclusion of the guest has very little effect on the electrostatic potential. The fact that guest inclusion has a profound effect on the electrostatic potential suggests that nonpolarizable force fields may be unsuitable for molecular dynamics simulations of host-guest interaction (e.g., in protein-drug complexes), at least for polar molecules.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1DT04001D
Abstract: Common methods for investigating the stability of thermoelectric materials are reviewed. A reporting protocol is proposed to streamline reporting of experimental parameters.
Publisher: American Scientific Publishers
Date: 08-2011
Publisher: Wiley
Date: 03-10-2014
Abstract: An unusual lithium lithiate [Li(diglyme)2][(diglyme)Li2(C4H3S)3], made up from three carbanions, two lithium cations, and a single donor base molecule in the anion and a single lithium cation, coordinated by two donor base molecules, is investigated in a combined study including X-ray diffraction, NMR spectroscopy and computational approaches in solution and the solid state. While the multicomponent lithiate is the only species present in the solid state, solution NMR spectroscopy and computational methods were employed to identify a second species in solution. The dimer [(diglyme)Li(C4H3S)]2 coexists with the lithiate in solution in a 1:1 ratio, the more the higher the polarity of the solvent is. Only the combination of this multitude of methods provides a firm picture of the whole.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CC09743F
Abstract: A green, fast, high-throughput, continuous-flow hydrothermal synthesis method is explored for preparation of silica coated nanoparticles with narrow size distribution.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CE25119A
Publisher: Informa UK Limited
Date: 11-1995
Publisher: IEEE
Date: 2003
Publisher: Wiley
Date: 02-10-2003
DOI: 10.1002/QUA.10791
Publisher: American Chemical Society (ACS)
Date: 16-08-2003
DOI: 10.1021/JA0346072
Abstract: The electron density distributions (EDD) of the redox active mixed valence trinuclear oxo-centered iron carboxylate, [Fe(3)O(CH(2)ClCOO)(6)(H(2)O)(3)].3H(2)O, 1, and the oxidized form of 1, [Fe(3)O(CH(2)ClCOO)(6)(H(2)O)(2)(CH(2)ClCOO)].1H(2)O, 2, as well as of [Fe(3)O(C(CH(3))(3)COO)(6) (NC(5)H(5))(3)], 3, have been determined from accurate single-crystal X-ray diffraction data measured at 100 K (1, 2) and from extensive synchrotron radiation X-ray diffraction data measured at 28 K (3). Analysis of the EDDs shows that the central oxygen atom has a very different EDD in the mixed valence complexes (1 and 3) compared with the oxidized complex (2). Furthermore, in 1 and 3 the chemical bonds between formally identical trivalent Fe atoms and the central oxygen are fundamentally different. This is in direct contrast to the Fe(IIImicro(3)-O) bonds in the oxidized complex, which are practically identical. Analysis of the d-orbital populations on the metal sites in the three complexes shows that the extra electron density on the Fe(II) site primarily is distributed in a d(yz) orbital (z-axis toward the central oxygen, y-axis perpendicular to the Fe(3)O-plane). Presence of extra charge in the d(yz) orbital correlates with a decrease in the d(xy) population, i.e., with a depletion of charge in the equatorial region of coordination to carboxylate oxygen. The d(xy) charge depletion appears to be of importance for determining the active versus trapped Fe(III) site, and the equatorial ligands therefore have a considerable influence on the ET process. Bader topological analysis of the EDDs corroborates the conclusions drawn from the orbital population analysis, but it also provides additional knowledge about the chemical bonding in the structures. For comparison with the X-ray results, theoretical calculations were carried out for 3 in the experimental geometry. The present information about ET processes in trinuclear oxo-centered iron complexes cannot be deduced from analysis of the molecular structures (i.e., bond lengths and angles), and thus it is demonstrated that X-ray charge density analysis is able to reveal subtle new features of significant physical and chemical importance on complex molecular systems.
Publisher: IEEE
Date: 2003
Publisher: International Union of Crystallography (IUCr)
Date: 11-04-2006
DOI: 10.1107/S1600536806011950
Abstract: The title compound, [Gd(C 4 H 9 NO) 4 (H 2 O) 3 ][Fe(CN) 6 ]·2H 2 O, is a bimetallic complex containing two isolated metal complexes. The Fe atom is bonded to six cyano ligands forming an almost ideal octahedron. One of the cyano groups is also connected through a hydrogen bond to a water molecule bonded to the Ga atom. Aside from three water molecules, gadolinium is also coordinated by four dimethylacetamide molecules, two of which show various degrees of structural disorder. The asymmetric unit also includes two solvent water molecules, which take part in hydrogen bonding, forming an extended network.
Publisher: American Chemical Society (ACS)
Date: 31-03-2017
Publisher: IOP Publishing
Date: 05-09-2022
Abstract: Micro four-point probing is a branch of electrical metrology where electrical (and electromagnetic) properties of charge carriers such as conductance, mobility, and tunneling magnetoresistance can be accurately and precisely determined at the μm scale and below. Here, we propose and demonstrate a novel application of micro four-point probe (M4PP) aimed at quantifying the thermoelectric properties of a s le. Specifically, we show that for an AC current passing through a bulk material at a low angular frequency ω , the voltage drop across the sensing electrodes at 2 ω is to first order proportional to the ratio ( α / κ ) of its Seebeck coefficient ( α ) to its thermal conductivity ( κ ). Verified by numerical simulations, our analytic theory is then put into practice on a suite of p- and n-type bulk semiconductors (Si, Ge, and BiTe). The M4PP estimates of the Seebeck coefficient in these materials are characterized both by high accuracy and precision, suggesting a novel in-situ metrology of thermoelectric properties at the µm scale.
Publisher: Wiley
Date: 26-02-2014
Abstract: Pair distribution function analysis of in situ total scattering data recorded during formation of WO3 nanocrystals under hydrothermal conditions reveal that a complex precursor structure exists in solution. The WO6 polyhedra of the precursor cluster undergo reorientation before forming the nanocrystal. This reorientation is the critical element in the formation of different hexagonal polymporphs of WO3.
Publisher: Wiley
Date: 23-03-2012
Abstract: Understanding nanoparticle-formation reactions requires multi-technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS)/total-scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria-stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y(2)O(3) equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub-nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit-cell dimensions. At yttria-doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time-resolved nanoparticle size distributions are calculated based on whole-powder-pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle-size distributions occur. In situ total scattering provides structural insight into the sub-nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six-coordinated zirconium atoms in the initial amorphous clusters to eight-coordinated zirconia atoms in stable crystallites. Representative s les prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.
Publisher: Wiley
Date: 12-02-2023
Abstract: Determination of crystal structures of nanocrystalline or amorphous compounds is a great challenge in solid‐state chemistry and physics. Pair distribution function (PDF) analysis of X‐ray or neutron total scattering data has proven to be a key element in tackling this challenge. However, in most cases, a reliable structural motif is needed as a starting configuration for structure refinements. Here, an algorithm that is able to determine the crystal structure of an unknown compound by means of an on‐the‐fly trained machine learning model, which combines density functional theory calculations with comparison of calculated and measured PDFs for global optimization in an artificial landscape, is presented. Due to the nature of this landscape, even metastable configurations and stacking disorders can be identified.
Publisher: American Chemical Society (ACS)
Date: 24-08-2011
DOI: 10.1021/JP2050405
Abstract: Analysis of accurate experimental and theoretical structure factors of diamond and silicon reveals that the contraction of the core shell due to covalent bond formation causes significant perturbations of the total charge density that cannot be ignored in precise charge density studies. We outline that the nature and origin of core contraction/expansion and core polarization phenomena can be analyzed by experimental studies employing an extended Hansen-Coppens multipolar model. Omission or insufficient treatment of these subatomic charge density phenomena might yield erroneous thermal displacement parameters and high residual densities in multipolar refinements. Our detailed studies therefore suggest that the refinement of contraction/expansion and population parameters of all atomic shells is essential to the precise reconstruction of electron density distributions by a multipolar model. Furthermore, our results imply that also the polarization of the inner shells needs to be adopted, especially in cases where second row or even heavier elements are involved in covalent bonding. These theoretical studies are supported by direct multipolar refinements of X-ray powder diffraction data of diamond obtained from a third-generation synchrotron-radiation source (SPring-8, BL02B2).
Publisher: AIP Publishing
Date: 12-01-2201
DOI: 10.1063/1.4827595
Abstract: While thermoelectric materials can be used for solid state cooling, waste heat recovery, and solar electricity generation, low values of the thermoelectric figure of merit, zT, have led to an efficiency too low for widespread use. Thermoelectric effects are characterized by the Seebeck coefficient or thermopower, which is related to the entropy associated with charge transport. For ex le, coupling spin entropy with the presence of charge carriers has enabled the enhancement of zT in cobalt oxides. We demonstrate that the coupling of a continuous phase transition to carrier transport in Cu2Se over a broad (360–410 K) temperature range results in a dramatic peak in thermopower, an increase in phonon and electron scattering, and a corresponding doubling of zT (to 0.7 at 406 K), and a similar but larger increase over a wider temperature range in the zT of Cu1.97Ag.03Se (almost 1.0 at 400 K). The use of structural entropy for enhanced thermopower could lead to new engineering approaches for thermoelectric materials with high zT and new green applications for thermoelectrics.
Publisher: Wiley
Date: 29-01-2020
Abstract: n-type Mg
Publisher: Wiley
Date: 31-03-2011
Publisher: Wiley
Date: 30-03-2011
Location: Brazil
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
Start Date: 2019
End Date: End date not available
Funder: The Velux Foundations
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