ORCID Profile
0000-0001-8040-3907
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Publisher: Wiley
Date: 06-06-2018
Abstract: Recent advances in high‐pressure technology provide access both to novel materials and to exotic properties of known materials, thus opening exciting opportunities for fundamental as well as applied research. This review summarizes for various classes of materials the existing knowledge on the thermoelectric behavior under hydrostatic pressure to identify promising directions for future developments.
Publisher: Wiley
Date: 2008
Abstract: This report used a 2 3 ‐factorial design to investigate the dependence of the reaction rate in the photocatalytic degradation of sodium lignosulfonate on solution pH, substrate concentration and TiO 2 catalyst dosage in a slurry reactor. The objective was to locate an optimum for the combination of these variables by using a suitable multiple‐linear regression model and to identify any interaction effects among the variables. The region of exploration selected for this study was: substrate concentration, 40 mg/L ‐ 60 mg/L catalyst dosage, 15 mg/L ‐ 35 mg/L and pH, 4‐8. A first‐order linear regression model could not adequately be fitted to the rate data, and the analysis of variance revealed significant interaction effects between pH and substrate concentration as well as pH and catalyst concentration. The nature of these interaction effects is discussed in detail. When a second‐order model was fitted to the data, an adequate description of the empirical relationship between the reaction rate and the three input variables was obtained. Analysis of the stationary point on the second‐order response surface revealed the existence of a saddle point within the region of exploration from where two near‐symmetric regions of high reaction rate were identified. The implications of these findings for practical reactor design are discussed.
Publisher: Springer Science and Business Media LLC
Date: 08-02-2018
DOI: 10.1557/ADV.2018.168
Publisher: American Physical Society (APS)
Date: 16-04-2009
Publisher: IOP Publishing
Date: 16-05-2014
DOI: 10.1088/0953-8984/26/23/235401
Abstract: We investigate the temperature response of the alkali-metal rattling modes in β-pyrochlores, AOs2O6 (A = K, Rb, Cs), from the results of ab initio molecular dynamics (MD) simulations performed at 20 K, 100 K and 300 K. Our results show that the temperature response of the T1u mode is clearly different from that of the T2g mode for all three pyrochlores. In this regard, two features are of particular note for both K and Rb (1) the T1u mode exhibits a distinctly stronger softening response with decreasing temperature compared to the T2g mode, and (2) the T1u mode becomes stronger and sharper with decreasing temperature. These two findings suggest that the T1u mode is significantly more anharmonic and sensitive to the cage dynamics than the T2g mode. Examination of the local potentials around the alkali-metal atoms reveals that K has the flattest and most anharmonic potential at all temperatures while Cs exhibits the narrowest potential. The temperature dependence of the local potentials reveals that, for K, the potential at a higher temperature is not a simple extrapolation to higher energy of that at a lower temperature. Instead, we find significant reconstruction of the potential at different temperatures. Finally, we explore the temperature response of the coupling between the alkali metals and find a complex temperature dependence which suggests that the origin of the coupling may be more complex than a pure Coulomb interaction. We also find an unexpected increase in the static disorder of the system at low temperatures for the K and Rb pyrochlores.
Publisher: American Chemical Society (ACS)
Date: 31-08-2021
Publisher: Elsevier BV
Date: 2022
Publisher: Springer Science and Business Media LLC
Date: 16-01-2023
DOI: 10.1038/S41524-022-00951-Z
Abstract: The application of machine learning models to predict material properties is determined by the availability of high-quality data. We present an expert-curated dataset of lithium ion conductors and associated lithium ion conductivities measured by a.c. impedance spectroscopy. This dataset has 820 entries collected from 214 sources entries contain a chemical composition, an expert-assigned structural label, and ionic conductivity at a specific temperature (from 5 to 873 °C). There are 403 unique chemical compositions with an associated ionic conductivity near room temperature (15–35 °C). The materials contained in this dataset are placed in the context of compounds reported in the Inorganic Crystal Structure Database with unsupervised machine learning and the Element Movers Distance. This dataset is used to train a CrabNet-based classifier to estimate whether a chemical composition has high or low ionic conductivity. This classifier is a practical tool to aid experimentalists in prioritizing candidates for further investigation as lithium ion conductors.
Publisher: Elsevier BV
Date: 05-2005
Publisher: Elsevier BV
Date: 2006
Publisher: Wiley
Date: 20-05-2021
Abstract: Exploring non‐precious metal‐based electrocatalysts at high current density and stability is an urgent issue for sustainable H 2 production. Here, hierarchical core‐shell N‐doped carbon encapsulated array‐like FeP 4 and CoP active components have been fabricated in situ on the surface of nickel foam (NC@FeP 4 ‐CoP/NF) by etching sheet‐like ZIF‐67 arrays, Prussian analog formation, and phosphating in turns. The crystallinity, hierarchical heterostructure, and chemical state have been carefully discussed. Electrochemical studies demonstrate that the catalyst displays excellent electrocatalytic activity and durability in electrochemical oxygen evolution reaction (η 20 = 218 mV) and hydrogen evolution reaction (η 10 = 116 mV), better than most previously reported bifunctional catalysts. Moreover, the bifunctional catalyst only needs 1.72 and 1.80 V cell voltages at 500 and 1000 mA cm −2 respectively, together with a good catalytic stability at 500 mA cm −2 for 48 h, implying potential commercialization prospects. This excellent electrocatalytic performance is mainly attributed to the distinctive hierarchical structure as well as core‐shell NC encapsulated FeP 4 ‐CoP active sites, which can enhance the charge transport rate, inhibit the exfoliation of the active materials, provide a larger active surface area, and facilitate electrolyte diffusion and gas release.
Publisher: IOP Publishing
Date: 31-10-2013
DOI: 10.1088/0953-8984/25/47/475404
Abstract: We have used ab initio molecular dynamics simulations validated against inelastic neutron scattering data to study alkali-metal dynamics in the β-pyrochlore osmates AOs2O6 (A=K, Rb, Cs) at 300 K to gain insight into the microscopic nature of rattling dynamics in these materials. Our results provide new evidence at the microscopic level for rattling dynamics: (1) the elemental magnitude spectra calculated from the MD show a striking dominance by the alkali metals at low energies indicating weak coupling to the cage, (2) the atomic root-mean-square displacements for the alkali metals are significantly larger than for the other atoms, e.g., 25% and 150% larger than O and Os, respectively, in KOs2O6, and (3) motions of the alkali metals are weakly correlated to the dynamics in their immediate environment, e.g. K in KOs2O6 is 6 times less sensitive to its local environment than Os, indicating weak bonding of the K. There is broadening of the elemental spectra of the alkali metals from Cs to K corresponding to a similar broadening of the local potential around these atoms as determined from potential of mean-force calculations. This feature of the spectra is partly explained by the well-known increase in the relative cage volume with decreasing atomic size of the alkali metal. We find that for the smallest rattler in this series (K) the larger relative cage volume allows this atom freedom to explore a large space inside the cage leading to vibration at a broader range of frequencies, hence a broader spectrum. Thus, since K is considered the best rattler in this series, these findings suggest that a significant feature of a good rattler is the ability to vibrate at several different but closely spaced frequencies.
Publisher: Elsevier BV
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 26-07-2016
DOI: 10.1038/SREP30530
Abstract: Phonons in condensed matter materials transmit energy through atomic lattices as coherent vibrational waves. Like electronic and photonic properties, an improved understanding of phononic properties is essential for the development of functional materials, including thermoelectric materials. Recently, an Einstein rattling mode was found in thermoelectric material Na 0.8 CoO 2 , due to the large displacement of Na between the [CoO 2 ] layers. In this work, we have realized a different type of rattler in another thermoelectric material Ca 3 Co 4 O 9 by chemical doping, which possesses the same [CoO 2 ] layer as Na 0.8 CoO 2 . It remarkably suppressed the thermal conductivity while enhancing its electrical conductivity. This new type of rattler was investigated by inelastic neutron scattering experiments in conjunction with ab-initio molecular dynamics simulations. We found that the large mass of dopant rather than the large displacement is responsible for such rattling in present study, which is fundamentally different from skutterudites, clathrates as well as Na analogue. We have also tentatively studied the phonon band structure of this material by DFT lattice dynamics simulation, showing the relative contribution to phonons in the distinct layers of Ca 3 Co 4 O 9.
Publisher: Elsevier BV
Date: 09-2021
Publisher: IOP Publishing
Date: 04-07-2014
DOI: 10.1088/0953-8984/26/30/305401
Abstract: Rattling dynamics have been identified as fundamental to superconductivity in defect pyrochlore osmates and aluminium vanadium intermetallics, as well as low thermal conductivity in clathrates and filled skutterudites. Combining inelastic neutron scattering (INS) measurements and ab initio molecular dynamics (MD) simulations, we use a new approach to investigate rattling in the Al-doped defect pyrochlore tungstates: AAl0.33W1.67O6 (A = K, Rb, Cs). We find that although all the alkali metals rattle, the rattling of the K atoms is unique, not only among the tungstates but also among the analogous defect osmates, KOs2O6 and RbOs2O6. Detailed analysis of the MD trajectories reveals that two unique features set the K dynamics apart from the rest, namely, (1) quasi one-dimensional local diffusion within a cage, and (2) vibration at a range of frequencies. The local diffusion is driven by strongly anharmonic local potentials around the K atoms exhibiting a double-well structure in the direction of maximum displacement, which is also the direction of local diffusion. On the other hand, vibration at a range of frequencies is a consequence of the strong anisotropy in the local potentials around the K atoms as revealed by directional magnitude spectra. We present evidence to show that it is the smaller size rather than the smaller mass of the K rattler which leads to the unusual dynamics. Finally, we suggest that the occurrence of local diffusion and vibration at a range of frequencies in the dynamics of a single rattler, as found here for the K atoms, may open new possibilities for phonon engineering in thermoelectric materials.
Publisher: IOP Publishing
Date: 21-05-2010
DOI: 10.1088/0953-8984/22/22/223201
Abstract: Understanding the electronic charge distribution around oxygen vacancies in transition metal and rare earth oxides is a scientific challenge of considerable technological importance. We show how significant information about the charge distribution around vacancies in cerium oxide can be gained from a study of high resolution crystal structures of higher order oxides which exhibit ordering of oxygen vacancies. Specifically, we consider the implications of a bond valence sum analysis of Ce₇O₁₂ and Ce₁₁O₂₀. To illuminate our analysis we show alternative representations of the crystal structures in terms of orderly arrays of coordination defects and in terms of fluorite-type modules. We found that in Ce₇O₁₂, the excess charge resulting from removal of an oxygen atom delocalizes among all three triclinic Ce sites closest to the O vacancy. In Ce₁₁O₂₀, the charge localizes on the next nearest neighbour Ce atoms. Our main result is that the charge prefers to distribute itself so that it is farthest away from the O vacancies. This contradicts the standard picture of charge localization which assumes that each of the two excess electrons localizes on one of the cerium ions nearest to the vacancy. This standard picture is assumed in most calculations based on density functional theory (DFT). Based on the known crystal structure of Pr₆O₁₁, we also predict that the charge in Ce₆O₁₁ will be found in the second coordination shell of the O vacancy. We also extend the analysis to the Magnéli phases of titanium and vanadium oxides (M(n)O(₂n₋₁), where M = Ti, V) and consider the problem of metal-insulator transitions (MIT) in these oxides. We found that the bond valence analysis may provide a useful predictive tool in structures where the MIT is accompanied by significant changes in the metal-oxygen bond lengths. Although this review focuses mainly on bulk cerium oxides with some extension to the Magnéli phases of titanium and vanadium, our approach to characterizing electronic properties of oxygen vacancies and the physical insights gained should also be relevant to surface defects and to other rare earth and transition metal oxides.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0FD00034E
Abstract: We use ab initio molecular dynamics simulations to obtain classically the effects of H2O cage motions on the potential-energy surface (PES) of encapsulated H2 in the H2/tetrahydrofuran-hydrate system. The significant differences between the PES for the H2 in rigid and flexible cages that we find will influence calculation of the quantum dynamics of the H2. Part of these differences arises from the relaxation of the H2O cage around the classical H2, with a second part arising from the coupling of both translational and rotational motions of H2 with the H20 cage. We find that isotopic substitution of 2H for 1H of the H2O cage affects the coupling, which has implications for experiments that require the use of 2H2O, including inelastic neutron scattering that uses 2H2O cages in order to focus on the H2 guest dynamics. Overall, this work emphasizes the importance of taking into account cage dynamics in any approach used to understand the dynamics of H2 guests in porous framework materials.
Publisher: IOP Publishing
Date: 07-2020
Abstract: Li-ion batteries have revolutionized the portable electronics industry and empowered the electric vehicle (EV) revolution. Unfortunately, traditional Li-ion chemistry is approaching its physicochemical limit. The demand for higher density (longer range), high power (fast charging), and safer EVs has recently created a resurgence of interest in solid state batteries (SSB). Historically, research has focused on improving the ionic conductivity of solid electrolytes, yet ceramic solids now deliver sufficient ionic conductivity. The barriers lie within the interfaces between the electrolyte and the two electrodes, in the mechanical properties throughout the device, and in processing scalability. In 2017 the Faraday Institution, the UK’s independent institute for electrochemical energy storage research, launched the SOLBAT (solid-state lithium metal anode battery) project, aimed at understanding the fundamental science underpinning the problems of SSBs, and recognising that the paucity of such understanding is the major barrier to progress. The purpose of this Roadmap is to present an overview of the fundamental challenges impeding the development of SSBs, the advances in science and technology necessary to understand the underlying science, and the multidisciplinary approach being taken by SOLBAT researchers in facing these challenges. It is our hope that this Roadmap will guide academia, industry, and funding agencies towards the further development of these batteries in the future.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CP05818K
Abstract: The dependence of the electronic and thermoelectric properties of the ternary chalcogenides Cu(Sb,Bi)(S,Se) 2 on hydrostatic pressure is determined.
Publisher: Elsevier BV
Date: 2021
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: Saudi Arabia
Location: Australia
No related grants have been discovered for Elvis Shoko.