ORCID Profile
0000-0003-1414-8682
Current Organisation
Northwestern University
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Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4TA00072B
Abstract: Solid solutions of GeTe, AgInTe 2 and optionally AgSbTe 2 (accessible via high-pressure synthesis or by quenching, depending on the phases’ In content) exhibit remarkable thermoelectric properties that clearly reflect transitions between metastable and stable phases.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TA01667C
Abstract: Highly dense Cu 2−x S bulks, fabricated by a melt-solidification technique, show high thermoelectric performance with zT of ∼1.9 at 970 K.
Publisher: Wiley
Date: 05-02-2015
Publisher: American Physical Society (APS)
Date: 24-07-2015
Publisher: Wiley
Date: 14-08-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3CE41815D
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: 20-02-2008
Publisher: American Chemical Society (ACS)
Date: 11-04-2016
Abstract: Driven by the prospective applications of thermoelectric materials, massive efforts have been dedicated to enhancing the conversion efficiency. The latter is governed by the figure of merit (ZT), which is proportional to the power factor (S(2)σ) and inversely proportional to the thermal conductivity (κ). Here, we demonstrate the synthesis of high-quality ternary Bi2Te3-xSex nanoplates using a microwave-assisted surfactant-free solvothermal method. The obtained n-type Bi2Te2.7Se0.3 nanostructures exhibit a high ZT of 1.23 at 480 K measured from the corresponding sintered pellets, in which a remarkably low κ and a shift of peak S(2)σ to high temperature are observed. By detailed electron microscopy investigations, coupled with theoretical analysis on phonon transports, we propose that the achieved κ reduction is attributed to the strong wide-frequency phonon scatterings. The shifting of peak S(2)σ to high temperature is due to the weakened temperature dependent transport properties governed by the synergistic carrier scatterings and the suppressed bipolar effects by enlarging the band gap.
Publisher: American Chemical Society (ACS)
Date: 07-07-2014
DOI: 10.1021/IC5010243
Abstract: Te/Sb/Ge/Ag (TAGS) materials with rather high concentrations of cation vacancies exhibit improved thermoelectric properties as compared to corresponding conventional TAGS (with constant Ag/Sb ratio of 1) due to a significant reduction of the lattice thermal conductivity. There are different vacancy ordering possibilities depending on the vacancy concentration and the history of heat treatment of the s les. In contrast to the average α-GeTe-type structure of TAGS materials with cation vacancy concentrations <∼3%, quenched compounds like Ge0.53Ag0.13Sb0.27□0.07Te1 and Ge0.61Ag0.11Sb0.22□0.06Te1 exhibit "parquet-like" multidomain nanostructures with finite intersecting vacancy layers. These are perpendicular to the pseudocubic directions but not equidistantly spaced, comparable to the nanostructures of compounds (GeTe)nSb2Te3. Upon heating, the nanostructures transform into long-periodically ordered trigonal phases with parallel van der Waals gaps. These phases are slightly affected by stacking disorder but distinctly different from the α-GeTe-type structure reported for conventional TAGS materials. Deviations from this structure type are evident only from HRTEM images along certain directions or very weak intensities in diffraction patterns. At temperatures above ∼400 °C, a rock-salt-type high-temperature phase with statistically disordered cation vacancies is formed. Upon cooling, the long-periodically trigonal phases are reformed at the same temperature. Quenched nanostructured Ge0.53Ag0.13Sb0.27□0.07Te1 and Ge0.61Ag0.11Sb0.22□0.06Te1 exhibit ZT values as high as 1.3 and 0.8, respectively, at 160 °C, which is far below the phase transition temperatures. After heat treatment, i.e., without pronounced nanostructure and when only reversible phase transitions occur, the ZT values of Ge0.53Ag0.13Sb0.27□0.07Te1 and Ge0.61Ag0.11Sb0.22□0.06Te1 with extended van der Waals gaps amount to 1.6 at 360 °C and 1.4 at 410 °C, respectively, which is at the top end of the range of high-performance TAGS materials.
Publisher: Elsevier BV
Date: 12-2017
Publisher: American Chemical Society (ACS)
Date: 24-07-2017
Publisher: Elsevier BV
Date: 11-2014
Publisher: IEEE
Date: 08-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TA05455J
Abstract: We demonstrate that insulating-boron nanoparticle inclusion in Cu 2 Se has little effect on the overall power factor, but can significantly reduce the thermal conductivity, resulting in great improvement on zT , by a factor of 1.6–2.6 compared to undoped Cu 2 Se over a wide range of temperatures.
Publisher: Wiley
Date: 06-05-2021
Abstract: The poor carrier mobility of polycrystalline Mg 3 Sb 2 at low temperatures strongly degrades the thermoelectric performance. Ionized impurities are initially thought to dominate charge carrier scattering at low temperatures. Accordingly, the increased electrical conductivity by replacing Mg with metals such as Nb is also attributed to reduced ionized impurity scattering. Recent experimental and theoretical studies challenge this view and favor the grain boundary (GB) scattering mechanism. A reduction of GB scattering improves the low‐temperature performance of Mg 3 (Sb, Bi) 2 alloys. However, it is still elusive how these metal additions reduce the GB resistivity. In this study, Nb‐free and Nb‐added Mg 3 Sb 2 are studied through diffraction, X‐ray absorption spectroscopy, solid‐state nuclear magnetic resonance spectroscopy, and atom probe tomography. It is shown that Nb does not enter the Mg 3 Sb 2 matrix and remains in the metallic state. Besides, Nb diffuses along the GB forming a wetting layer, which modifies the interfacial energy and accelerates grain growth. The GB resistivity appears to be reduced by Nb‐enrichment, as evidenced by modeling the electrical transport properties. This study not only confirms the GB scattering in Mg 3 Sb 2 but also reveals the hitherto hidden role of metallic additives on enhancing grain growth and reducing the GB resistivity.
Publisher: IOP Publishing
Date: 11-01-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7TA02677C
Abstract: Owing to the convergence of multivalence bands, the thermoelectric performance of polycrystalline SnSe was significantly enhanced.
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: Springer Science and Business Media LLC
Date: 14-03-2014
Publisher: American Chemical Society (ACS)
Date: 07-06-2013
DOI: 10.1021/JP4041666
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3CP54493A
Abstract: Recently a significant improvement in the thermoelectric performance of p-type ternary PbTe-PbSe and PbTe-PbS systems has been realized through alternating the electronic band structure and introducing nano-scale precipitates to bulk materials respectively. However, the quaternary system of PbTe-PbSe-PbS has received less attention. In the current work, we have excluded phase complexity by fabricating single phase sodium doped PbTe, alloyed with PbS up to its solubility limit which is extended to larger concentrations than in the ternary system of PbTe-PbS due to the presence of PbSe. We have presented a thermoelectric efficiency of approximately 1.6 which is superior to ternary PbTe-PbSe and PbTe-PbS at similar carrier concentrations and the binary PbTe, PbSe and PbS alloys. The quaternary system shows a larger Seebeck coefficient than the ternary PbTe-PbSe alloy, indicative of a wider band gap, valence band energy offset and heavier carriers effective mass. In addition, the existence of PbS in the alloy further reduces the lattice thermal conductivity originated from phonon scattering on solute atoms with high contrast atomic mass. Single phase quaternary PbTe-PbSe-PbS alloys are promising thermoelectric materials that provide high performance through adjusting the electronic band structure by regulating chemical composition.
Publisher: Elsevier BV
Date: 09-2021
Publisher: Elsevier BV
Date: 10-2010
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: 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: Wiley
Date: 19-07-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0EE00491J
Abstract: Addressing the irregular electrical conductivity in PbQ–NaSbQ 2 thermoelectrics. Increasing the NaSbSe 2 fraction weakens charge carrier screening and strengthens GB scattering.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3TA11654A
Publisher: Wiley
Date: 07-2019
Publisher: American Chemical Society (ACS)
Date: 07-08-2020
DOI: 10.1021/JACS.0C07067
Publisher: Elsevier BV
Date: 2020
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: Springer Science and Business Media LLC
Date: 27-06-2004
DOI: 10.1038/NMAT1154
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TC01509J
Abstract: The precipitation of skutterudite-type crystallites in germanium antimony tellurides yields intriguing materials with respect to their thermoelectric performance, especially due to a very low phononic part of the lattice thermal conductivity.
Publisher: Elsevier BV
Date: 11-2017
Publisher: AIP Publishing
Date: 27-02-2015
DOI: 10.1063/1.4913992
Abstract: The electrical resistivity curves for binary phase compounds of p-type lead chalcogenide (PbTe)(0.9−x)(PbSe)0.1(PbS)x, (x = 0.15, 0.2, 0.25), which contain PbS-rich secondary phases, show different behaviour on heating and cooling between 500-700 K. This is contrast to single phase compounds which exhibit similar behaviour on heating and cooling. We correlate these anomalies in the electrical resistivities of multiphase compounds to the variation in phase composition at high temperatures. The inhomogeneous distribution of dopants between the matrix and secondary phase is found to be crucial in the electronic transport properties of the multiphase compounds. These results can lead to further advances in designing composite Pb-chalcogenides with high thermoelectric performance.
Location: United States of America
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