Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L12: Focus Session: Oxide and Chalcogenide Thermoelectric Materials |
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Sponsoring Units: DMP GERA FIAP DCOMP Chair: Zhifeng Ren, University of Houston Room: 007C |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L12.00001: Theoretical survey of doped sodium cobaltate and strategies for enhancing the thermoelectric performance M. Hussein N. Assadi, Hiroshi Katayama-Yoshida Doped $Na_xCoO_2$ is suitable for highly efficient thermoelectric conversion at $\approx$ 1000 K. However, due to complex lattice structure and strong correlation effects, atomistic understanding of dopant's influence is challenging to resolve experimentally. We examined a wide range of dopants' electronic structures using density functional method. We found that dopants like Mg, Ba, Sr, Au and Eu always substitute Na for all Na concentrations. In contrast, dopants like Ni, Bi, W, Sb and Sn always substitute Co regardless of Na concentration. Furthermore, there is a third class of dopants like Cu and Y that substitute Na for $x\leq0.5$, but for higher Na concentrations, they substitute Co. In the case of $Mg_{Na}$, we could experimentally verify Mg's local chemical environment using Raman spectroscopy therefore validating the theoretical results. The implication of Na-substituting dopants on thermoelectric performance is the immobilization of Na ions which behave similar to ionic liquid in pristine $Na_xCoO_2$. This immobilization reduces the resistivity by improving the mobility of carriers and thus enhancing the thermo-power. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L12.00002: Anisotropic transport in single-crystal molybdenum bronze, Li$_{0.33}$MoO$_{3}$ Saeed Moshfeghyeganeh, Joshua L. Cohn, John J. Neumeier We present transport measurements (resistivity, thermopower, thermal conductivity) on single crystals of the quasi-one-dimensional semiconductor Li$_{0.33}$MoO$_{3}$ in the temperature range 200-500 K. First synthesized and studied long ago,\footnote{B. T. Collins {\it et al.}, J. Sol. St. Chem. {\ bf 76}, 319 (1988).} the thermal and thermoelectric properties for this compound have not been previously reported. We find extreme anisotropy in the Seebeck coefficient within the $a-c$ planes, with $S_c-S_a\simeq 300 \mu$V/K near room temperature. The thermal conductivity at room temperature in the $a-c$ planes was $\sim 1.5-2$~W/mK and 7-8 times smaller along $b^*$. We also report x-ray studies of the out-of-plane ($b^*$) lattice constants indicating a small structural transition at $T\approx 350$~K that coincides with anomalies in the transport properties. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L12.00003: Thermoelectric properties of amorphous ZnO-based materials using {\em ab initio} methods Anindya Roy, Yu-Ting Cheng, Michael L. Falk We use a combination of computational methods - molecular dynamics and density functional theory, to predict thermoelectric properties of amorphous ZnO-based materials. We use BoltzTraP [1] to calculate properties such as Seebeck coefficient and electrical conductivity within semiclassical Boltzman transport theory, and compare with available experimental results. Additionally, we investigate the change in the thermoelectric parameters caused by alloying amorphous ZnO with tin and other elements. Our preliminary calculations suggest that the thermoelectric performance of amorphous ZnO is on par with the crystalline counterpart. This is encouraging - since amorphous materials are yet to be studied in depth for their potential as thermoelectric materials, and they could see much improvement with sustained effort. Also, while {\it ab initio} methods are routinely used to predict properties of crystalline systems, their application in amorphous systems is a less-explored area. \\[4pt] [1] BoltzTraP: Madsen, G. K. and Singh, D. J., Comput. Phys. Commun. {\bf 175}, 67-71 (2006). [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 9:12AM |
L12.00004: Perovskite- and Heusler based materials for thermoelectric converters Invited Speaker: Anke Weidenkaff The broad application of thermoelectric converters in future energy technologies requires the development of active, stable, low cost and sustainable materials. Semiconductors based on perovskite and heusler structures show substantial potential for thermoelectric energy conversion processes [1-3]. Their good performance can be explained based on their suitable band structure, adjusted charge carrier density, mass and mobility, limited phonon transport, electron filtering possibilities, strongly correlated electronic systems, etc. These properties are widely tuneable by following theoretical concepts and a deep composition-structure-property understanding to change the composition, structure and size of the crystallites in innovative scalable synthesis procedures. Improved thermoelectric materials are developed, synthesised and tested in diverse high temperature applications to improve the efficiency and energy density of the thermoelectric conversion process. The lecture will provide a summary on the field of advanced perovskite-type ceramics and Heusler compounds gaining importance for a large number of future energy technologies.\\[4pt] [1] Wenjie. J. Xie, Anke Weidenkaff, X. F. Tang, Q. J. Zhang, S. J. Poon, and Terry M. Tritt, Recent advances in nanostructured thermoelectric half-Heusler compounds, review, Nanomaterials (2012) 379-412.\\[0pt] [2] Leyre Sagarna, Sascha Populoh, Andrey Shkabko, James Eilertsen, Alexandra E. Maegli, Roland Hauert, Matthias Schrade, Lassi Karvonen, Anke Weidenkaff, Influence of the Oxygen Content on the Electronic Transport Properties of SrxEu1-xTiO3, J. Phys. Chem. C, 118 (15), (2014) 7821--7831.\\[0pt] [3] Krzysztof Galazka, Sascha Populoh, Leyre Sagarna, Lassi Karvonen, Wenjie Xie1, Alessandra Beni, Patrik Schmutz, J\"{u}rg Hulliger and Anke Weidenkaff, Phase formation, stability and oxidation in the (Ti,Zr,Hf)NiSn half-Heusler system, Phys. Status Solidi A 211, No. 6, (2014)1259--1266. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L12.00005: Thermoelectric properties of Cl-doped In$_{4}$Pb$_{0.01}$Sn$_{0.03}$Se$_{2.9}$Cl$_{x}$ polycrystalline compounds Jin-hee Kim, Min Jae Kim, Suekyung Oh, Jong-Soo Rhyee, Su-Dong Park We investigated thermoelectric properties of Cl-doped polycrystalline compounds of In$_{4}$Pb$_{0.01}$Sn$_{0.03}$Se$_{2.9}$Cl$_{x}$ (x $=$ 0.02, 0.04 and 0.06). The x-ray diffraction measurement shows gradual change of lattice volume for x $\le $ 0.04 without any impurity phases indicating systemic change of Cl-doping. The Cl-doping in the compounds has an effect of increasing carrier concentration and effective mass of carrier resulting in the increase of power factor near 700 K than In$_{4}$Pb$_{0.01}$Sn$_{0.03}$Se$_{2.9}$. Because of the increased electrical conductivity neat 700 K, the thermoelectric figure-of-merit ZT is 1.25 at 723 K for x $=$ 0.04 Cl-doped compound which is relatively high value as n-type polycrystalline materials. [Preview Abstract] |
(Author Not Attending)
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L12.00006: Effects of Ge replacement in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration modified by local electron imbalance E.M. Levin, A. Howard, W.E. Straszheim XRD, SEM, EDS, $^{125}$Te NMR, Seebeck coefficient, and electrical resistivity of Ag$_{x}$Ge$_{50-x}$Te$_{50}$ and Sb$_{x}$Ge$_{50-x}$Te$_{50}$ alloys have been studied. Replacement of Ge in GeTe by Sb significantly increases the Seebeck coefficient, while replacement by Ag decreases it. These effects can be attributed to a change in carrier concentration observed via $^{125}$Te NMR spin-lattice relaxation measurements and NMR signal position, which mostly depends on the Knight shift. Variation in carrier concentration in Ag$_{x}$Ge$_{50-x}$Te$_{50}$ and Sb$_{x}$Ge$_{50-x}$Te$_{50}$ can be attributed to different electron configurations of valence electrons of Ag (4$d^{10}$5$s^{1})$ and Sb (5$s^{2}$5$p^{3})$ compared to that of Ge (4$s^{2}$4$p^{2})$ resulting in local electron imbalances and changing the concentration of charge carrier (holes) generated by Ge vacancies. In contrast, our $^{125}$Te NMR and Seebeck coefficient data for Ag$_{2}$Sb$_{2}$Ge$_{46}$Te$_{50}$ are similar to those observed for GeTe. This shows that effects from Ag and Sb compensate each other and indicates the existence of [Ag$+$Sb] pairs. The effects of Ge replacement in GeTe by Ag, Sb, or [Ag$+$Sb] on rhombohedral lattice distortion also have been analyzed. Interplay between the Seebeck coefficient and electrical resistivity in these alloys results in variation of power factor; the value of 45 mW/cm K$^{2}$, the highest among known tellurides, was found for Sb$_{2}$Ge$_{48}$Te$_{50}$. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L12.00007: Raman Spectroscopy of the Thermoelectric Sr$_{0.61}$Ba$_{0.39}$Nb$_{2}$O$_{6}$ Michael Primrose, Jean Toulouse, Jonathan Bock, Clive Randall Strontium Barium Niobate (SBN) has recently been shown by Lee et al. [1] to exhibit high thermoelectric power factors at temperatures above 500 K when it has been highly reduced. To determine the effects of reduction on the phonons, the Raman spectra of \textit{unreduced} and \textit{reduced} SBN have been measured at room temperature along the axis of polarization (\textbf{\textit{c}}-axis) and perpendicular to it (\textbf{\textit{a}}-axis). The Raman features of the \textit{unreduced} crystal are found to be very broad and overlapping. In particular, a strong Lorentzian central (quasi-elastic) peak extending out to 400cm$^{-1}$ is observed for light polarized along the \textbf{\textit{a}} axis. By contrast and unexpectedly in the \textit{reduced} crystal, thought to be more disordered, well resolved Raman peaks are observed, particularly at low frequencies. Also in the \textit{reduced} crystal, the central peak is much suppressed and narrower, but a new peak appears at 1000cm$^{-1}$ for both \textbf{\textit{c}} and \textbf{\textit{a}} polarizations. In addition, the high frequency peaks (\textgreater 200 cm$^{-1})$ appear to broaden and to shift toward higher frequencies. High temperatures results may be available at the time of the conference. \\[4pt] [1] S. Lee, J.A. Block, S. Trolier-McKinstry and C. Randall, J. Europ. Ceram. Soc. v.32, p.3971 (2012) [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:24AM |
L12.00008: Bulk oxides: asymmetry between p-and n-type transport properties Invited Speaker: Antoine Maignan The thermoelectric power (TEP) of transition metal oxides shows large difference depending on the sign of the charge carriers. In electron-doped oxides, the best TEs in terms of the figure of merit are heavily doped transparent conductors (as doped ZnO). The physics is very similar to that of semiconductors, though the defects chemistry differs: the existence of planar defects created by the doping elements, is far from the random distribution in semiconductors. In contrast the best p-types are layered cobaltites (CdI$_{2}$ -type layers with edge-shared CoO$_{6}$ octahedras). The Co cations adopt a low spin state. Both electronic correlations and spin entropy have to be considered to explain the S(T) curve for T \textless 150K, whereas for T\textgreater 150K, the spin/orbital configurations and the doping level in the generalized Heikes formula are dominating. This description supported by the results obtained for perovskite ruthenates was recently unvalidated for the quadruple perovskite ACu$_{3}$Ru$_{4}$O$_{12}$, showing very different S(T) without S saturation up to $\sim $ 900K. Their Pauli paramagnetism enlights the role of the spins upon thermopower. Similarly, searching for other n-types, interesting TE properties have been found in Ba$_{1.2}$Mn$_{8}$O$_{16}$: the S(T) evidences a charge/orbital ordering in this manganite (v$_{\mathrm{Mn}}$ $=$ 3.7) coupled to an abrupt change in the unit-cell volume. Ba$_{1.2}$Mn$_{8}$O$_{16}$, although of n-type, exhibits a cst. $|S| \approx $92$\mu $V.K$^{-1}$ for T\textgreater 400K, explained by the generalized Heikes formula rather used for p-type. This difference with other n-type oxides is related to the Mn$^{3+}$/Mn$^{4+}$ magnetism and the contribution of e$_{\mathrm{g}}$ orbitals for the transport properties. In this presentation, the richness of the TE properties of metal transition oxides will be emphasized focusing on the important role of the spins. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L12.00009: Enhancement of Thermoelectric Performance in n-type PbTe$_{1-y}$Se$_{y}$ by Cr Doping Eyob Chere, Qian Zhang, Kenneth McEnaney, Mengliang Yao, Feng Cao, Cyril Opeil, Gang Chen, Zhifeng Ren Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications. However, little emphasis has been given to improve the figure-of-merit (\textit{ZT}) near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe$_{1-y}$Se$_{y}$ with $y =$ 0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak \textit{ZT} temperature increased with increasing concentration of Se. A highest \textit{ZT} of $\sim$ 0.6 at room temperature in Te-rich Cr$_{0.015}$Pb$_{0.985}$Te$_{0.75}$Se$_{0.25}$ was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about -220 $\mu$V K$^{-1\, }$and high Hall mobility $\sim$ 1120 cm$^{2}$ V$^{-1\, }$s$^{-1}$ at room temperature. A room temperature \textit{ZT} of $\sim$ 0.5 and peak \textit{ZT} of $\sim$ 1 at about 573 K to 673 K is shown by Se-rich sample Cr$_{0.01}$Pb$_{0.99}$Te$_{0.25}$Se$_{0.75}$. This improvement of the room temperature \textit{ZT} improved the average \textit{ZT} over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Te-rich Cr$_{0.015}$Pb$_{0.985}$Te$_{0.75}$Se$_{0.25}$ up to $\sim$ 11 {\%} and Se-rich Cr$_{0.01}$Pb$_{0.99}$Te$_{0.25}$Se$_{0.75}$ up to $\sim$ 13 {\%} with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L12.00010: Phonon Dispersions of Thermoelectric SnSe Chen Li, Jiawang Hong, Andrew May, Jie Ma, Tao Hong, Songxue Chi, Georg Ehlers, Olivier Delaire SnSe has recently attracted significant interest as a thermoelectric material with very high $zT>2$ along two crystallographic axes. A favorable property of SnSe is its very low thermal conductivity, which is below $1Wm^{-1}K^{-1}$ along all axes even at ambient temperature, and decreases with temperature. However, the degree of anisotropy of the thermal conductivity remains somewhat controversial. We present our results of detailed inelastic neutron scattering measurements of the phonon dispersions and their temperature dependence. The results are compared with first-principles calculations to investigate the origin of the low thermal conductivity and its anisotropy. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L12.00011: Ultrafast investigation of photo-excited carrier-lattice dynamics in PbTe using Fourier-transform inelastic X-ray scattering Mason Jiang, Crystal Bray, Jesse Clark, Tom Henighan, Mike Kozina, Aaron Lindenberg, Mariano Trigo, Peter Zalden, David Reis, Matthieu Chollet, James Glownia, Matthias Hoffmann, Diling Zhu, Olivier Delaire, Andrew May, Brian Sales, Stephen Fahy, Eamonn Murray, Ivana Savic We report with fine temporal and momentum resolution non-equilibrium electron-phonon and phonon-phonon dynamics in the widely-used thermoelectric material PbTe. The measurements are made possible by both the intense, ultrafast X-ray pulses of the Linac Coherent Light Source instrument and the recently developed Fourier-transform inelastic X-ray scattering (FT-IXS) technique. We demonstrate experimentally the various effects of impulsive optical photo-excitation on the lattice dynamics of the material as carriers are dramatically redistributed in the system. Specifically, coupled two-phonon states are excited throughout various Brillouin zones and possible plasmon-phonon modes are observed very near zone center. Coupled with calculations from density functional theory (DFT), an analysis of these photo-excited modes yields new insight into the origins of the incipient ferroelectricity and zone center anomalies noted in past measurements on PbTe. [Preview Abstract] |
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