Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T12: Focus Session: Thermoelectrics Materials I |
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Sponsoring Units: DMP GERA FIAP Chair: Michael McGuire, ORNL Room: 314 |
Thursday, March 21, 2013 8:00AM - 8:36AM |
T12.00001: Emergent nanoscale fluctuations in high rock-salt PbTe Invited Speaker: Simon Billinge Lead Telluride is one of the most promising thermoelectric materials in the temperature range just above room temperature. It is a narrow band gap semiconductor with a high Seebeck coefficient and a low thermal conductivity. It is structurally much simpler than many other leading candidates for high performance thermoelectrics being a binary rock-salt, isostructural to NaCl. The thermoelectric figure of merit, ZT, can be markedly improved by alloying with various other elements by forming quenched nanostructures. The undoped endmember, PbTe, does not have any such quenched nanostructure, yet has a rather low intrinsic thermal conductivity. There are also a number of interesting and non-canonical behaviors that it exhibits, such as an increasing measured band-gap with increasing temperature, exactly opposite to what is normally seen due to Fermi smearing of the band edge, and an unexpected non-monotonicity of the band gap in the series PbTe - PbSe - PbS. The material is on the surface simple, but hides some interesting complexity. We have investigated in detail the PbTe endmember using x-ray and neutron diffraction and neutron inelastic scattering [1]. To our surprise, using the atomic pair distribution function (PDF) analysis of neutron powder diffraction data we found that an interesting and non-trivial local structure that appears on warming. with the Pb atoms moving off the high-symmetry rock-salt positions towards neighboring Te ions. No evidence for the off-centering of the Pb atoms is seen at low temperature. The crossover from the locally undistorted to the locally distorted state occurs on warming between 100~K and 250~K. This unexpected emergence of local symmetry broken distortions from an undistorted ground-state we have called emphanisis, from the Greek for appearing from nothing. We have also investigated the lattice dynamics of the system to search for a dynamical signature of this behavior and extended the studies to doped systems and I will also describe the results of these experiments. This work gives key insights into PbTe, the possible origin of its anomalous electronic structure properties, and why it is such an attractive parent compound for nanostructured high performance thermoelectric materials. I would like to acknowledge the excellent collaborations that occurred during this work, including Emil Bozin at Brookhaven National Laboratory, Mercouri Kanatzidis and Christos Malliakas at Northwestern University and Argonne National Laboratory, Kirsten Jensen from U. Aarhus, Steve Shapiro at Brookhaven National Laboratory, Matt Stone and Mark Lumsden at Oak Ridge National Laboratory, Nicola Spalding at ETH Zurich and Petros Souvatzis at Los Alamos National Laboratory. I would also like to acknowledge the support of the national user facilities and their staff where the work was done. [1] E.S. Bozin et al., Science v330, pp1660 (2010). [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 8:48AM |
T12.00002: Thermoelectric properties of FeSb2: A first principles study Momar Diakhate, Matthieu Verstraete The development of new types of thermoelectric materials with a large figure of merit is strongly driven by the need for sustainable and clean energy. In this respect first-principles study of thermoelectric properties can help to achieve a better understanding of microscopic mechanisms in transport, which provides insight for discovering new materials. To study the thermoelectrical properties, we combine the well known Boltzmann transport theory with the predictive power of density functional calculations. With the exception of the lattice thermal conductivity, all of the required transport coefficients can be obtained using the BoltzTrap code, based simply on the electronic band energies. With a constant relaxation time, we predict the Seebeck coefficient of bulk FeSb2, which showed colossal negative value at 12K experimentally. The calculated peak position is consistent with the observation, while the amplitude is underestimated. The inclusion of contributions from phonon drag effect and the exact calculation of the electronic density of states around Fermi level may better describe the experimentally observed phenomena. [Preview Abstract] |
Thursday, March 21, 2013 8:48AM - 9:00AM |
T12.00003: Large Seebeck Effect in CrSb$_{2}$ Single Crystals Brian Sales, Andrew May, Michael McGuire, David Singh, David Mandrus CrSb$_{2}$ is a narrow gap semiconductor (E$_{\mathrm{g}} =$ 0.14 meV) that orders antiferromagnetically at T$_{\mathrm{N}} =$ 273 K. Resistivity, Hall effect, Seebeck coefficient, thermal conductivity, heat capacity, and magnetic susceptibility data are reported for CrSb$_{2}$ single crystals. In spite of some unusual features in electrical transport and Hall measurements below 100 K, only one phase transition occurs (T$_{\mathrm{N}})$ in the temperature range from 2 to 750 K. Many of the low temperature properties can be explained by the thermal depopulation of carriers from the conduction band into a low mobility impurity band about 16 meV below the conduction band edge. The Seebeck coefficient, S, is large and negative from 2 to 300 K, ranging from -70 $\mu $V/K at 300 K to -4500 $\mu $V/K at 18 K. The large magnitude of S at 18 K is likely due to phonon drag, with the large decrease in the magnitude of S below 18 K due to the thermal depopulation of the high mobility conduction band. The CrSb$_{2}$ Seebeck data are compared to some of the data reported for FeSb$_{2}$ and FeSi. This research was supported by the U. S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. [Preview Abstract] |
Thursday, March 21, 2013 9:00AM - 9:12AM |
T12.00004: Magnon gap formation and charge density wave effect on thermoelectric properties in SmNiC2 compound Jin-hee Kim, Jong-Soo Rhyee, Yong Seung Kwon We studied the magnetic, electrical, and thermal properties of polycrystalline compound of SmNiC2. The electrical resistivity and magnetization measurement show the interplay between the charge density wave at T$_{\mathrm{CDW}} =$ 157 K and the ferromagnetic ordering of Tc $=$ 18 K. Below the ferromagnetic transition temperature, we observed the magnon gap formation of 4.3 $\sim$ 4.4 meV by $\rho $(T) and C$_{\mathrm{p}}$(T) measurements. The charge density wave is attributed to the increase of Seebeck coefficient resulting in the increase of power factor S$^{\mathrm{2}}\sigma $. The thermoelectric figure-of-merit ZT significantly increases due to the increase of power factor at T$_{\mathrm{CDW}} =$ 157 K. Here we argue that the competing interaction between electron-phonon and electron-magnon couplings exhibits the unconventional behavior of electrical and thermal properties. This research was supported by Basic Science Research Program (2011-0021335), Nano-Material Technology Development Program (2011-0030147), and Mid-career Research Program (Strategy) (No. 2012R1A2A1A03005174) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology. [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:24AM |
T12.00005: New insights into rare-earth intermetallic alloys for cryogenic Peltier cooling Stephen Boona, Donald Morelli Strongly correlated materials such as intermediate valence CePd$_{3}$ have long been considered attractive candidates for cryogenic Peltier cooling due to the combination of metallic electrical resistivity concurrent with Seebeck coefficient values on the order of 100 $\mu$ V/K at low temperatures. This behavior is a direct result of the strong hybridization of localized 4f states with delocalized conduction electrons, which gives rise to several unusual structural, electronic, thermal, and magnetic properties. Our recent work on this compound has helped to unravel some of the complex ways in which these properties are correlated, and we have successfully utilized this improved understanding to enhance ZT up to 0.3. We present a broad overview of these new insights and provide suggestions for how they may be exploited to achieve enhanced thermoelectric performance in other strongly correlated materials. [Preview Abstract] |
Thursday, March 21, 2013 9:24AM - 9:36AM |
T12.00006: Low Temperature Specific Heat Study on Type I Clathrates Jiazhen Wu, Jingtao Xu, Gang Mu, Dwi Prananto, Hidekazu Shimotani, Yoichi Tanabe, Satoshi Heguri, Katsumi Tanigaki Zintl phase clathrates, which are featured by the cage framework with guest atoms accommodated inside, are considered as good candidates of thermoelectric materials mainly due to the low thermal conductivity caused by large scattering of the acoustic phonons via the rattling phonons arising from the guest motions [1,2]. The fact has been known so far that, in clathrate Sr$_{\mathrm{8}}$Ga$_{\mathrm{16}}$Ge$_{\mathrm{30}}$ showing off-centered displacement of encapsulated elements, thermal conductivity is suppressed even stronger via the scattering of acoustic phonons by anharmonic rattling phonons. Consequently, further detailed understanding on the anharmonic potentials realized in clathrates is important. In this meeting, we will present our recent studies on low temperature specific heat of type I Ba$_{\mathrm{8}}$Ga$_{\mathrm{16}}$Sn$_{\mathrm{30}}$ and K$_{\mathrm{8}}$Ga$_{\mathrm{8}}$Sn$_{\mathrm{38}}$ in addition to those of Ba$_{\mathrm{8}}$Ga$_{\mathrm{16}}$Ge$_{\mathrm{30}}$ and Sr$_{\mathrm{8}}$Ga$_{\mathrm{16}}$Ge$_{\mathrm{30}}$ reported previously [2]. The discussion will mainly focus on the separation of the apparent linear temperature dependent terms of anharmonic rattling phonons from those of conduction electrons. The electron phonon interaction strength and the tunneling density of anharmonic potentials will be described on a basis of the analyses. [1] J. Tang, \textit{et al., Phys. Rev. Lett., }105, 176402 (2010). [2] J.-T. Xu,\textit{ et al., Phys. Rev. B, }82, 085206 (2010). [Preview Abstract] |
Thursday, March 21, 2013 9:36AM - 9:48AM |
T12.00007: Surface Modification induced Double Decoupling in Transport Properties of Polycrystalline Bi Jian He, Pooja Puneet, Ramakrishna Podila, Song Zhu, Malcolm Skove, Terry Tritt, Apparao Rao Nanostructured thermoelectric (TE) materials have gained major interest due to their ability to offer better control of electronic and thermal transport properties. Such nanostructures, with increased surface-to-volume ratio, lead to pronounced surface effects on various transport properties. In this study, we used the spark plasma sintering (SPS) process as a densification and surface modification technique for nano-structured Bi. Several samples were prepared with varying the DC pulse times and durations to tailor interface/surface properties. As a result, a complete decoupling of electrical and thermal transport (\textit{double decoupling}) in nano-structured Bi was observed with enhanced (greater than six-fold) power factor. This is a very significant improvement that goes beyond partial decoupling. Details of the TE properties will be presented. [Preview Abstract] |
Thursday, March 21, 2013 9:48AM - 10:00AM |
T12.00008: The microstructure network and thermoelectric properties of bulk (Bi,Sb)2Te3 Hye Jung Kang, Wenjie Xie, Dale Hitchcock, Jian He, Xinfeng Tang, Mark Laver, Boualem Hammouda We report small-angle neutron scattering studies on the microstructure network in bulk (Bi,Sb)2Te3 synthesized by the melt-spinning (MS) and the spark-plasma-sintering (SPS) process. We find that rough interfaces of multiscale microstructures generated by the MS are responsible for the large reduction of both lattice thermal conductivity and electrical conductivity. Our study also finds that subsequent SPS forms a microstructure network of 10 nanometer thick lamellae and smooth interfaces between them. This nanoscale microstructure network with smooth interfaces increases electrical conductivity while keeping a low thermal conductivity, making it an ideal microstructure for high thermoelectric efficiency. [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T12.00009: Electronic structure of Mn and Fe impurities in Bi-Sb-Te Byungki Ryu, Kyunghan Ahn, Sang Mock Lee, Kyu Hyoung Lee Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$-based thermoelectric materials are well known room temperature thermoelectric materials. Here we present a density-functional study of the electronic structure of Mn and Fe doped p-type Bi-Sb-Te (p-BST) to investigate the effect of metal impurities on the thermoelectronic properties. Our calculations show that, for both Mn and Fe, the substitutional impurity at the Bi/Sb-site is the most stable geometry. Mn is a single acceptor, whereas Fe is an isovalent defect. The metal $d$ bands are located within the host bands, not in the band gap. Due to the octahedral symmetry of the Bi/Sb-site, the metal $d$ bands of Mn and Fe are split into three t$_{\mathrm{2g}}$ and two e$_{\mathrm{g}}^{\mathrm{\ast }}$ states in the high spin configuration. The electronic charge distribution analysis reveals that occupied e$_{\mathrm{g}}^{\mathrm{\ast }}$ states are well resonant with the host valence bands. As the e$_{\mathrm{g}}^{\mathrm{\ast }}$ states are located near the valence band maximum, Mn and Fe impurities are expected to enhance the p-type Seebeck coefficient of BST. [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T12.00010: Transport Properties of Ce, Sm, and Ho Doped Bismuth Antimony K.C. Lukas, H. Zhao, Z.F. Ren, C.P. Opeil Bi$_{\mathrm{88}}$Sb$_{\mathrm{12}}$ alloy has been doped with Ce, Sm, and Ho prepared under two different fabrication conditions. The first being ball milled for 12 hours and a hot pressed at 240 $^{\mathrm{o}}$C and the second ball milled for 6 hours and hot pressed at 200 $^{\mathrm{o}}$C. It is found that Ce, Sm, and Ho dopants all have a similar impact on the transport properties. A ZT enhancement is seen due to doping which is an effect of an enhanced Seebeck coefficient as a result of a decrease in the carrier concentration most likely caused by a widening band gap. The alteration of the band gap does not appear to be caused by the magnetic moments of Ce, Sm, and Ho based on the similar change to the gap size with the widely varying magnetic moments of the dopants. Also, similar results were not obtained with Fe doped samples, where Fe has a magnetic moment similar to Ce and greater than Sm. [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T12.00011: Low Temperature Transport Properties of Bi$_{2-x}$Tl$_{x}$Te$_3$ Single Crystals Hang Chi, Ctirad Uher, Petr Lostak, Cestmir Drasar We show that Tl-doping progressively changes the electrical conduction of Bi$_{2-x}$Tl$_{x}$Te$_3$ ($x=$0$-$0.30) single crystals from $p$-type (0$\le x\le $0.08) to $n$-type (0.12$\le x\le $0.30), which is observed via measurements of both the Seebeck coefficient and the Hall effect performed in the crystallographic \textit{ab}-plane in the temperature range of 2K-300K. The temperature dependent electrical resistivity in the \textit{ab}-plane of Bi$_{2-x}$Tl$_{x}$Te$_3$ maintains its metallic character with the decreasing hole density at low doping levels of 0$\le x\le $0.05. Heavier Tl-doping with 0.08$\le x\le $0.12 drives the electrical resistivity into a prominent non-metallic regime, associated with characteristic metal-insulator-metal transitions upon cooling down from 200K. For even more Tl-doped samples, 0.20$\le x\le $0.30, the system reverts back into the metallic state. Thermal conductivity measurements of Bi$_{2-x}$Tl$_{x}$Te$_3$ single crystals reveal a progressively stronger point defect scattering of phonon with the increasing Tl content. The systematic evolution of transport properties suggests that the Fermi level of Bi$_2$Te$_3$ which initially lies in the valence band (for $x=$0), is gradually shifted, with increasing Tl-doping, toward the top of the valence band (for 0.01$\le x\le $0.05), then into the band gap (for 0.08$\le x\le $0.10), and eventually into the conduction band (for 0.20$\le x\le $0.30). [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T12.00012: Valence band structure of Bi2Se3 Yi-Bin Gao, David Parker, Joseph P. Heremans Bi2Se3 is an interesting candidate for thermoelectric application because Se is a more abundant element than Te, which is commercially used in Bi2Te3-based Peltier coolers. However, intrinsic Se vacancies dominate in Bi2Se3 and dope the material n-type. Due to unfavourable conduction band structure, n-type Bi2Se3 does not have a high power factor. Recently, it has been calculated [1] that Bi2Se3 has a favourable valence band structure for thermoelectric application. In this presentation, high-quality p-type Bi2Se3 single crystals are prepared and Shubnikov de Haas measurement are carried out on them to characterize the band structure. Cross-sectional areas of Fermi surface are mapped out and compared with the theoretical calculation. Reference: [1] Phys. Rev. X 1, 021005 (2011) [Preview Abstract] |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T12.00013: Electronic and structural properties of superionic Cu$_{2}$Se from density functional theory Mikael R{\aa}sander, Lars Bergqvist, Anna Delin The superionic high temperature phase of Cu$_{2}$Se has been found to yield high thermoelectric efficiency due to an interesting combination of low thermal conductivity and a rather high power factor. The low thermal conductivity has been found to be due to the quasi-liquid behaviour of the superionic Cu atoms (Liu et al., Nature Materials, {\bf11}, 422-425 (2012)). Here we will present results obtained using density functional theory calculations of the electronic and structural properties of the superionic Cu$_{2}$Se phase. We will especially address how the inclusion of non-local exchange by the use of hybrid density functionals as well as how localization of the Cu 3d-states affect the electronic structure of Cu$_{2}$Se. [Preview Abstract] |
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