Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q28: Focus Session: Thermoelectricity in Bulk Materials |
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Sponsoring Units: DMP FIAP Chair: Joshua Zide, University of Delaware Room: Morial Convention Center 220 |
Wednesday, March 12, 2008 11:15AM - 11:51AM |
Q28.00001: Thermoelectric Transport Coefficients in Correlated Condensed Matter Invited Speaker: We present a recently developed formalism for computing thermoelectric transport coefficients for standard models of correlated matter, such as the Hubbard and the $t-J$ model. Successful predictions of this method in the context of the Hall constant are noted. This success helps to motivate the extension to the Seebeck coefficient, the Lorentz number L, and the figure of merit $Z T$, in terms of novel equal time correlation functions of two new fundamental operators, the thermal operator $\Theta^{xx}$ and the thermoelectric operator $\Phi^{xx}$. Along the way, we uncover a new sum rule for the dynamical thermal conductivity for many standard models, precisely analogous to the f-sum rule for the electrical conductivity. Also along the way, we throw light on Lord Kelvin's early ideas on reciprocity, worked out within the context of equilibrium thermodynamics. The precise connection between Kelvin's formulation, and the later and more rigorous formulation of Onsager is commented upon. The new formalism is tested in simple settings and recent computational results are displayed for testing the frequency dependence of these variables in certain standard models. Close agreement with existing transport experiments on sodium cobaltates $Na_{.68} Co O_2$ in the Curie Weiss phase is found. Finally some new predictions are made regarding triangular lattice systems, motivated by the sodium cobaltate system. [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q28.00002: Enhancing figure-of-merit of n-type Bi$_{2}$Te$_{3-x}$Se$_{x}$ Xiao Yan, Jian Yang, Yi Ma, Bed Poudel, Yucheng Lan, Dezhi Wang, Zhifeng Ren, Qing Hao, Gang Chen Themoelectric materials with high dimensionless figure-of-merit (ZT) are greatly demanded in energy industry, among which bismuth telluride (Bi$_{2}$Te$_{3})$ exhibits decent ZT around room temperature. However, thermal conductivity of Bi$_{2}$Te$_{3}$ is still high which limits its wider use for low temperature cooling devices. Here we investigate nanostructured bulk n-type Bi$_{2}$Te$_{3-x}$Se$_{x}$ by reducing the thermal conductivity via increased phonon scattering of the significantly increased grain boundaries due to nano size grains. We first make alloyed nanopowders by mechanical alloying a mixture of elements with the right ratio and then 100{\%} nanostructured samples by hot press. [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q28.00003: High pressure transport studies on Sb$_{2}$Te$_{3}$ and BiSbTe$_{3}$ Matthew Jacobsen, Andrew Cornelius Interest regarding the abilities of thermoelectric materials has produced exciting results regarding their properties in the thin-film form [3]. However, little work has been done regarding the pressure tuning of the thermoelectric figure of merit for these materials materials. Some previous work has suggested that it would be useful to investigate this further using pressure tuning [1],[2]. Based upon this interest, facilities have been developed in our laboratory for the study of the relevant properties under high pressure up to near 20 GPa. Results of this work on Sb$_{2}$Te$_{3}$ and BiSbTe$_{3}$ will be presented here from the use of these facilities. [1]Chen, G., Dresselhaus, M.S., Dresselhaus, G., Fleurial, J.-P., and Caillat, T. \emph{Recent developments in themoelectric materials}. International Materials Reviews, \textbf{48}, 45-66 (2003). [2]Rowe, D.M. \emph{CRC Handbook of Thermoelectric Materials}. CRC Press, 1995. [3]Venkatasubramanian, R., Silvola, E., Colpitts, T., and O'Quinn, B. \emph{Thin-film thermoelectric devices with high room-temperature figures of merit}. Nature, \textbf{413}, 597-602, 2001. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q28.00004: Inelastic scattering on antimony bearing thermoelectric materials: rattlers revisited R. P. Hermann, W. Schweika, H.-C. Wille Antimony element specific measurements on EuFe$_4$Sb$_{12}$ and Zn$_4$Sb$_3$ will be presented in parallel with inelastic neutron scattering measurements on Zn$_4$Sb$_3$. These results yield new insight in the rattler concept. First, the antimony specific DOS in EuFe$_4$Sb$_{12}$ and CoSb$_{3}$ provides experimental insight into the guest-host interaction mechanism which is required for a lowering of the thermal conductivity[1]. Second, the scattering vector dependence of the Zn$_4$Sb$_3$ inelastic response reveals that ''rattling'' behavior is not restricted to single atoms and that more complex structural units, such as dumbbells, can exhibit a similar behavior that is responsible for a low thermal conductivity.[2] [The European Synchrotron Radiation Facility is acknowledged for provision of the synchrotron radiation facility at beamlines ID18 and ID22N and the European Community - ARI HPRI-2001-00175 is acknowledged for provision of neutron scattering beam time at the FRJ-II research reactor in J\"ulich, Germany.] [1] Schweika W. et al. Phys. Rev. Lett. 99, 125501 (2007). [2] Wille H.-C. et al. Phys. Rev. B 76, 140301(R) (2007). [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q28.00005: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q28.00006: Lattice thermal conductivity of AgSbTe$_{2}$ Donald Morelli, Vladimir Jovovic, Suraj Thiagarajan, Joseph Heremans The lattice thermal conductivity of high-quality crystals of AgSbTe$_{2}$ is nearly temperature-independent from 80 to 300 K, and has a value of 0.65$\pm $0.05 W/mK. This value corresponds to the minimum possible thermal conductivity, where the phonon mean free path equals the interatomic distance. The result is analyzed in terms of scattering mechanisms: Umklapp and Normal phonon-phonon scattering processes are the dominant mechanism. It is, to our knowledge, the first system in which intrinsic phonon-phonon interactions limit the lattice thermal conductivity to such a low value. This in turn results from the extreme anharmonicity of the chemical bonding in AgSbTe$_{2}$, which gives rise to one of the highest Gr\"{u}neisen parameter of any solid. The phonon-phonon scattering rate being a function of the square of the latter, the lattice thermal conductivity is also one of the lowest. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q28.00007: Galvanomagnetic and thermomagnetic properties of AgSbTe$_{2}$ Vladimir Jovovic, Joseph Heremans We report here data on the electrical resistivity, magnetoresistance, Hall effect, thermoelectric power, magneto-Seebeck and transverse Nernst-Ettingshausen coefficients of high-quality crystals of AgSbTe$_{2}$, measured from 77 to 400 K in magnetic fields up to 2 Tesla. Thermal conductivity data are also reported in samples with a much higher carrier concentration than those used in our other work.$^{1}$ From an analysis of these data, we conclude AgSbTe$_{2}$ to be a very narrow-gap semiconductor (Eg$\approx $ 7.6$\pm $3 meV) with $\sim $5x10$^{19}$ cm$^{-3}$ holes in a valence band with a high density of states and thermally excited $\sim $10$^{17}$ cm$^{-3}$ high-mobility (2,200 cm$^{2}$/Vs) electrons at 300 K. The estimated hole density-of-states effective masses, including Fermi pocket degeneracy, is 2.5$\pm $0.5 free electron masses; the electron mass is about two orders of magnitude smaller, but the exact value cannot be resolved. The lattice term dominates the thermal conductivity, $^{1}$ and the electronic contribution in samples with both electrons and holes present is in turn dominated the ambipolar term. The low thermal conductivity and very large hole mass of AgSbTe$_{2}$ make it a most promising p-type thermoelectric material. [1] Lattice thermal conductivity of AgSbTe$_{2}$, D. T. Morelli, V. Jovovic, S. J. Tiagarajan, and J. P. Heremans, Abstract reported here. [Preview Abstract] |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q28.00008: De Haas - van Alphen quantum oscillations in AgSbTe$_{2}$ Joseph Heremans, Vladimir Jovovic Quantum oscillations are observed in the magnetic susceptibility of $p$-type single crystals of AgSbTe$_{2}$, at 5 K in magnetic fields up to 5 Tesla (the De Haas - van Alphen effect). The period of the oscillations is analyzed in terms of the cross-section of the hole Fermi surface. Recent band structure calculations$^{1}$ illustrate the dependence of the hole Fermi surface structure on the ordering of the Ag and the Sb atoms on the metal sublattice, and provide guidance for the interpretation of the periods of the oscillations. Galvanomagnetic studies of the same sample$^{2}$ provide a hole density of 5x10$^{19}$ cm$^{-3}$, so that an image for the valence band Fermi surface can be reconstructed at that carrier density level. The measured Fermi surface cross-sections, together with the transport properties, give an overall picture that is consistent with the calculation valid for AgSbTe$_{2}$ with Ag and Sb ordered on the metal sublattice. [1] Khang Hoang, S. D. Mahanti, James R. Salvador, and Mercouri G. Kanatzidis, Atomic Ordering and Gap Formation in Ag-Sb Based Ternary Chalcogenides, Phys. Rev. Lett. 2007, accepted [2] V. Jovovic and J. P. Heremans, Galvanomagnetic and Thermomagnetic properties of AgSbTe$_{2}$, abstract here [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q28.00009: Precipitation anneals in the PbTe-PbS system Christopher Jaworski, Vladimir Jovovic, Joseph Heremans Bulk samples of (PbS)$_{x}$(PbTe)$_{1-x}$ have been prepared in the range 4{\%}$<$x$<$15{\%}. There is a miscibility gap in the pseudo-binary PbTe/PbS phase diagram that enables the precipitation of a PbS-rich phase in a PbTe-rich matrix. To that effect, the samples were compounded in the liquidus, and then quenched, resulting in a supersaturated solution. Conditions for precipitation anneals were then developed, and samples with nano-precipitates of a PbS-rich phase in a PbTe-rich parent phase have been obtained, as evidenced by X-ray diffractions. This technique, previously applied to Pb-rich PbTe,$^{1}$ is aimed at creating a bulk material containing a substantial fraction of nanometer-sized particles in order to mimic the morphology of quantum-dot superlattices that reached very high values of the thermoelectric figure of merit.$^{2}$ Preliminary thermoelectric and thermal conductivity data will be presented, along with galvanomagnetic and thermomagnetic data aimed at identifying the electronic properties of the materials. [1] J. P. Heremans, C. M. Thrush and D. T. Morelli, Thermopower enhancement in PbTe with Pb precipitates, J. Appl. Phys. \textbf{98} 063703 (2005 [2] T. C. Harman, M. P. Walsh, B. E. LaForge, and G. W. Turner, J. Electron. Mater. \textbf{34}, L19 (2005). [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q28.00010: High-Resolution $^{125}$Te NMR of Novel Thermoelectric Materials E.M. Levin, K. Schmidt-Rohr, B.A. Cook, Mi-Kyung Han, M.G. Kanatzidis Several novel Te-based thermoelectric materials with extraordinary figure of merit \textit{ZT} $\ge $1.4 have been studied by high-resolution 25 kHz magic angle spinning $^{125}$Te nuclear magnetic resonance (NMR) in order to investigate variations in composition on the nano-scale. A 20-fold wider $^{125}$Te NMR signal of both AgSbGe$_{4}$Te$_{6}$ and AgSbGe$_{5.67}$Te$_{7.67}$ ($\sim $90 kHz) compared to that of PbTe (4.5 kHz) indicates a variation of shifts due to local composition fluctuations. The similar total shift of the main peak in Ag$_{0.53}$Pb$_{18}$Sb$_{1.2}$Te$_{20}$ (-1790 ppm) and PbTe (-1750 ppm) and similarly long T$_{2}$ relaxation time show that the majority of Te atoms in both materials has a similar environment. A second peak in Ag$_{0.53}$Pb$_{18}$Sb$_{1.2}$Te$_{20}$ at -1600 ppm shows the presence of a second type of Te site, accounting for $\sim $1/3 of all Te. These are apparently located in {\{}Ag,Sb{\}}-rich inclusions, as indicated by a much shorter T$_{2}$, which can be due to the effect of quadrupolar relaxation of $^{121}$Sb or $^{123}$Sb (spin 5/2 or 7/2, respectively) on $^{125}$Te. Our data confirm suggestions made by Hsu\textit{ et al., }Science (2004) and by Chen \textit{et al.}, Appl. Phys. Lett. (2005) about the presence of nano-scale inclusions in Ag$_{0.53}$Pb$_{18}$Sb$_{1.2}$Te$_{20}$, which result in low lattice thermal conductivity and high \textit{ZT}. [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 1:51PM |
Q28.00011: Substitution effects on the thermoelectric properties of Sr$_{2}$IrO$_{4}$ Yannick Klein, Ichiro Terasaki Layered cobalt oxides with the low-spin (LS) state, such as Na$_{x}$CoO$_{2}$ and Ca$_{3}$Co$_{4}$O$_{9}$, have shown a good potential as p-type materials for thermoelectric applications [1, 2]. Layered rhodium oxides are also characterized by a high Seebeck coefficient and a low metallic resistivity [3, 4]. The LS configuration of the transition metal is considered to be at the origin of this unusual property. We have investigated the thermoelectric properties of Sr$_{2}$IrO$_{4}$, which is isostructural to the superconductors La$_{2}$CuO$_{4}$ and Sr$_{2}$RuO$_{4}$. Contrary to the later ones, Sr$_{2}$IrO$_{4}$ is a semiconductor with a narrow gap and a weak ferromagnetic ground state (T$_{c}\approx $ 240K, M$_{s}\approx $ 0.14$\mu _{B}$/Ir) [5]. For polycrystalline samples, the resistivity is of the order of 10$\Omega $.cm and the thermoelectric power shows a broad maximum around 110K (S $\approx $ 300$\mu $V.K$^{-1})$ denoting the activation of minority carriers. In order to increase the carrier concentration, we tried many substitutions for Sr and Ir. Results of resistivity, thermoelectric power and susceptibility will be discussed. \newline [1] I. Terasaki\textit{ et al.}, Phys. Rev. B \textbf{56}, R12685 (1997). [2] A. C. Masset \textit{et al.}, Phys. Rev. B \textbf{62}, 166 (2000). [3] Y. Klein \textit{et al.}, Phys. Rev. B \textbf{73} 165121 (2006). [4] S. Shibasaki \textit{et al.}, Phys. Rev. B \textbf{74}, 235110 (2006). [5] G. Cao \textit{et al}, Phys. Rev. B \textbf{57}, R11039 (1998). [Preview Abstract] |
Wednesday, March 12, 2008 1:51PM - 2:03PM |
Q28.00012: Temperature - Concentration Phase Diagram from First Principles Calculations in P2-Na$_{x}$CoO$_{2}$ Ying S. Meng, Yoyo Hinuma, Gerbrand Ceder The unusual electronic and magnetic properties of Na$_{x}$CoO$_{2}$ are attracting considerable interest in recent years. At high sodium content, the system displays unusually strong thermoelectric effect and a low metallic resistance. In this paper, we present temperature - concentration phase diagram for Na$_{x}$CoO$_{2}$ (0.5 $<$= x $<$= 1) obtained with first principles method of the Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA) scheme, where charge on Co is delocalized. In comparison we will also present the results obtained from the GGA with Hubbard U correction (GGA+U) scheme, where charge on Co is completely localized, forming Co$^{3+}$ and Co$^{4+}$. The stable Na-vacancy ordering schemes at various concentrations obtained in this work will be compared and contrasted with available experimental observations. We will discuss the key interactions that determine the ground states and the order/disorder transition temperatures of these states, which is important for understanding the thermoelectric properties of these mixed valence oxides. [Preview Abstract] |
Wednesday, March 12, 2008 2:03PM - 2:15PM |
Q28.00013: ABSTRACT WITHDRAWN |
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