Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session X15: Thermoelectrics |
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Sponsoring Units: FIAP Chair: Paul von Allmen, NASA - Jet Propulsion Laboratory Room: LACC 405 |
Friday, March 25, 2005 8:00AM - 8:12AM |
X15.00001: Novel High Efficient Cooling Device Based on a Combination of Physical Processes Alex Mischenko, Neil Mathur The design of a novel and highly efficient cooling device is presented. It comprises several electrocaloric elements whose working temperatures vary across the device. These elements are separated by thermoelectric heat switches (Peltier devices). The heat switches are open when driven by a sufficiently large forward current. In the absence of this current the heat switch is closed and conducts heat passively. A reverse current enhances heat flow. This active mode of heat transfer increases the efficiency of the entire device. Simulations will be presented using electrocaloric elements and thermoelectric heat switches with realistic properties. UK patent pending. [Preview Abstract] |
Friday, March 25, 2005 8:12AM - 8:24AM |
X15.00002: Angle-resolved photoemission spectroscopy study of n-type Bi$_2$Te$_3$ Han-Jin Noh, H. Koh, S.-J. Oh, J.-H. Park, T. Valla, P. Johnson We have performed angle-resolved photoemission spectroscopy (ARPES) studies of $n$-type Bi$_2$Te$_3$, which is a classical thermoelectric compound that shows high figure of merit (ZT) at room temperature. Band dispersions for major high symmetry directions were obtained and all the conduction bands were determined from the ARPES data. An ellipsoidal electron pocket was identified and the result is compared with that of de Haas-van Alphen effect. We also estimate the ZT value from ARPES data and discuss the origin of the high ZT value in connection with electronic structure. [Preview Abstract] |
Friday, March 25, 2005 8:24AM - 8:36AM |
X15.00003: Atomistic modeling of thermoelectric properties of Bi2Te3 and Sb2Te3 Seungwon Lee, Paul von Allmen, Abhijit Shevade, Fabiano Oyafuso Low-dimensional structures with a high density of interfaces exhibit a large thermoelectric figure of merit. For example, a figure of merit ZT=2.5 was measured at 300 K in a Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattice. The design of thermoelectric materials with an even higher figure of merit is conceivable by exploiting the enhancement of the density of states in low dimensionality structures and optimizing the phonon scattering at interfaces to reduce the thermal conductivity. As a step toward modeling such structures, we have computed the thermoelectric properties of bulk Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$ using an atomistic empirical tight-binding method and the Boltzmann transport equation. The tight-binding parameters for the materials are fitted to first-principle band structure calculations. Using the band structures obtained with the tight- binding model and the relaxation time approximation for the scattering, the Seebeck coefficient, the electrical conductivity and the electronic and lattice contribution to the thermal conductivity of bulk Bi$_{2}$Te$_{3} $ and Sb$_{2}$Te$_{3}$ are calculated. The lattice contribution to the thermal conductivity is obtained from a Monte Carlo solution to the Boltzmann equation for phonons. [Preview Abstract] |
Friday, March 25, 2005 8:36AM - 8:48AM |
X15.00004: Atomistic simulation of nanostructure effects on thermoelectric properties in Si/Ge nanowires Haibin Su, Paul von Allmen, Seungwon Lee, Tahir Cagin, William Goddard III Experimental results on the thermal conductivity of superlattices demonstrate that the thermal conductivity of a superlattice can be much lower than that estimated from the bulk values of its constituent materials, and even smaller than the thermal conductivity of the equivalent composition alloys. The thermal conductivity reduction, coupled with the possible increase of the Seebeck coefficient and electrical conductivity due to quantum confinement effects in these superlattices, makes the Si/Ge superlattice system a good candidate for highly efficient thermoelectric energy conversion. Here we will combine tight-binding and atomistic molecular dynamics approaches to study the effects of nano- patterning on thermoelectric properties. The lattice contribution to the thermal conductivity, which is dominant in semiconductors, will be obtained from a Green Kubo relationship. We will calculate the electrical conductivity, the electronic contribution to the thermal conductivity, and the Seebeck coefficient using linear response theory with the empirical tight binding approach, which is suitable for the study of self-assembled nanostructures containing millions of atoms. Finally, we will discuss the systematic engineering of nanostructure to improve the figure of merit. [Preview Abstract] |
Friday, March 25, 2005 8:48AM - 9:00AM |
X15.00005: Correlating thermoelectric efficiency with nanowire diameter for electrodeposited Bismuth Telluride nanowire arrays. Erik Menke, Reg Penner Physicists have predicted that the thermoelectric figure-of-merit (ZT) for a given material will increase as the material dimension is reduced from 3 to 2 to 1. However, there have been few experimental tests of these predictions because of the difficulties associated with synthesizing the nanowires and in making high quality measurements of ZT. We have devised a method for preparing arrays of very long n- and p-type Bi$_{2}$Te$_{3}$ nanowires with diameters ranging from 80 to 250 nm. These nanowires are prepared using electrochemical step edge decoration on graphite and then transferred to the surface of an electrical and thermal insulator. High quality measurements of ZT are possible on these transferred nanowire arrays, and the results of these measurements will be reported in this presentation. [Preview Abstract] |
Friday, March 25, 2005 9:00AM - 9:12AM |
X15.00006: Transport properties of germanium-filled skutterudites Jihui Yang, George Nolas, Hirotsugu Takizawa We report the transport properties of dense polycrystalline Ge-filled skutterudites Ge$_{0.25}$Co$_{4}$Sb$_{12}$ and Ge$_{0.05}$Co$_{4}$Sb$_{12}$ prepared by a high-pressure synthesis approach. Low temperature electrical resistivity, Seebeck coefficient, Hall coefficient, and thermal conductivity measurements were performed on these skutterudite compounds, and are compared with those of Co$_{4}$Sb$_{11}$Ge and CoSb$_{3}$. The Ge atoms residing inside the interstitial voids of the skutterudite crystal structure act as electron donors. The lattice thermal conductivity of these compounds is lower than that of CoSb$_{3}$ but higher than that of other filled skutterudites. The potential for thermoelectric applications is also discussed. [Preview Abstract] |
Friday, March 25, 2005 9:12AM - 9:24AM |
X15.00007: Growth and Characterization of Bi$_2$Te$_3$ Nanowires Srividya Natarajan, Matt Craps, Rahul Rao, Terry Tritt, Apparao Rao Bulk Bi$_{2}$Te$_{3}$ is one of the best known thermoelectric materials with a ZT $\sim $1 at room temperature. Theoretical studies have suggested that low-dimensional materials may exhibit ZT values that exceed 1. In this study, we use the pulsed laser deposition method to prepare Bi$_{2}$Te$_{3}$ nanowires by ablating a rotating Bi$_{2}$Te$_{3}$ target in an inert atmosphere. Si substrates are pretreated with poly-l-lysine to form an adhesion layer for 10 nm colloidal Au particles which serve as catalyst seed particles for the growth of the nanowires. Results from electron microscopy, electrical transport measurements and vibrational spectroscopic studies will be presented. [Preview Abstract] |
Friday, March 25, 2005 9:24AM - 9:36AM |
X15.00008: Thermal Transport in Silicon From Empirical Interatomic Potentials D. A. Broido, A. Ward, N. Mingo The accurate description of thermal transport of phonons in bulk and low-dimensional semiconductors is of central importance to the understanding of their thermoelectric properties. We present calculations of the lattice thermal conductivity of silicon based on several commonly used empirical models of the interatomic potential [1-3]. Second and third order force constants obtained from these potentials are used as inputs to an exact iterative solution to the phonon Boltzmann equation, which includes the anharmonic phonon-phonon scattering as well as isotopic defect and boundary scattering. Comparisons are made to available experimental data. The lattice thermal conductivity obtained from each model is not satisfactory, and suggestions for improvements are presented.\\ \\ \noindent [1] F. Stillinger and T. Weber, Phys. Rev. B 31, 5262 (1985).\\ \noindent [2] J. Tersoff, Phys. Rev. B38, 9902 (1988).\\ \noindent [3] J. F. Justo, M. Z. Bazant, E. Kaxiras, V. V. Bulantov, and S. Yip, Phys. Rev. B58, 2539(1998).\\ [Preview Abstract] |
Friday, March 25, 2005 9:36AM - 9:48AM |
X15.00009: Thermoelectric and Magnetoelectric Behavior in Gd$_5$Si$_2$Ge$_2$ and Piezoelectric Laminates Nersesse Nersessian, Scott McCall, Harry Radousky, Vitalij Pecharsky, Gregory Carman A laminate of Gd$_{5}$Si$_{2}$Ge$_{2}$ and PZT-5H exhibiting the thermoelectric and magnetoelectric effects was manufactured. Gd$_{5}$Si$_{2}$Ge$_{2}$ exhibits a strain resulting from either a thermally or magnetically induced phase transformation while PZT-5H generates a voltage resulting from an applied strain. Mechanically coupling the two phases by lamination gives rise to the thermoelectric and magnetoelectric effects. Thermoelectric properties were investigated by thermally cycling the laminate from 260K to 300K under a series of constant magnetic fields from 0T to 9T. Magnetoelectric properties were investigated by isothermally cycling the laminate in magnetic fields varying from 0T to 9T at 260K, 280K and 300K. [Preview Abstract] |
Friday, March 25, 2005 9:48AM - 10:00AM |
X15.00010: Thermal conductance of interfaces between highly dissimilar materials Ho-Ki Lyeo, David Cahill Understanding the thermal conductance of interfaces G is important for improving our knowledge about interlayer heat transport in multi-layer thermoelectric devices. Previously G for interfaces between highly dissimilar materials such as Pb/diamond and Pb/Al$_{2}$O$_{3}$ was measured by Stoner and Maris and found to be much higher than the radiation limit; the radiation limit G=$\frac{\pi }{3}\frac{k_B \nu _{\max }^3 }{c^2}$ is the maximum thermal conductance predicted by theory, where $\nu _{\max } $is the cutoff vibrational frequency of the metal and $c$ is the Debye velocity of the substrate. We report data for G between Pb or Bi and several substrates; diamond, hydrogen(H)-terminated diamond, sapphire, SiO$_{2}$/Si, H-terminated Si, and BeO/Be. The thermal conductance G is obtained by analyzing in-phase and out-of-phase signals from pump-probe measurements of thermoreflectance using a mode-locked Ti:sapphire laser. Measured values at room temperature are 16-29 MW/m$^{2}$/K for Pb (a factor of 2 smaller than previously reported) and 15-20 MW/m$^{2}$/K for Bi; i.e, the measured values of G exceed the radiation limit by a factor of 3-7, and are nearly independent of the substrate. [Preview Abstract] |
Friday, March 25, 2005 10:00AM - 10:12AM |
X15.00011: Transport and Thermoelectric Properties of Ca$_3$Co$_4$O$_9$ Thin Films Yufeng Hu, Qiang Li, Weidong Si, Eli Sutter, Robert Sabatini It has been discovered recently that cobaltates have very large thermoelectric power, which shows that cobaltates hold great promise to be potential integrated heating spreading solution, such as thermal management of microprocessors. Among the cobaltates, Ca$_{3}$Co$_{4}$O$_{9}$ and Ca$_{2}$Co$_{2}$O$_{5}$ are exhibiting best thermoelectric properties. The \textit{ZT} value for these calcium-cobaltates reaches as high as 2.7 at $T \quad \ge $ 873 K, which clearly challenges the best conventional thermoelectric materials found in intermetallic compounds, such as Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ alloys. The purpose of this work is to study the transport and thermoelectric properties of Ca$_{3}$Co$_{4}$O$_{9}$ thin films. We have successfully grown the Ca$_{3}$Co$_{4}$O$_{9}$ c-axis orientated thin films using Pulsed Laser Deposition (PLD) technique on various substrates, including Si, LaAlO$_{3}$, Al$_{2}$O$_{3}$. The resistivity and thermoelectric power measurements show that these films have superior thermoelectric properties, similar to that found in the bulk samples. The detailed transport and thermoelectric properties of Ca$_{3}$Co$_{4}$O$_{9}$ thin films will be discussed. This work was supported by the U. S. Dept. of Energy, Office of Basic Energy Science, under contract No. DE-AC-02-98CH10886. [Preview Abstract] |
Friday, March 25, 2005 10:12AM - 10:24AM |
X15.00012: Electronic structure and transport properties of high performance thermoelectrics AgPb$_{m}$SbTe$_{2+m}$$^{\dagger}$ D. I. Bilc, S. D. Mahanti, M. G. Kanatzidis {\it Ab initio} electronic structure calculations based on gradient corrected density functional theory were performed on a class of novel quaternary compounds AgPb$_{m}$SbTe$_{2+m}$,$^{2} $ which were found to be excellent high temperature thermoelctrics with large figure of merit {\it ZT} $\sim$2.2 at 800K.$^{3}$ These systems form in the rock-salt structure similar to the well known two component system PbTe where Ag and Sb occupy Pb sites. We find that resonant states appear near the top of the valence and bottom of the conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be understood in terms of modified Te-Ag(Sb) bonds. We find that the electronic structure near the gap depends sensitively on the microstructural arrangements of Ag-Sb atoms. The common feature of these microstructural arrangements is that they have a more rapidly increasing density of states (DOS) near the gap as compared to bulk PbTe due to the appearance of distinct resonant states. The effect of the increased DOS on the transport properties (electrical conductivity and thermopower) will also be discussed. 2. K. F. Hsu {\it et. al.}, Science {\bf 303}, 818, (2004). 3. D. I. Bilc {\it et. al.}, Phys. Rev. Letters {\bf 93}(14), 146403, (2004). $^{\dagger}$Supported by the Office of Naval Research (Contract No. N00014-02-1-0867 MURI program). [Preview Abstract] |
Friday, March 25, 2005 10:24AM - 10:36AM |
X15.00013: Mean square atomic displacements of LaFe$_4$Sb$_{12}$ Joseph Feldman, David Singh Calculations in the harmonic approximation of the mean square atomic displacements (MSDs) for the filled skutterudite, LaFe$_4$Sb$_{12}$, are discussed, where the first-principles based force constant model that we recently proposed for this material is employed.$^1$ The various values of MSDs at high temperatures are as expected, following the differences in coordination and short range force constants. The results are primarily compared with temperature dependent neutron diffraction measurements$^2$ of MSDs in La$_{.75}$Fe$_3$CoSb$_{12}$. The differences between theory and experiment are interpreted in terms of static disorder contributions to the MSDs. In the case of the isotropic MSDs, the resulting static disorder contributions are comparable to the corresponding {\it minimum} values previously obtained$^2$ from a data analysis, and both the Sb and Fe values are small compared to the La value of 0.0045\AA$^2$. Nevertheless the anisotropy in the Sb static disorder is large on the basis of our analysis, and in the direction of the neighboring La site the Sb disorder parameter is comparable to the above value for La. Finally, the effect of La interactions on the Sb- and Fe-MSDs is discussed within the context of our model, as is an Einstein model, fitted to the calculated La MSD.\\~\\1. J.L. Feldman et al., Phys. Rev. B {\bf 68}, 094301 (2003).\\2. B.C. Chakoumakos et al., Acta Cryst. B {\bf 55},341 (1999). [Preview Abstract] |
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