Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F12: Focus Session: Thermoelectric Materials and Applications |
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Sponsoring Units: DMP GERA FIAP DCOMP Chair: Lilia Woods, University of South Florida Room: 007C |
Tuesday, March 3, 2015 8:00AM - 8:12AM |
F12.00001: Thermoelectric energy harvester based on quantum well superlattices Yunjin Choi, Andrew Jordan We propose a nanoscale heat engine based on quantum well superlattices for harvesting thermal energy. A hot cavity is connected via superlattices to electronic reservoirs, and the electron transport through the superlattice by gaining energy from the hot cavity converts heat into electrical power. The energy gain is determined by the composite superlattices system. Therefore, the electric and heat current of electrons for simplified miniband transport of the superlattices give tunable conditions for the maximal generated power or efficiency. In addition, we analyze the phonon transport through the superlattices and show the reduction of the phonon thermal conductivity at high temperature which is beneficial for the highly efficient thermoelectric devices [1]. Combination of the electron and phonon transport shows an optimal configuration for the best performance of energy harvester. We discuss and compare our result with the energy harvester based on resonant quantum wells [2].\\[4pt] [1] M. V. Simkin and G. D. Mahan, Phys. Rev. Lett. \textbf{84}, 927 (2000).\\[0pt] [2] B. Sothmann, R. S\'{a}nchez, A. N. Jordan, and M. B\"{u}ttiker, New J. Phys. \textbf{15}, 095021 (2013). [Preview Abstract] |
Tuesday, March 3, 2015 8:12AM - 8:24AM |
F12.00002: Self-propagating high temperature synthesis for compound thermoelectrics and new criterion for applicability of combustion processing Xinfeng Tang, Xianli Su, Ctirad Uher Here we report compound thermoelectric materials (Bi$_{2}$Te$_{3}$, Bi$_{2}$Se$_{3}$, Cu$_{2}$Se, Cu$_{2}$SnSe$_{3}$, half-Heusler alloys, lead chalcogenides, skutterudites, and magnesium silicides) with thermoelectric properties comparable with materials prepared by the traditional routes of synthesis can be synthesized at a minimal cost and on the time scale of seconds using the self-propagating high temperature synthesis method. Moreover, we found that the criterion often quoted in the literature as the necessary precondition for combustion synthesis, $T_{\mathrm{ad}} \ge $ 1800 K, is not universal and certainly not applicable to thermoelectric compound semiconductors. Instead, we offer new empirically-based criterion, $T_{\mathrm{ad}}/T_{\mathrm{m,L}}$ \textgreater 1, i.e., the adiabatic temperature must be high enough to melt the lower melting point component, which covers all materials synthesized by self-propagating high temperature synthesis, including the high temperature refractory compounds for which the $T_{\mathrm{ad}} \ge $ 1800 K criterion was originally developed. Our work opens a new avenue for ultra-fast, low cost, mass production fabrication of efficient thermoelectric materials and the new criterion greatly broadens the scope of materials that can be successfully synthesized by self-propagating high temperature synthesis. [Preview Abstract] |
Tuesday, March 3, 2015 8:24AM - 8:36AM |
F12.00003: NbFeSb based p-type half-Heusler for power generation applications Giri Joshi, Ran He, Michael Engber, Georgy Samsonidze, Tej Pantha, Ekraj Dahal, Keshab Dahal, Jian Yang, Yucheng Lan, Boris Kozinsky, Zhifeng Ren We report a peak dimensionless figure-of-merit (ZT) of \textasciitilde 1 at 700 $^{o}$C in nanostructured p-type Nb$_{0.6}$Ti$_{0.4}$FeSb$_{0.95}$Sn$_{0.05\, }$composition. Even though the power factor of the Nb$_{0.6}$Ti$_{0.4}$FeSb$_{0.95}$Sn$_{0.05}$ composition is improved by 25{\%} in comparison to the previously reported p-type Hf$_{0.44}$Zr$_{0.44}$Ti$_{0.12}$CoSb$_{0.8}$Sn$_{0.2}$, the ZT value is not increased due to a higher thermal conductivity. However, the higher power factor of the Nb$_{0.6}$Ti$_{0.4}$FeSb$_{0.95}$Sn$_{0.05}$ composition led to a 15{\%} increase in power output of a thermoelectric device in comparison to a device made from the previous best material Hf$_{0.44}$Zr$_{0.44}$Ti$_{0.12}$CoSb$_{0.8}$Sn$_{0.2}$. The n-type material used to make the unicouple device is the best reported nanostructured Hf$_{0.25}$Zr$_{0.75}$NiSn$_{0.99}$Sb$_{0.01}$ composition with the lowest hafnium (Hf) content. Both the p- and n-type nanostructured samples are prepared by ball milling the arc melted ingot and hot pressing the finely ground powders. Moreover, the raw material cost of the Nb$_{0.6}$Ti$_{0.4}$FeSb$_{0.95}$Sn$_{0.05}$ composition is more than six times lower compared to the cost of the previous best p-type Hf$_{0.44}$Zr$_{0.44}$Ti$_{0.12}$CoSb$_{0.8}$Sn$_{0.2}$. This cost reduction is crucial for these materials to be used in large-scale quantities for vehicle and industrial waste heat recovery applications. [Preview Abstract] |
Tuesday, March 3, 2015 8:36AM - 9:12AM |
F12.00004: Automotive Thermoelectric Waste Heat Recovery Invited Speaker: Gregory P. Meisner Considerable fuel energy, as much as 70{\%}, is not converted to useful work by internal combustion engines but is instead rejected as waste heat, and more than half of the waste heat, nearly 40{\%} of fuel energy, is contained in vehicle exhaust gas. This provides an opportunity to recover some of the wasted fuel energy and convert it from heat into useful work, subject to the laws of thermodynamics, and thereby improve vehicle energy efficiency. Thermoelectric (TE) materials have been extensively researched and TE devices are now being developed for operation at high temperatures corresponding to automotive exhaust gases for direct solid-state conversion of heat into electricity. This has stimulated substantial progress in the development of practical TE generator (TEG) systems for large-scale commercialization. A significant enabler of this progress has been the US Department of Energy's Vehicle Technologies Program through funding for low cost solutions for automotive TE waste heat recovery to improve fuel economy. Our current project at General Motors has culminated in the identification of the potential supply chain for all components and assembly of an automotive TEG. A significant focus has been to develop integrated and iterative modeling tools for a fully optimized TEG design that includes all components and subsystems (TE modules, heat exchangers, thermal interfaces, electrical interconnects, power conditioning, and vehicle integration for maximal use of TEG power). We have built and tested a new, low-cost Initial TEG prototype based on state-of-the-art production-scale skutterudite TE modules, novel heat exchanger designs, and practical solutions to the many technical challenges for optimum TEG performance. We will use the results for our Initial TEG prototype to refine our modeling and design tools for a Final automotive TEG system prototype. Our recent results will be presented. Thanks to: J.R. Salvador, E.R. Gundlach, D. Thompson, N.K. Bucknor, M.G. Reynolds, K. Rober, F.R. Stabler; Marlow, JPL, Dana, Delphi E{\&}S, Eberspaecher, Molycorp, University of Washington, Purdue University, Michigan State University, ORNL, BNL. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:24AM |
F12.00005: Anharmonic phonons in type I clathrates Katsumi Tanigaki, Jiazhen Wu, Hidekazu Shimotani A systematic study on the anharmonicity of phonons is made for thermoelectric single crystal type-I clathrates based on their heat capacity $C_{p}$ at low temperatures (T) down to 360\,mK. The low-T linear terms $^{obs}\gamma T$ of $C_{p}$, including the tunneling-term of the atoms accommodated in the host cages ($\gamma_{ph} T$=$\alpha T$), and the Sommerfeld itinerant-electron term ($\gamma_{e} T$) are successfully separated through careful measurements of sigle crystals with various carrier concentrations. The values of the density of anharmonic potentials are deduced. The effective mass (m${*}$) enhancement is also determined from $\gamma_{e}$ values and the electron-phonon interaction strength ($\lambda$) can be evaluated from these values. It is shown that both the thermal conductivities ($\kappa$'s) and the electron-phonon interaction strengths ($\lambda$'s) are quantitatively in good agreement with the $\alpha$ parameters deduced from the present experiments. The boson peaks observed at low energy excitations are disucssued in relation to the $\alpha$ values. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 9:36AM |
F12.00006: Large local distortions around the Ba site in Ba$_{8}$Ga$_{16}$X$_{30}$, X=Si, Sn Trevor Keiber, Frank Bridges, Patrick Nast, Scott Medling, Toshiro Takabatake We report an Extended X-ray Absorption Fine Structure (EXAFS) analysis of thermoelectric type-I clathrates, Ba$_{8}$Ga$_{16}$X$_{30}$, X=Sn,Si. These clathrates have a cage-like crystal structure filled with ``rattler'' atoms (Ba) located near the center of the cages (Ga-X). In contrast to the results for Ba$_{8}$Ga$_{16}$Ge$_{30}$, our results show that for X=Sn,Si the average pair distances within the cages (Ga-Sn, Ga-Ga, Ga-Si, Sn-Sn) are significantly different than the average distances found from diffraction. Direct measurements of the Ba K edge suggests that the environment about Ba is very highly disordered for X=Sn,Si compared to X=Ge, with surprisingly short Ba-X/Ga distances; likely the Ba2 site is significantly off center. For Si, the Ba K first neighbor peak is substantially reduced in size and shifted to lower r due to interference effects from many different Ba neighbor distances. For X=Sn the Ba-Ga/Sn distances are even shorter, and there is a split peak with very low amplitude suggesting a very disordered environment. The mixed distances of the cage atoms, the very short Ba-Ga/X distances, as well as the disorder about the Ba site, suggest that the cage structure is buckled. This disorder will lead to increased scattering for both phonons and electrons. [Preview Abstract] |
Tuesday, March 3, 2015 9:36AM - 9:48AM |
F12.00007: Effect of Alkaline Metal Filling on the Structural Properties of Type-II Clathrate A$_{\mathrm{x}}$M$_{136} $(A $=$ Na,K,Rb,Cs; M $=$ Group IV Atom; 0$\le $ x$\le $ 24) Charles Myles, Dong Xue Early investigations of the properties of the Type II clathrate Na$_{\mathrm{x}}$Si$_{136}$ (0\textless x\textless 24) [1] have found that, as the composition x increases, the Si$_{136}$ lattice exhibits framework contraction upon filling (0\textless x\textless 8), followed by an expansion of the unit cell volume (9\textless x\textless 24). Stimulated by this discovery of a non-monotonic structural response to cage filling by the guests, we have performed a systematic, first-principles study the of the guest-framework interaction in the large and small cages in the Type II clathrates Si$_{136}$, Ge$_{136}$, and Sn$_{136}$. Our calculations are based on the VASP code and we have considered Na, K, Rb, and Cs guests for 0$\le $x$\le $24. An emphasis in our study is on how the guest atom size affects the dynamical behavior of the host material. We focus on the host lattice structural expansion or compression as x increases. We also present and discuss calculations of the effective potential energy curves for the guest-host interactions in these materials. Our results are correlated with the harmonic (or anhamonic) oscillations of the guests. These results are useful as an indication of the expected behavior of the guest ``rattling'' phonon modes in these materials. Among other results, we find that some guests are weakly bonded in the host cages and others are unstable around the cage centers. \\[4pt] [1] Beekman, Nenghabi, Biswas, Myles,~ Baitinger, Grin, Nolas,~Inorganic Chemistry~49,~5338~(2010). [Preview Abstract] |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F12.00008: First Principles Study of the Vibrational and Thermal Properties of the Type-II Clathrates A$_{\mathrm{x}}$Ga$_{\mathrm{x}}$Sn$_{\mathrm{136-x}}$(x $=$ 8,16,24; A $=$ Rb,Cs) Dong Xue, Charles Myles We have performed first-principles calculations of the vibrational and thermal properties of the semiconductor clathrates Rb$_{\mathrm{x}}$Ga$_{\mathrm{x}}$Sn$_{\mathrm{136-x}}$ and Cs$_{\mathrm{x}}$Ga$_{\mathrm{x}}$Sn$_{\mathrm{136-x}}$ for x $=$ 8, 16, and 24. Our calculations used the VASP code to obtain the equilibrium geometries and the PHONOPY code to obtain the harmonic phonon modes. For x $=$ 24, the phonon dispersion relations predict an upshift of the low-lying optical modes (\textless 30cm$^{\mathrm{-1}})$ in the presence of the light guest (``rattler'') Rb. We also find large isotropic atomic displacement parameters ($U_{\mathrm{iso}})$ when the Rb occupies the large cages (Sn$_{\mathrm{28}})$. The modes associated with these guests should contribute strongly to lowering the lattice thermal conductivity ($k_{L})$. This is reinforced by our evaluation of the guest-associated effective potential energy curves E(x). Our calculated effective harmonic spring constants K for these guests show that a simple harmonic oscillator model is in good agreement with the first principles lattice dynamical calculations. The similarity between $\omega_{\mathrm{os}}=$ (K/M)$^{1/2}$ and our computed guest phonon frequencies implies that anharmonic contributions to the guest vibrational modes are not significant. Our calculations of the vibrational contribution to the specific heat and our estimation of $k_{L} $are also presented and discussed. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F12.00009: Study on Transport and Mechanical Properties of La and Ce Double Filled $p$-type Skutterudites Tulashi Dahal, Sonika Gahalwat, Qing Jie, Hee Seok Kim, Keshab Dahal, Weishu Liu, Yucheng Lan, Kenneth White, Zhifeng Ren Optimizing the thermoelectric performance of $p$-type skutterudites is extremely challenging due to several factors such as low Seebeck voltage and bipolar contribution in electrical and thermal conductivity at elevated temperature, leading to small \textit{ZT }value. In this work, we report improved thermoelectric performance of La and Ce double filled $p$-type skutterudites by melting-quenching-annealing-ball milling-hot pressing. The observed high power factor ($\sim $35 $\mu $W cm$^{-1}$ K$^{-2}$ at 500 $^{\circ}$C) and low thermal conductivity ($\sim $2.5 W m$^{-1}$ K$^{-1}$ at 500 $^{\circ}$C) leads to a peak \textit{ZT} about 1.1 in the optimized composition. With a $\Delta T$ of 475 $^{\circ}$C between heat source and sink, the estimated output power density in the best sample is $\sim $8 W cm$^{-2}$. The nano-indentation experiment reveals that the hardness and Young's modulus of elasticity of the sample is much better than Bi$_{2}$Te$_{3}$ and PbTe-based samples, indicating skutterudites is suitable for practical applications where mechanical strength is also important. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F12.00010: Local structure in ball-milled and Ni substituted Nd$_y$Fe$_{4-x}$Ni$_x$Sb$_{12}$ Frank Bridges, Felipe Rivas, Markus Short, Trevor Keiber, Peter Rogl We report EXAFS measurements at the Nd L$_{\rm III}$, Fe, and Sb K edges in Nd$_y$Fe$_{4-x}$Ni$_x$Sb$_{12}$. Recent measurements show that ball-milled Nd$_y$Fe$_4$Sb$_{12}$, with $\sim$ 150 nm size particles, significantly improved the figure of merit (ZT) by 22 \%, compared to material with 10 $\mu$m sized particles. Since ball milling can produce significant disorder and even amorphization, which would lower the thermal conductivity, we compared the local structure for ball-milled and hand ground samples. We find that the average local structure is essentially unchanged by ball milling; the reduced particle size reduces the phonon mean free path, thereby reducing the thermal conductivity. When Ni is substituted on the Fe site, together with a decreased concentration of Nd, we find the largest changes in disorder are about the Nd atoms; there is little disorder of the first few neighbors about the Fe site. Further the local distortions are not uniform; the lattice constant decreases with Ni concentration, but the Nd-Sb bond length slightly expands while the Sb-Sb contracts more than expected. Some consequences are discussed. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F12.00011: Thermoelectric properties of GeTe-CuInTe$_{2}$ alloys Si Hui, James Salvador, Hui Sun, Kevin Pipe, Ctirad Uher GeTe-AgSbTe$_{2}$ and PbTe-AgSbTe$_{2}$ alloys, known as TAGS and LAST respectively, are excellent thermoelectric materials. By alloying the matrix with other ternary compounds, the thermal conductivity is significantly reduced due to the enhancement of phonon scattering by the formation of nano-sized secondary phases and disturbance to the lattice. Meanwhile, since the ternary compound AgSbTe$_{2}$ also exhibits good thermoelectric properties and Ag$^{+}$ and Sb$^{3+}$ tend to replace two Ge atoms at the same time, the mobility, and thus the power factor, will not be influenced much by this alloying. In this work, we replaced the ternary compound AgSbTe$_{2}$ by CuInTe$_{2}$ which does not contain the expensive element Ag and also exhibits good thermoelectric properties. We measured the Seebeck coefficient, electrical conductivity, thermal conductivity and Hall coefficient, and observed that CuInTe$_{2}$ almost has no influence on the power factor but does reduce the thermal conductivity. ZT was observed to improve to 1.2 at 800K for (Ge$_{2}$Te$_{2})_{0.97}$(CuInTe$_{2})_{0.03}$. We believe that ZT will be further enhanced at larger CuInTe$_{2}$ fractions due to further reduced thermal conductivity. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F12.00012: Thermoelectric and Lattice Dynamical Properties of Ge$_{2}$Sb$_{2}$Te$_{5}$ Saikat Mukhopadhyay, Jifeng Sun, Alaska Subedi, David Singh Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) has been widely used as phase-change materials in optical data storage media and nonvolatile RAM devices. At elevated temperature, GST is known to undergo subsequent structural transitions from a non-conducting amorphous to (metastable) disordered cubic phase and then to a conducting hexagonal phase above 300$^{\circ}$C. Given that hexagonal-GST has already been reported to have promising thermoelectric properties and transport properties critically depend on the bonding information, a direct correlation between its structural- and transport properties needs to be established. In this talk, we will present the evolution of thermoelectric and lattice dynamical properties of GST in different phases via first principles calculations based on density functional theory. A better understanding of the origin of low-thermal conductivity in hexagonal-GST may provide critical information for further improvement of its thermoelectric figure of merit (ZT). [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F12.00013: Calculation of Phonon Conductivity and Seebeck Coefficient in Cu-Ni Alloy Yusuke Konishi, Yoshihiro Asai In recent years, thermoelectric materials have been attracting a lot of attention because they are expected to be applied for utilization of waste heat. Many kinds of materials are studied for this purpose; semiconductors, alloys, organic materials, etc. In 2010, a giant Peltier effect was observed in a Cu-Ni/Au junction [1]. It is considered that this giant Peltier effect is caused by nano-scale phase separation formed in the sputtering process. Although this material is a great candidate for a thermoelectric material, we need to find the condition for a large thermoelectric coefficient that requires a large Seebeck coefficient, large electric conductivity, and small phonon conductivity. We calculated phonon conductivity in Cu-Ni alloy by using nonequilibrium molecular dynamics simulation and calculated Seebeck coefficients via ab-initio methods. [1] A. Sugihara et al., Appl. Phys. Exp. 3, 065204 (2010). [Preview Abstract] |
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