Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L25: Focus Session: Thermoelectric Materials |
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Sponsoring Units: GERA DMP Chair: Eric Toberer, Colorado School of Mines Room: 503 |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L25.00001: High throughput search for thermoelectric materials. Computational stability, transport and doping properties Invited Speaker: Georg K.H. Madsen Thermoelectric materials can be utilized for an efficient conversion of waste heat to electric power. While thermoelectric properties of known compounds can be rationalized and predicted using only the structure as an input [1], it turns out that a large number of semiconductor structures show potential for favorable thermoelectric properties [2]. This leaves the feasibility of achieving the optimal doping [3] and a low thermal conductivity as key bottlenecks in discovering new thermoelectric materials. In this talk I will discuss simple procedures to screen for these properties and illustrate this by the discovery of an industrially relevant thermoelectric material.\\[4pt] [1] L. Bjerg, G. K. H. Madsen, B. B. Iversen, Chem. Mater. 2011, 23, 390 \\[0pt] [2] I. Opahle, A. Parma, E. J. McEniry, R. Drautz, G. K H Madsen, New J. Phys., 2013, 15, 105010 \\ [0pt] [3] L. Bjerg, G. K. H. Madsen, B. B. Iversen, Chem. Mater. 2012, 23, 390 [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L25.00002: Thermoelectric Power Factor Enhancement in Tetrahedrites Xu Lu, Donald Morelli, Yongsheng Zhang, Chris Wolverton We report a strategy for power factor enhancement of the thermoelectric properties of Cu$_{12}$Sb$_{4}$S$_{13}$ tetrahedrites. Our previous strategy to improve the figure of merit in tetrahedrites was to reduce the electronic thermal conductivity at the expense of reducing the power factor by replacing monovalent Cu with divalent Zn or Fe. Here, we substitute S with Se, which is isovalent with S and therefore does not induce a doping effect. However, we observe a reduction in electronic resistivity in Cu$_{12}$Sb$_{4}$S$_{13-x}$Se$_{x}$ without affecting the thermopower, which leads to at least a 20{\%} enhancement in power factor. Furthermore, the substitution of S with Se causes a reduction in the lattice thermal conductivity via a solid solution effect, keeping the total thermal conductivity unchanged. Density Functional Theory (DFT) calculations indicate a narrowing of the band gap in Cu$_{12}$Sb$_{4}$Se$_{13\, }$relative to the sulfide; however, DFT also shows that the pure selenide is not thermodynamically stable. But Cu$_{12}$Sb$_{4}$S$_{13-x}$Se$_{x}$ single phase materials may be synthesized up to at least x $=$ 3. We believe this strategy will introduce additional degenerate energy levels near the top of valence band. Further studies should be performed to investigate the optimal Se concentration and its effect on figure of merit. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L25.00003: Structurally complex Zintl compounds for high temperature thermoelectric power generation Alexandra Zevalkink, Gregory Pomrehn, Zachary Gibbs, Jeffrey Snyder Zintl phases, characterized by covalently-bonded substructures surrounded by highly electropositive cations, exhibit many of the characteristics desired for thermoelectric applications. Recently, we demonstrated promising thermoelectric performance ($zT$ values between 0.4 and 0.9) in a class of Zintl antimonides that share a common structural motif: anionic moieties resembling infinite chains of linked tetrahedra. These compounds ($A_5M_2$Sb$_6$ and $A_3M$Sb$_3$ compounds where $A$ = Ca or Sr and $M$ = Al, Ga and In) crystallize as four distinct, but closely related chain-forming structure types. Their large unit cells lead to exceptionally low lattice thermal conductivity due to the containment of heat in low velocity optical phonon modes. Here, we show that chemical substitutions on the $A$ and $M$ sites can be used to control the electronic and thermal transport properties and optimize the thermoelectric figure of merit. Doping with alio-valent elements allows for rational control of the carrier concentration, while isoelectronic substitutions can be used to fine-tune the intrinsic properties. A combination of Density Functional calculations and classical transport models was used to explain the experimentally observed transport properties of these compounds. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L25.00004: Crystal structure and thermoelectric properties of kuramite Cu$_{3}$Sn(Se,S)$_{4}$ with cation disorder Yosuke Goto, Yoichi Kamihara, Masanori Matoba Ternary or quaternary compounds Cu$_{2}$--$T_{M}$--A--\textit{Ch}$_{4}$ ($T_{M}$; transition metal, A; group 14 or 15 elements, \textit{Ch}; chalcogen) are promising $p$--type thermoelectric materials because of their heavy but still conducting valence band, which is composed of Cu 3$d$ and Ch 3$p$ orbitals. Lattice thermal conductivity should be suppressed by cation disorder, however, coexistence of transition metals such as Cu and Zn on quaternary compounds complicate the understanding of the details of cation disorder by means of conventional X-ray diffraction. In this work, We demonstrate the crystal structure and thermoelectric properties of kuramite Cu$_{3}$Sn(Se,S)$_{4}$. Structural analysis revealed that polycrystalline samples crystallize in tetragonal $I$--42$m$ space group. The 2$a$ site was occupied by Cu only, while 2$b$ and 4$d$ sites were occupied by Cu and Sn partial disorder. Both electrical conductivity ($\sigma )$ and Seebeck coefficient ($S)$ were increased with substitution of Se for S, resulting $\sigma =$ 5.68 $\times$ 10$^{2}$ Scm$^{-1}$ and $S =$ 114 $\mu $VK$^{-1}$ at 623 K, respectively. At the conference, we will also report the alloy effect on thermal conductivity of Cu$_{3}$Sn(Se,S)$_{4}$ solid solution. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L25.00005: Carrier concentration optimization and Band convergence of Mg$_{2}$Si$_{\mathrm{1-x}}$Sn$_{\mathrm{x}}$ thermoelectric materials Xinfeng Tang, Wei Liu, Xianli Su, Ctirad Uher In our research, the optimization of electron concentration and the tuning of conduction band structure are explored in order to push it for application in power generation. Systematical experiments indicate that the appropriate over-stoichiometry of Mg content is beneficial to the adjustment of electron concentration in n-type Mg$_{2}$Si$_{\mathrm{1-x}}$Sn$_{\mathrm{x}}$ solid solutions. Moreover, the electron concentration of Mg$_{2}$Si$_{\mathrm{1-x}}$Sn$_{\mathrm{x}}$ is validly controlled by doping Sb or Bi with the combination of proper over-stoichiometry of Mg. First-principles calculations of the band structure and plentiful experimental researches proved that the bottom of the conduction band of Mg$_{2}$Si$_{\mathrm{1-x}}$Sn$_{\mathrm{x}}$ is characterized a double band structure, including a heavy band and a light band which converged in energy with the increase of the Sn/Si ratio and further degenerated at x $=$ 0.65 $\sim $ 0.68. Consequently, the convergence and degeneration of two conduction bands give rise to remarkable elevation on the carrier effective mass and Seebeck coefficient without a detrimental effect on the carrier mobility, and therefore lead to a largely enhanced power factor. Due to the optimization of both the electron concentration and conduction band structure, n-type Mg$_{2}$Si$_{\mathrm{1-x}}$Sn$_{\mathrm{x}}$, being provided with electron concentration in the range of 1.6 $\times$ 10$^{20}$ $\sim $ 2.5 $\times$ 10$^{\mathrm{20}}$ cm$^{-3}$ and x $=$ 0.6 $\sim $ 0.7, show the highest \textit{ZT} values of 1.3 at around 725 K and average \textit{ZT} values about 1.0 within 500 $\sim $ 800 K. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L25.00006: Electronic structure of defects in Mg$_2$Si and Cu$_3$SbSe$_4$ and their thermoelectric significance S.D. Mahanti, Dat Do Defects play an important role in the thermoelectric properties of narrow band gap semiconductors. Recently, Mg$_2$Si and its solid solutions with Mg$_2$Sn have been found to be excellent n-type thermoelectrics and have been studied extensively due to its unique feature called conduction band convergence [Liu et al., PRL 108, 166601 (2012)]. In this talk we will discuss the physics of defects in Mg$_2$Si and explore the possibilities of improving its thermoelectric properties by co-doping, using first principle calculation and supercell model. In addition, we will also discuss some of our results using the same approach on the nature of defects in another important thermoelectric system Cu$_3$SbSe$_4$ where the lone pairs of Sb control the nature of states near the band gap [Dat Do et al., J. Phys.: Condens. Matter 24, 415502 (2012)]. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L25.00007: Optimally doped hybridization gap semiconductor FeGa$_{3}$ as potential thermoelectric alloy* Vijayabarathi Ponnambalam, Donald T. Morelli FeGa$_{3}$, a hybridization gap semiconductor with a band gap of $\sim$ 0.5 eV can be a potential thermoelectric material if optimally doped. Due to the involvement of d-band in the transport, high Seebeck coefficient is a possibility. To achieve the optimum doping level, Mn, Co and Zn containing FeGa$_{3}$ alloys are being prepared either via the flux or solid state reaction method. Phase characterization will be carried out. Electrical and transport properties including resistivity, Seebeck and Hall coefficients and thermal conductivity will be measured over a wide temperature range of 80- 1000 K. These results will be presented and the potential of these compositions as thermoelectrics will be discussed.\\[4pt] *This work was supported as part of the Center for Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001054. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L25.00008: Alkaline earth lead and tin compounds $Ae_2$Pb, $Ae_2$Sn, $Ae$=Ca,Sr,Ba, as thermoelectric materials David Parker, David Singh We present a detailed theoretical study of three alkaline earth compounds Ca$_2$Pb, Sr$_2$Pb and Ba$_{2}$Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca$_2$Sn, Sr$_{2}$Sn and Ba$_{2}$Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L25.00009: High-temperature Thermoelectric Properties of Ag$_{2}$Se$_{0.5}$Te$_{0.5}$ Fivos Drymiotis, Tristan Day, David Brown, Nicholas Heinz, G. Jeffrey Snyder We will be presenting the high-temperature thermoelectric properties of Ag$_{2}$Se$_{0.5}$Te$_{0.5}$. This particular alloy displays very low thermal conductivity and competitive thermoelectric performance. Specifically, in the temperature region from 520 K to 620 K we observe non-hysteretic behavior between the heating and cooling curves and zT values ranging from 1.2 to 0.8. Higher zT values are observed at lower temperatures on cooling. Our results suggest that this alloy is a competitive thermoelectric material for intermediate temperature power generation applications. The authors would like to thank the U.S. Air Force Office of Scientific Research for supporting this work. [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L25.00010: Skutterudite Derivatives: A Fundamental Investigation of New Materials with Potential for Thermoelectric Applications Kaya Wei, Yongkwan Dong, George Nolas Thermoelectric devices allow for the direct conversion of heat into electricity as well as solid-state refrigeration. Skutterudites continue to be of great interest for power generation applications. For example, when atoms are placed into the interstitial cages of these open-structured materials, the lattice thermal conductivity can be substantially reduced compared with that of unfilled skutterudites. Recently we began a fundamental investigation of new compounds with a modified skutterudite structure. Fundamental studies on the synthesis and low temperature transport properties of unfilled and partially filled rhombohedrally modified skutterudite derivatives will be presented. Along with Reitveld refinement, the structure and stoichiometry of those compositions as well as their transport properties will be discussed. This work aims to further the fundamental investigation of new skutterudites, while continuing the research on these materials towards thermoelectric power generation applications. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L25.00011: Synthesis and thermoelectric property of Ca and In-doped n-type Bi$_{85}$Sb$_{15}$ alloy Kamal Kadel, Wenzhi Li, Giri Joshi, Zhifeng Ren In the present work we investigated the thermo-electric properties of undoped Bi$_{85}$Sb$_{15}$ and different Ca-doped Bi$_{85}$Sb$_{15}$Ca$_{x}$ (x$=$0.5, 2, and 5) and In-doped Bi$_{85}$Sb$_{15}$In$_{\mathrm{x}} $(x$=$0.5, 2) alloys synthesized via arc-melting first and followed by ball milling and hot pressing. Effect of different Ca and In doping levels on transport properties of Bi$_{85}$Sb$_{15}$ alloys has been investigated. It is found that thermal conductivity decreases with increasing Ca and decreasing In. Electrical transport measurements show that power factor increases with doping level of Ca up to Bi$_{85}$Sb$_{15}$Ca$_{2}$ and then decreases yielding the maximum power factor of 3.8 $\times$ 10$^{-3}$ Wm$^{-1}$K$^{-2}$ and zT of 0.39 at room temperature for Bi$_{85}$Sb$_{15}$Ca$_{2}$. For indium doping, power factor decreases with doping level from 0.5 to 2, yielding the maximum zT value of 0.37 at room temperature for Bi$_{85}$Sb$_{15}$In$_{0.5}$. In this work, calcium doping in Bi$_{85}$Sb$_{15}$ alloy is found to yield better thermoelectric property than indium doping. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L25.00012: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L25.00013: Small-polaron transport and thermoelectric properties of the misfit-layer composite (BiSe)$_{109}$TaSe$_{2}/$TaSe$_{2}$ Jin-hee Kim, Yoo Jang Song, Jong-Soo Rhyee, Bong-Seo Kim, Su-Dong Park, Hyeung Jin Lee, Jae-Wook Shin We studied the thermoelectric properties of the composite of misfit-layered compounds (BiSe)$_{109}$TaSe$_{2}$ and TaSe$_{2}$. The x-ray diffraction pattern on the cross-sectional plane of the sintered body shows a preferred orientation of the (00$l)$ direction for (BiSe)$_{109}$TaSe$_{2}/$TaSe$_{2}$ indicating anisotropic alignment during hot pressing. Because of the crystallographic alignment, the temperature-dependent electrical resistivity $\rho (T )$, Seebeck coefficient $S(T )$, and the thermal conductivity $\kappa (T)$ exhibit in-plane and out-of-plane anisotropic transport behavior. The Seebeck coefficient is very low because of the coexistence of electron and hole mixing, as confirmed by the two-carrier model. The lattice thermal conductivity $\kappa_{L} $of the covalent bonding layer (in-plane) is lower than those of the layer with van der Waals bonding (out-of-plane) implying the existence of a charge density wave along the in-plane. We observed a sign anomaly of the positive Hall coefficient $R_{H}$ and negative Seebeck coefficient $S$. According to Holstein's small-polaron model, the sign anomaly may come from the odd number of small-polaron hopping sites. [Preview Abstract] |
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