Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N12: Focus Session: Thermoelectrics Materials Waste Heat |
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Sponsoring Units: DMP GERA FIAP Chair: Brian Sales, ORNL Room: 314 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N12.00001: On the thermodynamics of waste heat recovery from internal combustion engine exhaust gas G.P. Meisner The ideal internal combustion (IC) engine (Otto Cycle) efficiency $\eta _{\mathrm{IC}}=$ 1-(1/r)$^{(\gamma -1)}$ is only a function of engine compression ratio r$=$V$_{\mathrm{max}}$/V$_{\mathrm{min}}$ and exhaust gas specific heat ratio $\gamma =$ c$_{\mathrm{P}}$/c$_{\mathrm{V}}$. Typically r$=$ 8, $\gamma =$ 1.4, and $\eta_{\mathrm{IC}}=$ 56{\%}. Unlike the Carnot Cycle where $\eta _{\mathrm{Carnot}}=$ 1-(T$_{\mathrm{C}}$/T$_{\mathrm{H}})$ for a heat engine operating between hot and cold heat reservoirs at T$_{\mathrm{H}}$ and T$_{\mathrm{C}}$, respectively, $\eta_{\mathrm{IC}}$ is not a function of the exhaust gas temperature. Instead, the exhaust gas temperature depends only on the intake gas temperature (ambient), r, $\gamma $, c$_{\mathrm{V}}$, and the combustion energy. The ejected exhaust gas heat is thermally decoupled from the IC engine and conveyed via the exhaust system (manifold, pipe, muffler, etc.) to ambient, and the exhaust system is simply a heat engine that does no useful work. The maximum fraction of fuel energy that can be extracted from the exhaust gas stream as useful work is (1-$\eta_{\mathrm{IC}}) \times \eta_{\mathrm{Carnot}}=$ 32{\%} for T$_{\mathrm{H}}=$ 850 K (exhaust) and T$_{\mathrm{C}}=$ 370 K (coolant). This waste heat can be recovered using a heat engine such as a thermoelectric generator (TEG) with $\eta_{\mathrm{TEG}}$\textgreater\ 0 in the exhaust system. A combined IC engine and TEG system can generate net useful work from the exhaust gas waste heat with efficiency $\eta _{\mathrm{WH}}=$ (1-$\eta_{\mathrm{IC}}) \times \eta _{\mathrm{Carnot}} \times \eta_{\mathrm{TEG}}$, and this will increase the overall fuel efficiency of the total system. Recent improvements in TEGs yield $\eta_{\mathrm{TEG}}$ values approaching 15{\%} giving a potential total waste heat conversion efficiency of $\eta _{\mathrm{WH}}=$ 4.6{\%}, which translates into a fuel economy improvement approaching 5{\%}. [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N12.00002: Synthesis of High Performance Thermoelectric Materials Directly from Natural Mineral Xu Lu, Donald Morelli, Yi Xia, Fei Zhou, Vidvuds Ozolins, Hang Chi, Xiaoyuan Zhou, Ctirad Uher We report high performance TE materials synthesized directly from natural mineral. Lattice dynamics and electronic band structure calculations suggest that the compound tetrahedrite (Cu$_{\mathrm{12-x}}$M$_{\mathrm{x}}$Sb$_{4}$S$_{13})$, where M is transition metal such as Zn or Fe, will have low lattice thermal conductivity and good electronic transport properties. We have experimentally investigated the relationship between ZT and x content of different transition metals in synthetic tetrahedrites. We have found that the maximum of ZT value is not sensitive to the value of x but is related to valence band hole filling fraction; high ZT can be maintained over a large range of x. The compositions studied span the range of those of natural mineral tetrahedrite. To demonstrate that the natural mineral itself can be used as a source material, we synthesized samples by mixing natural mineral with synthetic Cu$_{12}$Sb$_{4}$S$_{13}$ by balling milling and hot pressing. The resulting samples were single phase with hole filling fraction in the optimum range and displayed maximum ZT values of unity at 723K. This new synthesis method can directly use natural mineral to produce TE materials in large quantities with little effort. [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N12.00003: First-Principles Studies of Earth-Abundant Tetrahedrite Thermoelectrics Yi Xia, Fei Zhou, Vidvuds Ozolins Recent experiments have shown inexpensive and naturally occuring tetrahedrite-based materials that exhibit a thermoelectric figure of merit near unity. These compounds are typically of the form Cu$_{12-x}$M$_{x}$Sb$_{4}$S$_{13}$, where M is a transition metal, such as Zn or Fe, for a wide range of x. Using density-functional theory calculations, the ternary phase diagram and various defect formation energies are calculated. Furthermore, the electronic structure, phonon spectrum and thermoelectric properties are investigated. We observe metallic behavior and strong lattice anharmonicity of stoichiometric Cu$_{12}$Sb$_{4}$S$_{13}$. In addition, doping with transitional metals Zn or Fe increases both resistivity and anharmonicity. The theoretical calculations are in good agreement with experimental measurements. [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:27PM |
N12.00004: Configuring pnicogen rings in skutterudites for low phonon conductivity Invited Speaker: Ctirad Uher During the past dozen or so years, skutterudites have attracted much interest as prospective thermoelectric materials for power-generation applications in the temperature range 500K - 850K. Primary interest was focused on filled forms of skutterudites where loosely-bonded filler species resonantly scatter normal phonon modes of the structure thus reducing the lattice thermal conductivity. Using this approach with multiple fillers and incorporating various forms of nanoinclusions, impressive figures of merit ZT = 1.5-1.7 have been reported with n-type filled skutterudites. Since the dominant heat-carrying modes in skutterudites are associated with vibrations of the pnicogen rings, disruptions of the ring structure by substitutional alloying should be a similarly effective approach of lowering the lattice thermal conductivity. In this talk I discuss our recent work exploring alloying configurations of pnicogen rings that yield particularly low values of the thermal conductivity. We found that compensated double-substitution (replacing two Sb atoms with one atom each from the column IV and column VI elements) is a very effective approach. Our ab initio calculations, in combination with a cluster expansion, have allowed us to identify stable alloy configurations on the Sb rings. Subsequent molecular and lattice dynamics simulations on low energy configurations established the range of atomic displacement parameters and values of the thermal conductivity. Theoretical results turned out to be in good agreement with our experimental thermal conductivity values. Combining both approaches of compensated double-substitution and filling of structural cages should be an effective way of further improving the thermoelectric figure of merit of skutterudites. [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N12.00005: Vibrational dynamics of filled skutterudites $M_{1-x}$Fe$_4$Sb$_{12}$ ($M$ = Ca, Sr, Ba, and Yb) Andreas Leithe-Jasper, Michael Marek Koza, Hannu Mutka, Walter Schnelle, Helge Rosner, Yuri Grin First-principles density-functional theory and lattice-dynamics calculations were performed to study the vibrational dynamics and related observables of the ternary compounds $M_{1-x}$Fe$_4$Sb$_{12}$ ($A$ = Ca, Sr, Ba, Yb). The calculation results are supported by experimental data, which were obtained from neutron inelastic scattering, neutron-diffraction, and heat-capacity measurements. Within the calculation approach based on the theory of harmonic solids all observables are linked to the phonon density of states $Z(\omega)$. The good agreement with experimental data shows that the vibrational dynamics of the ternary skutterudite structures can be described by a set of normal modes. Features in the experimentally obtained density of states $G(\omega)$ reflecting the variation in properties (mass, ionic radius) of the cations Ca, Sr, Ba, and Yb are reproduced by the calculations. [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N12.00006: Cr and Ru substituted defect manganese silicides MnSi$_{\delta }$ ($\delta \sim$ 1.72-1.74) as low thermal conductivity thermoelectrics* Vijayabarathi Ponnambalam, Donald T. Morelli Defect manganese silicides MnSi$_{\delta }$ ($\delta \sim$ 1.72-1.74) belong to a large family of compounds known as Nowotny chimney-ladder (NCL) phases and are closely related to an orthorhombic NCL compound TiSi$_{2}$. One interesting feature is the low lattice thermal conductivity ($\kappa_{L} \sim$ 2.5 W/m K) which may be due to several reasons:$_{\, }$ Since $\delta $ doesn't exceed 1.75 in MnSi$_{\delta }$, a considerable concentration of random vacancies exists on the Si-sublattice and can give rise to a low thermal conductivity. In addition, as synthesized MnSi$_{\delta }$ is a mixture of many phases including Mn$_{4}$Si$_{7}$, Mn$_{11}$Si$_{19}$, Mn$_{15}$Si$_{26}$ and Mn$_{27}$Si$_{47}$ and in all these phases, while a-lattice parameter is closely matched, the c-lattice parameter substantially varies with $\delta $. Such a closely matched a-lattice parameter can cause lattice strain and potentially reduce $\kappa_{L}$. Ru$_{2}$Si$_{3}$ forms solid solutions and Cr can be substituted as much as 20{\%} in MnSi$_{\delta }$. These substitutions can favorably modify the lattice strain and reduce the thermal conductivity further. Hence manganese silicides substituted with small amounts of Cr and Ru have been synthesized. Thermoelectric properties including resistivity, Seebeck and Hall coefficients and thermal conductivity will be studied and presented. *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 20, 2013 12:51PM - 1:03PM |
N12.00007: P-type electronic and thermal transport properties of Mg$_{2}$Sn$_{1-x}$Si$_{x}$ Sunphil Kim, Bartlomiej Wiendlocha, Joseph P. Heremans P-type Mg$_{2}$Sn doped with various acceptors$^{(1)}$$^{(2)}$ has been studied as a potential thermoelectric material. Because of its narrow band gap and high lattice thermal conductivity, the zT values of the binary compound are limited: zT$_{max}$ reported is 0.3$^{(3)}$. In this work, we synthesize and characterize p-type-doped Mg$_{2}$Sn$_{1-x}$Si$_{x}$ with various acceptors. Silicon is added in order to widen the band gap and scatter the phonons. The conduction band degeneracy that yields excellent zT in n-type material in the Mg$_{2}$Sn$_{1-x}$Si$_{x}$ alloy system unfortunately does not apply to p-type material. Thermomagnetic and galvanomagnetic properties (electrical resistivity, Seebeck, Hall, and Nernst coefficients) are measured, along with thermal conductivity and band gap measurements. Finally, zT values are reported. (1) H. Y. Chen et al. Journal of Electronic Materials, Vol. 38, No. 7, 2009 (2) S. Choi et al. Journal of Electronic Materials, Vol. 41, No. 6, 2012 (3) H. Y. Chen et al. Phys. Status Solidi A 207, No. 11, 2523-2531 (2010) [Preview Abstract] |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N12.00008: Electronic and thermoelectric properties of CoSbS and FeSbS David Parker, Andrew F. May, Hsin Wang, Michael A. McGuire, Brian C. Sales, David J. Singh We present a combined theoretical and experimental study of the potential thermoelectric performance of three transition metal antimonide sulfides, CoSbS, FeSbS and NiSbS. From theory we find that NiSbS is metallic and hence of little interest regarding thermoelectric performance. CoSbS and FeSbS are both semiconductors with rather heavy valence and conduction bands, whose thermopower can exceed 200 $\mu$V/K at temperatures of 900 K and carrier concentrations of 10$^{21}$cm$^{-3}$, which is similar to the $n$-type high performance thermoelectric filled skutterudites. The experimental results on several non-optimized $n$-type CoSbS samples confirm its semiconducting nature and indicate a potential for good high temperature thermoelectric performance, finding a ZT for two of the samples of 0.35 at 773 K. Substantially higher ZT values may be possible if the lattice thermal conductivity can be reduced by alloying and the effects of extrinsic scattering, which appear to be substantial in the experimental results, are reduced. [Preview Abstract] |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N12.00009: Doping studies of alkali-metal rocksalt based I-V-VI$_2$ compounds with intrinsically minimal thermal conductivity Michele Nielsen, Vidvuds Ozolins, Joseph Heremans Past research has shown that rocksalt-based I-V-VI compounds have intrinsically low thermal conductivity as a result of the lone-pair electrons on the group V element. Theoretical calculations have revealed the presence marginally stable acoustic phonons which have extremely large Gr\"{u}neisen parameters. These result in a strong anharmonicity in heat-carrying acoustic phonon branches of select I-V-VI$_{2}$ compounds. Here, we extend this work to the electronic properties of the materials, which all have similar valence band structures. As a result of these two material properties, we are able to explore if the excellent zT observed in AgSbTe$_{2}$ extends to materials with cheaper starting elements and better high-temperature stability. Here we introduce new doping studies in I-V-VI$_{2}$ compounds where the group I element is an alkali-metal atom. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N12.00010: Role of Chemical Doping in Enhancement of Thermoelectric Properties of Ca$_{3}$Co$_{4}$O$_{9}$ Jianming Bai, Tao Wu, Trevor A. Tyson, Haiyan Chen, Kaumudi Pandya, Cherno Jaye, Daniel Fischer Single-phase [Ca$_{2}$CoO$_{3}$][CoO$_{2}$]$_{1.61}$ (Ca$_{3}$Co$_{4}$O$_{9})$ materials doped by transition metals were prepared by solid state reaction followed by annealing under oxygen. The temperature dependent thermoelectric properties, including resistivity ($\rho$), Seebeck coefficient (S) and thermal conductivity ($\kappa )$, were measured. In order to understand the origin of the changes in ZT with doping, local (XAS) and long range (XRD) structural measurements as a function of doping were conducted. The electronic properties were probed by x-ray spectroscopic methods. Identification of the locations of the dopant sites and the impact on ZT will be discussed. This work is supported by DOE Grant DE-FG02-07ER46402. The Physical Properties Measurements System was acquired under NSF MRI Grant DMR-0923032 (ARRA award). [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N12.00011: Thermoelectric Performance of Hole-Doped Cu$_2$O Xin Chen, David Parker, Mao-Hua Du, David J. Singh We present an analysis of the thermopower and related properties of hole-doped Cu$_2$O using first-principles calculations and Boltzmann transport theory. Our results show that hole-doped Cu$_2$O has a high thermopower of above 200 $\mu$V/K with doping levels as high as 5.5 $\times$ 10$^{20}$ cm$^{-3}$ at 500 K, mainly attributed to the heavy valence bands of Cu$_2$O. The current theory suggests that hole-doped Cu$_2$O could be a good thermoelectric material. Future experiments are thus suggested to explore its thermoelectric potential for practical use in cooling and power generation applications. [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N12.00012: The Seebeck Coefficient in Oxygen Enriched La$_2$NiO$_4$ Paul Bach, Victor Leboran, Francisco Rivadulla Oxide-based devices show promise for themoelectric applications due to their chemical stability and straightforward fabrication. The La$_2$NiO$_{4+\delta}$ system has been predicted to show an increased thermopower coupled with an increased electrical conductivity around $\delta=0.05$ [Pardo et al. PRB 86, 165114 (2012)] that could lead to a large thermoelectric figure of merit (ZT). We investigate the suitability of lanthanum nickelate as a candidate material for high-ZT devices through a systematic study of oxygenated thin films grown by pulsed laser deposition. We report the electrical conductivity, Seebeck coefficient, and structural morphology of La$_2$NiO$_4$ grown in a range of oxidizing atmospheres and discuss their implications for controlled engineering of thermoelectric properties. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovaci\'on (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N12.00013: Spin-entropy origin and scaling behaviour of thermopower in LaBaCoO system Dewei Zhang, Huaihong Guo, Teng Yang, Zhihe Wang, Zhidong Zhang, Youwei Du We report a detailed investigation of thermopower and magnetic properties for La$_{1-x}$Ba$_x$CoO$_3$. A large negative magnetothempower is found to scale with both magnetic field and temperature, indicating that a spin entropy contribution to thermompower. We have formulated a new and general expression to describe the thermopower from spin entropy with spin-interaction considered. Our formula can fit the scaling behavior quite well and provides a satisfactory description to the observed data. The magnetic results further consolidate our claim. This investigation suggests that spin entropy plays a substantial role in the enhanced thermopower in this cobaltite system. [Preview Abstract] |
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