Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q12: Focus Session: Theory of Bulk Thermoelectric Materials |
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Sponsoring Units: DMP GERA FIAP DCOMP Chair: David Singh, Oak Ridge National Laboratory Room: 007C |
Wednesday, March 4, 2015 2:30PM - 2:42PM |
Q12.00001: Thermal transport properties of complex oxides from first principles Aqyan Bhatti, Ankit Jain, Alan McGaughey, Nicole Benedek Thermal transport properties of materials are key parameters in the design of many engineering devices. For this reason, it is highly desirable to be able to control or tailor the thermal properties of materials for specific applications. Complex oxides are attractive in this regard, due to their low and potentially highly tunable thermal conductivity. However, the theoretical description of the thermal transport properties of oxides presents a number of challenges compared to conventional semiconductors. For example, oxides tend to have complex crystal structures and the atoms interact through long-range electrostatic forces. In this talk, we use the example of PbTiO$_3$ to discuss some of the challenges and opportunities associated with thermal transport predictions in complex oxides. For example, many oxides contain very low-lying optical branches, which may provide important acoustic-optical scattering channels. In addition, it is often possible to tune the frequencies of such optical modes with epitaxial strain. We also link the observed negative thermal expansion behavior of PbTiO$_3$ to two zone-boundary modes with large, negative Gr\"{u}neisen parameters and comment on the consequences of this finding for the thermal transport properties of this material. [Preview Abstract] |
Wednesday, March 4, 2015 2:42PM - 2:54PM |
Q12.00002: Ab Initio DFT study of electronic and thermoelectric properties of crystalline Ge2Sb2Te5 Wilfredo Ibarra Hernandez, Jean-Yves Raty Pseudo-binary phase change materials such as (GeTe)n/(Sb2Te3)m have been recently considered for thermoelectric applications. Among these, Ge2Sb2Te5 (GST225, n$=$2 and m$=$1) is very popular as it is the leading candidate for non-volatile memory devices such as phase change random access memory. It is well know that the stable crystal structure of GST225 is hexagonal, with atomic layers stacked in the c direction. The stacking sequence is however still under some debate, and structures varying from conventional semiconductor to Dirac semimetal have been claimed to differ only by the nature of the stacking sequence. Here we present electronic, dynamic and thermoelectric calculations on three different stacking sequences of crystalline GST225. We use ab-initio DFT calculations together with Boltzmann transport equations to access thermoelectric properties within the constant relaxation time approximation. Our results show that all three proposed stacking sequences are (meta-)stable. From the density of states we determine that two structures are metallic while the most stable structure has a 0.35 eV band gap. Above 100K, the computed Seebeck coefficient seems to indicate that the experimentally observed structure is the Dirac semimetal one, the doping level being of the order of 1 $\times$ 1020 cm$^{-3}$. [Preview Abstract] |
Wednesday, March 4, 2015 2:54PM - 3:06PM |
Q12.00003: Electronic and Thermoelectric Properties of Zintl 14-1-11 Compounds Computed with DFT$+$U Trinh Vo, Paul von Allmen, Sabah Bux, Jean-Pierre Fleurial We present results for the electronic structure and thermoelectric properties of zinlt 14-1-11 compounds, in particular~Ca14-yYbyAlSb11-xAsx~(x $=$ 0.11, and y $=$ 0.14) and Yb14MgSb11, using DFT$+$U and Boltzmann's transport equation.~ The effect of selective substitutions at different cation, anion, and central metal sites on the electronic properties is also investigated.~ We found that selective atomic~substitution affects~the electronic structure significantly, leading in certain cases to substantial improvement of the thermoelectric properties. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:42PM |
Q12.00004: Part-crystalline part-liquid state and electrical/thermal transport in materials with chemical-bond hierarchy Invited Speaker: Wenqng Zhang A concept of part-crystalline part-liquid state (or liquid-like), and even part-crystalline part-glass state (or glass-like), was demonstrated in some materials such as Cu3SbSe3 with chemical-bond-hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large amplitude vibrations and even flow of the group of species atoms. The large-amplitude vibrations and movement of atoms can generate unusual severe phonon scattering and thermal damping due to the collective low-frequency vibrations similar to the Boson peak in amorphous or liquid materials. While different phase or state may have large energetic discrepancy, whether the thermally-induced part-crystalline state is undergoing phase transition becomes an interesting issue. In addition, our earlier work reported that second-order phase transition could induce extreme electron and phonon scattering in thermoelectrics. The above work clearly demonstrated that the unusual effect from structural fluctuations on thermal and electrical transport in thermoelectrics should be paid attention to. While materials with these structural changes can retain extremely low lattice thermal conductivity and unusual electron transport and become promising candidates for high-performance thermoelectrics, underlying mechanism is yet to be explored. [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q12.00005: Compressed sensing approach for calculating lattice thermal conductivity of complex thermoelectric compounds Vidvuds Ozolins, Yi Xia, Weston Nielson, Fei Zhou Earth-abundant minerals such as tetrahedrite Cu$_{12}$Sb$_4$S$_{13}$ have recently received attention as promising thermoelectrics due to a combination of a relatively high figure of merit ($ZT > 1$ at $T=700$ K in tetrahedrite), good mechanical properties and inexpensive bulk processing methods. Like many large unit-cell thermoelectrics, these compounds often have complex chemical formulas with very large unit cells that pose challenges to our ability to study their lattice dynamical properties theoretically. Here we show that a recently introduced approach, compressive sensing lattice dynamics (CSLD) [F. Zhou \textit{et al.}, Phys. Rev. Lett. 113, 185501 (2014)] provides an accurate and computationally efficient platform for investigating anharmonic lattice dynamics in complex materials. We will discuss the basic ideas and illustrate the performance of CSLD for the lattice thermal conductivity $\kappa_L$ of tetrahedrite, collusite, pyrite, and other earth-abundant mineral compounds. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q12.00006: A Robust Approach to Lattice Thermal Conductivity Weston Nielson Thermal conductivity is a key parameter in designing high performance thermoelectric materials. A multitude of computational methods have been developed to calculate lattice thermal conductivity. Molecular dynamics (MD) based techniques, including equilibrium and non-equilibrium methods, in addition to non MD-based solutions, such as the Boltzmann Transport Equation (BTE), are all capable of calculating thermal conductivity, but each comes with different sets of limitations and difficulties. After extensive use of these different methods, we have developed a robust set of tools for obtaining high-quality lattice thermal conductivity values of crystalline solids. The crux of our method involves a novel compressive sensing (CS) based approach for efficiently calculating high quality force constants for crystalline materials. The result is a technique for building lattice dynamical models that can treat compounds with large, complex unit cells and strong anharmonicity, including those with harmonically unstable phonon modes. [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q12.00007: Temperature dependent phonon properties of thermoelectric materials Olle Hellman, David Broido, Brent Fultz We present recent developments using the temperature dependent effective potential technique (TDEP) to model thermoelectric materials. We use ab initio molecular dynamics to generate an effective Hamiltonian that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, and heat capacities. Results are presented for (among others) SnSe, Bi$_2$Te$_3$, and Cu$_2$Se proving the necessity of careful modelling of finite temperature properties for strongly anharmonic materials. [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q12.00008: Density functional study of silver defects in telluride thermoelectric materials Byungki Ryu, Min-Wook Oh, Su-Dong Park Silver impurity in telluride thermoelectric materials forms various defect and impurity structures, such as AgSb rich nanoregion in Ag-Sb-Pb-Te, Ag$_{\mathrm{2}}$Te and metallic silver in PbTe. To understand the atomic, electronic, energetic, and diffusion properties of silver impurities in telluride systems, we have performed the density functional theory and density functional perturbation theory calculations of silver doped PbTe. Under Te and Ag rich condition, silver telluride impurity phase or Ag-dimer defects are expected to be easily formed. Under Te poor condition, silver point defects are calculated to be easily formed and they are more stable than native point defects of PbTe, implying that silver point defect might be the major dopant responsible for the carrier generation in PbTe. We also calculated the diffusion coefficient and diffusion length of silver point defect in PbTe. Based on the results, we discussed the electrical and thermoelectric properties of silver doped PbTe. [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q12.00009: Quasiparticle band structures and thermoelectric transport properties of p-type SnSe Guangsha Shi, Emmanouil Kioupakis We used density functional and many-body perturbation theory to calculate the band structure and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients within the constant relaxation time approximation as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at low doping and high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10$^{19}$--10$^{20}$ cm$^{-3}$ range. This work was supported in part by the National Science Foundation (DMR-1254314) and in part by CSTEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Computational resources were provided by the DOE NERSC facility. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q12.00010: Thermoelectric properties of higher manganese silicides Yu-Chih Tseng, Vijay Shankar Venkataraman, Hae-Young Kee Higher manganese silicides (HMS) are promising thermoelectric materials that may be broadly deployable because of the abundance of the constituent elements and their non-toxic nature. We study the thermoelectric properties of HMS using density functional theory calculations and tight-binding models to fit these calculations. We estimate charge carrier density and mobility, and compare with experimental data. Theoretically obtained thermal and electrical conductivities, and the Seebeck coefficients are presented. Possible scattering mechanisms and relations to figure of merit are also discussed. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q12.00011: First-principles Study of Lattice Thermal Conductivity of Cu$_{3}$SbS$_{4}$ and Cu$_{3}$SbSe$_{4}$ Yi Xia, Fei Zhou, Weston Nielson, Vidvuds Ozolins Linearized self-consistent Boltzmann transport equation (BTE), utilizing interatomic force constants (IFCs) obtained via compressive sensing lattice dynamics (CSLD), is used to study the lattice thermal conductivity ($\kappa_{l}$) of Cu$_{3}$SbS$_{4}$, Cu$_{3}$SbSe$_{4}$ and their solid solutions. With these IFCs we obtain bulk lattice thermal conductivity in good agreement with experimental measurements. We also compare Cu$_{3}$SbS$_{4}$ and Cu$_{3}$SbSe$_{4}$ with respect to Gr\"uneisen parameter, group velocity, phonon lifetime, mean free path and cumulative $\kappa_{l}$. All the analysis indicates that (1) slightly larger group velocity and lifetime of acoustic modes found in Cu$_{3}$SbS$_{4}$ lead to larger $\kappa_{l}$ compared with Cu$_{3}$SbSe$_{4}$ over the whole temperature range. Contributions from optical modes to $\kappa_{l}$ for both compounds are about 25\% at temperature higher than 300K. This large portion of $\kappa_{l}$ can not be neglected if one aims to predict accurate $\kappa_{l}$; (2) Nanostructures with length less than 10nm can effectively reduce $\kappa_{l}$ by about 80\% for both of the compounds; (3) solid solution of two compounds can effectively reduce $\kappa_{l}$ as much as 40\% at room temperature. [Preview Abstract] |
Wednesday, March 4, 2015 5:06PM - 5:18PM |
Q12.00012: New insights into thermal conductivity by non-equilibrium molecular dynamics Philip Allen, Yerong Li Non-equilibrium molecular dynamics (NEMD) is often used to simulate thermal conductivity ($\kappa$). A steady state heat current and corresponding temperature gradient are created computationally over a simulation cell of thousands of atoms. We advocate a variation that gives directly $\kappa(q)$, the Fourier transform of the non-local $\kappa(x-x^\prime)$ that relates $J(x)$ to $\nabla T(x^\prime)$. The algorithm is tested on the Lennard-Jones liquid and crystal, and is efficient for extraction of the macroscopic $\kappa={\rm Lim}_{q\rightarrow0}\kappa(q)$. Peierls-Boltzmann theory gives (in relaxation-time approximation) a closed-form expression for $\kappa(q)$ that can be used to study the $q$-dependence in the small $q$ limit, and how it depends on simulation cell dimensions in NEMD. The frequency-dependent relaxation rate $1/\tau_Q \propto \omega_Q^2$ was chosen for detailed comparison with simulation. For an isotropic cell ($N_x=N_y=N_z$), the behavior is $\kappa(q)=\kappa-A*q^{1/2}$. For the more typical anisotropic cell with one length ($N_z$) large compared to the others, there is an additional term $\propto q^{-1/2}/N_xN_y$. This divergent contribution disappears in the bulk limit. Strategies for extrapolation of simulations are suggested. [Preview Abstract] |
Wednesday, March 4, 2015 5:18PM - 5:30PM |
Q12.00013: Strain-induced semi-metal to semiconductor transition and strong enhancement in thermopower of TiS$_{2}$ Atanu Samanta, Tribhuwan Pandey, Abhishek K. Singh Electronic properties of transition-metal dichalcogenides (TMDs) (MX$_{2}$, where M = Mo, W and X = S, Se, Te) are very sensitive to the applied pressure/strain, causing a semiconductor to metal transition. Using first principles density functional theory calculations, we demonstrate that bulk TiS$_{2}$ changes from semi-metal to semi-conducting electronic phase upon application of uniform biaxial strain. This phase transition is responsible for the charge transfer from Ti to S and reduces the overlap between Ti-($d$) and S-($p$) orbitals. The transport calculations show a three-fold enhancement in thermopower for both $p$- and $n$-type TiS$_{2}$ due to opening of band gap along with changes in dispersion of bands. The electrical conductivity and thermopower shows a large anisotropy due to the difference in the effective masses along the in-plane and out-of-plane directions. We further demonstrate that the enhancement of thermoelectric performance, can also be achieved by doping TiS$_{2}$ with larger iso-electronic elements such as Zr or Hf at the Ti sites. [Preview Abstract] |
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