Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X47: Thermoelectrics -- First-principles SimulationFocus
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Sponsoring Units: DMP Chair: Keivan Esfarjani, University of Virginia Room: BCEC 213 |
Friday, March 8, 2019 8:00AM - 8:12AM |
X47.00001: First-principles Review of Thermoelectric Properties of CuFeS2 and the Effect of Nanostructuring Junsoo Park, Yi Xia, Vidvuds Ozolins Composed of inexpensive and naturally abundant elements, the chalcopyrite mineral CuFeS2 has received attention as a potentially useful thermoelectric. We show that first-principles density-functional theory calculations of thermoelectric properties of n-doped CuFeS2 can successfully reproduce experimental measurements, including the Seebeck coefficient. High values of the Seebeck coefficient are attributed to the strong energy-dependence of group velocities in multiple heavy-effective-mass electronic pockets near the conduction band edge. However, flat band dispersion also leads to low mobility, which forces one to rely on high carrier concentration to achieve high conductivity. This decreases the optimal Seebeck coefficient and limits the achievable power factor. Our calculations predict that ideally doped and nanostructured (to grain size of 20 nm) CuFeS2 can increase zT approximately 5-fold relative to the bulk due to significant reductions in the lattice thermal conductivity, attaining zT = 0.25-0.8 at T=300-700 K. |
Friday, March 8, 2019 8:12AM - 8:24AM |
X47.00002: Structural and electronic properties of ferroelectric domain walls in GeTe from first principles Djordje Dangic, Éamonn Murray, Stephen B Fahy, Ivana Savic Domain walls in ferroelectric oxides can have significantly different properties than their bulk counterparts [1]. This represents a new avenue for the manipulation of material properties for specific purposes. GeTe is a ferroelectric material that is also one of the best performing thermoelectrics, combining beneficial electronic properties with low lattice thermal conductivity [2] and mechanical stability [3]. In this work, we have performed first principles calculations to understand how domain walls affect structural and electronic properties of GeTe. We have identified five different types of domain walls. We find that strong strain-order parameter coupling is present at all of them, which is beneficial for the lattice thermal conductivity reduction. We also show that some of the domain walls are conducting along their planes and insulating out-of-plane. The n- and p-type conduction of these domain walls, discovered in our calculations, presents an opportunity for tuning the electronic transport properties of GeTe for thermoelectric applications. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X47.00003: Investigation of the structural, electronic and thermoelectric properties of GeX (X=S, Se, Te) monochalcogenides Aida Sheibani, Raad Haleoot, Bothina Hamad Electronic band structure calculations were performed using density functional theory (DFT) for the orthorhombic structure of GeS and GeSe compounds, and the trigonal structure of GeTe. These compounds exhibit a semiconductor behavior with band gaps of 1.23, 0.899, and 0.68 eV for GeS, GeSe and GeTe, respectively. Based on these DFT calculations their thermoelectric properties were obtained using Boltzmann transport theory. Different procedures were adopted to increase the thermoelectric properties of these compounds including doping and lowering the dimensionality. |
Friday, March 8, 2019 8:36AM - 8:48AM |
X47.00004: First-principles Study of Phonon Drag Effect in SiGe Alloys Qian Xu, Jiawei Zhou, Te-Huan Liu, Gang Chen Phonon drag is the effect that Seebeck coefficients of semiconductors are often greatly augmented at low temperatures. Recent works have shown that it is important in many materials’ thermoelectric (TE) performance even at room temperature, and the major phonons contributing to phonon drag are with longer mean free path (MFP) and lower frequency than those carrying heat. Meanwhile, the point defects in alloys tend to scatter phonons with short MFP and high frequency. Combining phonon drag with alloying might lead to better low-temperature TE materials. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X47.00005: Thermoelectric properties of ternary chalcogenides and oxides from first principles calculations Hitoshi Mori, Masayuki Ochi, Hidetomo Usui, Kazuhiko Kuroki Several ternary chalcogenide compounds have been reported as high-performance or promising thermoelectric materials. Previous works have shown that AgBiSe2 and TlSbTe2 have high ZT values of 1.5 and 0.87, respectively [1,2]. Even though there are many other possible candidates of ternary chalcogenides, thermoelectric properties of most of them have not been reported. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X47.00006: Lone-pair Driven Thermoelectrics at Room Temperature Saikat Mukhopadhyay, Thomas Reinecke Identifying materials which offer crystal-like charge transport and glass-like phonon transport for improved efficiency (ZT) of thermoelectric materials has been a challenging task. The complex interrelationship between these competing materials properties makes such materials rare. Here we report a series of new materials with promising thermoelectric properties; ZT ~ 0.8, at room temperature. This superior ZT stems from the high electrical conductivity and ultralow thermal conductivity; k ~ 0.3 W/m-K, as obtained from the two-channel model (phonons + oscillators). The calculated k is mainly dominated by the Einstein oscillators, which is similar to the cases with amorphous materials where mean free paths become comparable with the characteristics atomic bond lengths. Very low-group velocities due to weakly bonded atoms and strong anharmonicity associated with S2 lone-pair electrons explain such low-k in these systems. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X47.00007: A search for good semi-metallic thermoelectric materials Mona Zebarjadi, Maxime Markov, Seyed Emad Rezaei, Safoura Nayeb Sadeghi, Keivan Esfarjani Heavily doped semiconductors are the most studied class of thermoelectric materials. The presence of the bandgap breaks the symmetry between electrons and holes, allowing large Seebeck coefficient values which are 2-3 orders of magnitude higher than metals. However, the optimal chemical potential in these materials requires a high level of doping usually larger than 1019 cm-3, resulting in low carrier mobility. Semimetals have properties in between semiconductors and metals with Seebeck coefficient values in between. Since there is no bandgap, the Seebeck coefficient values are small for structures where in electron-hole bands are similar. For example, for Dirac semimetals and at the Dirac point, the Seebeck coefficient is zero. However, if there is a large asymmetry between electron-hole bands (that is there is a large effective mass difference), then the Seebeck coefficient of intrinsic semimetals can be as large as those of heavily doped semiconductors. This combined with large intrinsic carrier mobility, makes semimetals potential thermoelectric candidates. In this talk, I will present our search results for semimetals with large Seebeck coefficient values using first principles calculations. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X47.00008: Temperature effects on the thermoelectric properties of PbTe: a first-principles study Jiang Cao, Jose Querales-Flores, Aoife R. Murphy, Stephen B Fahy, Ivana Savic Thermoelectric materials are of intense interest for energy harvesting applications, because they convert waste heat into electricity. PbTe is one of the most efficient thermoelectric materials. It has a direct narrow gap that increases strongly with temperature [1]. Here we study how the temperature dependence of the electronic bands influences the thermoelectric transport properties of PbTe from first principles. The calculated temperature variation of the direct gap accounts for both thermal expansion and electron-phonon coupling [2]. The temperature dependence of the electronic bands is modeled using a two band Kane model. We also build accurate models of phonon bands and electron-phonon scattering from first principles [3]. By solving the Boltzmann equation, we calculate the thermoelectric transport properties of PbTe in very good agreement with experiments. We find that the temperature variation of the direct gap has substantial effects on these properties, leading to a high figure of merit zT over a broader range of doping concentrations at high temperatures. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X47.00009: Electrical and thermal properties of 2D semimetallic transition metal dichalcogenides TiSe2 and ZrTe2 Seyed Emad Rezaei, Safoura Nayebsadeghi, Mona Zebarjadi, Keivan Esfarjani 2D materials have manifested a variety of interesting electrical and thermal properties. In this work, we have investigated the electrical and thermal properties of semi-metallic TiSe2 and ZrTe2 using density functional theory calculations. The effect of several exchange-correlation potentials on the band structure and thermoelectric properties has been investigated. We have also shown that tensile strain will open a gap and cause a corresponding non-linear change in electrical transport properties of these materials. Finally phonons and thermal conductivity of ZrTe2 were calculated, and its thermoelectric properties assessed. |
Friday, March 8, 2019 9:48AM - 10:24AM |
X47.00010: Thermal Transport of Part-crystalline Part-liquid Materials Invited Speaker: Wenqing Zhang Multi-component materials usually manifest crystal structure with chemical bond hierarchy, exhibiting the part-crystalline part-liquid (PCPL) or part-crystalline part-amorphous state as the emerging candidates of thermoelectric materials. These materials contain at least two different types of sublattices, one crystalline and another one strongly disordered or liquid-like, leading to extremely low lattice thermal conductivity. This talk presents a survey on the general characteristics of the thermal transport in the part-crystalline materials. We also develop an approach to simulate the complex thermal transport process. We also compare the results in Green-Kubo method and Boltzmann transport theory to elucidate the thermal conductivity of PCPL materials by using empirical interatomic potentials fitting to the liquid-like thermoelectrics like Cu2Se. The contribution to thermal transport from each structural component, i.e. the rigid-crystalline, strongly disordered, and/or liquid-like parts, are respectively analyzed, and the underlying mechanism is elucitated. Based on the observation, a general trend about the thermal transport in a large group of materials is analyzed. Relationship to minimum thermal conductivity is also discussed. |
Friday, March 8, 2019 10:24AM - 10:36AM |
X47.00011: Abstract Withdrawn
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Friday, March 8, 2019 10:36AM - 10:48AM |
X47.00012: First principles study on the thermoelectric properties of delafossite compounds Hidetomo Usui, Kazuhiko Kuroki Thermoelectric materials should have the coexistence of large power factor PF = σS2 and low thermal conductivity for the enhancement of thermoelectric efficiency. It is however difficult to obtain good thermoelectric materials because the power factor is maximized at a certain doping level due to the relationship between the Seebeck coefficient and the electrical conductivity. We proposed that the ``pudding mold type band”, which has a flat portion at a band edge gives rise to large power factor [1,2]. |
Friday, March 8, 2019 10:48AM - 11:00AM |
X47.00013: First-principles study of LaOBiPbS3 and its analogous compounds as thermoelectric materials Keiya Kurematsu, Masayuki Ochi, Hidetomo Usui, Kazuhiko Kuroki LaOBiPbS3 is a kind of pnictgen-dichalcogenide layered compounds, which have recently been investigated as thermoelectric materials owing to their low thermal conductivity and high controllability of constituent elements [1, 2]. However, thermoelectric performance of LaOBiPbS3 is not very high and that of its analogous compounds is still unknown. In this study, we theoretically investigate the thermoelectric property of LaOBiPbS3 and its analogous compounds : LaOPnTtCh3 (Pn = As, Sb, Bi; Tt = Sn, Pb; Ch = S, Se). We find that there are two key factors for increasing thermoelectric performance: one is the spin-orbit coupling, mainly controlled by Pn, and the other is the hybridization between Pn in the PnS2 layer and Ch in the rock-salt layer, which determines the gap size. In fact, we find that LaOSbPbSe3, which optimizes these key factors but has not been synthesized yet, can have a power factor that is about 5 times as large as that of the known compound LaOBiPbS3. |
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