Interplay of Electronic and Lattice Degrees of Freedom in Thermoelectric Materials
David J. Singh
Department of Physics and Astronomy
University of Missouri
Abstract: Thermoelectric materials are important for spacecraft power, waste heat recovery, thermal management and cooling applications. The efficiency of thermoelectric systems is limited by materials performance. This is measured by the figure of merit ZT=sS2T/k, where S is the thermopower and the other symbols have their usual meaning. ZT is therefore a composite property involving electronic and thermal transport, with high ZT favored by high conductivity, high thermopower and low thermal conductivity. However, these properties are inter-related, often to the detriment of high ZT. This talk discusses these correlations, and points out one positive correlation and ways to exploit it. This is the correlation between lattice thermal conductivity and mobility that occurs in materials near polar instabilities. PbTe and GeTe are examples of materials in this category. This proximity to polar distortions is associated with strong anharmonicity of the phonons and also lattice contributions to the dielectric constant. High dielectric constant in turn favors screening of ionized impurity scattering and high carrier mobility. The chemical basis for these effects in terms of electronic structure is discussed along with directions for using this to discover new thermoelectric systems. We also discuss ways of overcoming the contradictions inherent in high ZT and approaches that can be used to identify favorable compositions in relation to overcoming these contradictions.
Introduction: David J. Singh is a Curators’ Professor in Physics and Astronomy at the University of Missouri, where he has been since 2015. Previously, he was a Corporate Fellow at Oak Ridge National Laboratory, and before that head of the Theory of Functional Materials Section at the U.S. Naval Research Laboratory. He is a graduate of the University of Ottawa, where he received a Ph.D. degree in Physics in 1985. He is a leading expert on methods for first principles calculations and their application to thermoelectric, superconducting, ferroelectric and other classes of materials. He is an originator of the sign changing s-wave model for Fe-based superconductors, and a developer of the BoltzTraP code for thermoelectrics. He was the recipient of the E.O. Hulbert Science Award and the Gordon Battelle Prize. He is a Fellow of the American Physical Society and of the Royal Society of Chemistry. Singh is the author of more than 580 refereed scientific publications, which according to ISI have received in aggregate more than 42,000 citations with an h-index of 73.
Venue: Room 201 of Basic Energy Science Building
Time:30th May, 2019, 14:00 pm