Anomalous Thermoelectric Transport Phenomena from Interband Electron-Phonon Scattering

The Seebeck coefficient and electrical conductivity are two central quantities to be optimized simultaneously in designing thermoelectric materials, and they are determined by the dynamics of carrier scattering [1]. We uncover a new regime where the presence of multiple electron bands with different effective masses, crossing near the Fermi level, leads to strongly energy-dependent carrier lifetimes due to intrinsic electron-phonon scattering. In this anomalous regime, electrical conductivity decreases with carrier concentration, Seebeck coefficient reverses sign even at high doping, and power factor exhibits an unusual second peak [2]. We explain the origin and magnitude of this effect using a general simplified model as well as first-principles Boltzmann transport calculations in recently discovered half-Heusler alloys. We identify general design rules for using this paradigm to engineer enhanced performance in thermoelectric materials. We performed detailed first-principles electron-phonon transport calculations for several candidate materials to investigate the potential for increased thermoelectric performance based on this light-heavy band mechanism.<br/>[1] B. Kozinsky, D. J. Singh, <i>“</i><i>Thermoelectrics by Computational Design: Progress and Opportunities”</i>, Annual Reviews of Materials Research, 51, 565 (2021)<br/>[2] N. Fedorova, A. Cepellotti, B. Kozinsky, <i>“Anomalous thermoelectric transport phenomena from interband electron-phonon scattering”</i>, Adv. Func. Mater., 32, 2111354 (2022)