First-principles study of intra- and inter-valley scattering in thermoelectric materials

A major goal of thermoelectric (TE) research is to develop materials with improved efficiencies. One strategy towards higher-performance TEs is band convergence, which seeks to align multiple electronic valleys within a narrow energy range. Theoretical modeling indicates that band convergence can lead to enhanced inter-valley scattering, which can reduce, or potentially offset, the benefits of this strategy. To help understand what controls the strength of inter-valley collisions, and their impact on TE properties, in this talk we present a density functional theory (DFT) study to characterize intra- and inter-valley electron-phonon scattering in six materials: three lead chalcogenides (PbS, PbSe, PbTe) and three half-Heuslers (ScNiBi, ScPbSb, ZrNiSn). The intra- and inter-valley scattering rates are analyzed by separating the contributions originating from the electron dispersion and from the electron-phonon coupling, to help elucidate the underlying factors that govern the scattering characteristics. We also propose a simple approach to estimate the inter-valley coupling strength, which is found to agree qualitatively with the rigorous results. These findings help guide our search of new and improved high-performance TEs.