Controlling phonon lifetimes via sublattice disordering in AgBiSe2

Abstract

Due to their ability to convert thermal gradients into useful electrical energy, thermoelectrics are promising for energy efficiency uses. Thermoelectric conversion rates are driven by the ratio of electrical to thermal conductivity in the material, thus substantial research focuses on balancing these competing mechanisms. Here the authors use state-of-the-art neutron scattering and computational modeling to investigate the temperature dependence of the crystal structure, phonon dispersions, and phonon lifetimes to provide new microscopic insight to thermal conductivity suppression in AgBiSe2, a thermoelectric exhibiting a cationic sublattice disordering at high temperature. These combined efforts enable the authors to definitively describe contributions to the thermal conductivity arising from a step-like change in phonon scattering rates directly originating from the combined effects of mass and force-constant disorder due to cation disorder at the structural phase transition. This study highlights the potential of tunable microstructures to control phonon scattering rates in real materials, a necessary component for rational material design, particularly for thermoelectrics.