Phonon Scattering and Thermal Transport in PbSe and Medium Entropy Thermoelectric PbSe0.5Te0.25S0.25 with Defects of Different Dimensions

Abstract

<p>Defect engineering has been proven to be effective in optimizing the thermoelectric performance by tailoring the lattice thermal conductivity. Understanding the roles of defects with different dimensions on heat-carrying phonons is crucial. In this study, we investigated the lattice dynamics and thermal transport properties of PbSe and medium entropy PbSe_0.5Te_0.25S_0.25 with different defects, using a machine learning interatomic potential. We find that the introduction of 3% Pb vacancies reduces lattice thermal conductivity (<em>k</em>_<em>L</em>) of PbSe by approximately 40%, similar to dislocations (with a density of 2 × 10¹⁶ m^–2) and nanograins (grain size of 4000 nm³). Vacancies enhance phonon scattering at frequencies above 0.5 THz, whereas dislocations, stacking faults, and grain boundaries primarily hinder phonon propagation below 1.5 THz. In contrast, in PbSe_0.5Te_0.25S_0.25, vacancies have weaker effects on thermal transport suppression due to the intrinsic entropy-induced high-frequency phonon scattering; higher-dimensional defects, such as grain boundaries, stacking faults, and dislocations, are more effective for reducing <em>k</em>_<em>L</em> by enhancing phonon scattering at frequencies lower than 1 THz. This study reveals the mechanisms by which defects influence lattice thermal conductivity and provides valuable guidance for optimizing the thermal transport in entropy engineered systems.<br></p>