Tuning of mechanical properties of doped PbTe-based thermoelectric materials driven by intrinsic defects

Abstract

One of the primary factors that significantly restricts the lifetime of thermoelectric devices based on PbTe is the high brittleness of doped PbTe. There are several types of defects that are commonly observed in PbTe, which can have either a positive or negative impact. These include the substitution of Pb or Te by other atomic species to achieve n- or p-type doping, the substitution of Pb with Te (Te-rich PbTe) and vice versa (Pb-rich PbTe), and also Pb or Te vacancies. Experimentally, it is challenging to determine the influence of each defect on the mechanical properties at the atomic level. The focus of this study is the chemical bonding in the PbTe crystal, with substitutions of Pb by Bi (n-type) and Na (p-type), as well as Ag/Cu interstitials. Intrinsic defects are also examined, involving substitutions of Pb by Te and vice versa, and vacancies of Pb or Te. In order to achieve this, calculations of the elastic tensor are performed, as well as Crystal Orbital Hamilton Population (COHP) analysis, in combination with large-scale simulations of tensile deformation using deep neural network (DNN) interatomic potentials. The findings of this study provide insight into how to precisely change mechanical properties through defect formation. The results of this advanced comprehensive study can facilitate the development of high-efficiency thermoelectric generators based on PbTe.