Optimized thermoelectric properties of p-type PbTe0.88Ag0.12 through metallic transition and investigation of its time- and temperature-dependent oxidation process

Abstract

Lead telluride (PbTe) is a well-known thermoelectric material with a figure of merit (zT) typically exceeding 1 at intermediate temperatures. However, due to its intermetallic properties, the oxidation of PbTe introduces oxygen-related defects. These defects not only destabilize the crystal but also reshape the delicate balance between electrical and thermal conductivity. The present work investigates the influence of Ag incorporation on its thermoelectric transport and oxidation behavior. Unconventional p-type silver-doped PbTe (PbTe_1−xAg_x, where x = 0, 0.04, 0.08, 0.12) was synthesized. Structural analysis confirmed the successful incorporation of Ag into the lattice. Density functional theory (DFT) calculations revealed that Ag doping induces a narrow bandgap semiconducting to semi-metallic transition, which potentially enhanced the electrical conductivity. Concurrently, phonon calculations indicated intensified phonon scattering, which contributes to a suppressed lattice thermal conductivity. This synergistic effect of electronic band engineering and phonon suppression proved as a highly effective strategy for enhancing thermoelectric performance. As a result, the thermoelectric figure of merit, zT, improved from 1.06 for pristine PbTe to 1.37 at 753 K for the PbTe_0.88Ag_0.12 composition, representing a 29.2% enhancement. Beyond improving the performance, Ag doping also significantly enhanced the material's operational stability. Comprehensive thermal and structural analyses, supported by time- and temperature-dependent oxidation studies, demonstrated that Ag doping leads to a markedly reduced oxidation rate. This suppression of oxidation effectively stabilizes the material against degradation at both room temperature and intermediate operating temperatures.