Tailoring Thermoelectric Transport Properties of Ag-Alloyed PbTe: Effects of Microstructure Evolution.

Capturing and converting waste heat into electrical power through thermoelectric generators based on the Seebeck effect is a promising alternative energy source. Among thermoelectric compounds, PbTe can be alloyed and form precipitates by aging at elevated temperatures, thus reducing thermal conductivity by phonon scattering. Here, PbTe is alloyed with Ag to form Ag-rich precipitates having a number density controlled by heat treatments. We employ complementary scanning transmission electron microscopy and atom probe tomography to analyze the precipitate number density and the PbTe-matrix composition. We measure the temperature-dependent transport coefficients and correlate them with the microstructure. The thermal and electrical conductivities, as well as the Seebeck coefficients, are found to be highly sensitive to the microstructure and its temporal evolution, e.g., the number density of Ag-rich precipitates increases by ca. 3 orders of magnitude and reaches (1.68 ± 0.92) × 1024 m-3 upon aging at 380 °C for 6 h, which is pronounced by reduction in thermal conductivity to a value as low as 0.85 W m-1 K-1 at 300 °C. Our findings will help to guide predictive tools for further design of materials for energy harvesting.