Thermoelectric performance of thermally aged nanostructured bulk materials—a case study of lead chalcogenides
© 2020 Elsevier Ltd The performance of nanostructured bulk thermoelectric material is shown to be enhanced because of phonon scattering. However, it is well-known that microstructures evolve by thermal aging, and their stability at the operating temperature is of vital importance to the success of the device. Here, we investigate the effect of long-term annealing (up to 8 weeks) on thermoelectric performance and microstructure of a high-efficiency Na-doped multiphase quaternary Pb chalcogenides. A zT of ~1.7–1.9 in the 700–850 K temperature range is achieved at all stages of thermal aging. A redistribution of Na-dopant between phases above ~630 K is believed to explain an increasing electrical resistivity in aged samples. This is balanced by a reduced total thermal conductivity as thermal aging time increases, possibly because of an increased concentration of nanoscale precipitates in samples aged for 8 weeks. Intermediate annealing of nanostructured lead chalcogenides has been shown to be an effective means of preparing thermally stable, high-performance thermoelectric materials. We have also determined the precipitates coarsening rate constant, k, to be 0.0206 μm/h1/3.