Stability and effect of PbS nanoinclusions in thermoelectric PbTe

Abstract

In recent years hierarchical thermoelectric materials have been engineered to reach record breaking thermoelectric figures-of-merit (zT) making them attractive in green transition energy conversion applications. PbTe constitutes an archetypical example, where PbS nanoinclusions presumably scatter phonons, while leaving the electrical properties intact. For widespread use of such materials, their structural integrity and chemical stability are equally important to the thermoelectric performance. Here, we show by operando X-ray diffraction and physical property measurements that PbS nanoinclusions in PbTe are not stable at operating conditions. The PbS nanoinclusions grow in size, but surprisingly this does not diminish the thermoelectric performance. Comparison with samples without nanostructures reveals that the PbS inclusions primarily affect the electrical properties at elevated temperatures, and to a lesser degree the lattice thermal conductivity. Nanostructured materials have significantly moved thermoelectric performance limits, but if we are to develop materials by design rather than trial-and-error, it is important that the nature, effect and stability of nanoinclusions are characterized under operating conditions.