Mechanical properties of low-cost, earth-abundant chalcogenide thermoelectric materials, PbSe and PbS, with additions of 0-4 % CdS or ZnS

PbTe-based thermoelectric (TE) materials have been extensively investigated as TE generator materials, however, the tellurium content limits the application potential due to both availability and cost. Replacing the tellurium with selenium or sulfur produces an isomorphic TE material with very good reported figure of merit, ZT, values of 1.3-1.6, but the effect of the material changes designed to increase ZT (doping, nano- and micro-precipitate additions) on mechanical properties has not been reported. In order to effectively incorporate these new materials into TE devices, it is important to understand materials' response to thermally and mechanically imposed loads, which in turn requires knowledge of the mechanical properties. In this study, the hardness was determined by Vickers indentation and elastic modulus and Poisson's ratio were measured using resonant ultrasound spectroscopy on PbSe- and PbS-based TE specimens as a function the addition of 0-4 at.% of CdS or ZnS. With 2.0 or 2.5 at.% Na doping, the hardness of PbSe- or PbS-based TE materials increased by about 30 % and the elastic moduli decreased by 5-10 %. In addition, PbS may be effectively sintered at 723 K when doped with 2.5 at.% Na, but requires a higher sintering temperature when undoped. This study shows that the hardness and moduli of PbSe- or PbS-based TE materials are not strong functions of the addition of CdS or ZnS precipitates.