Fracture mode, microstructure and temperature-dependent elastic moduli for thermoelectric composites of PbTe–PbS with SiC nanoparticle additions

Abstract

Twenty-six (Pb_0.95Sn_0.05Te)_0.92(PbS)_0.08–0.055% PbI₂–SiC nanoparticle (SiC_np) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiC_np additions (1–3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.

Keywords:

• elastic properties
• porosity
• thermoelectric
• nanocomposites

Acknowledgements

The authors acknowledge the financial support of Office of Naval Research Grant N00014-08-1-0613. The authors also acknowledge the Department of Energy, “Revolutionary Materials for Solid State Energy Conversion Center,” an Energy Frontiers Research Center funded by the US Department of Energy, Office of Science, Office of Basic energy Sciences under award number DE-SC0001054 for financial support of Robert Schmidt for the powder processing done in this study as well as support of Jennifer Ni, Edgar Lara-Curzio and Eldon Case for the data analysis and paper preparation stage of this research. Research through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program was sponsored by the U S Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Edward Timm and Karl Dersch, Michigan State University, assisted the authors with hot pressing, PECS and specimen cutting. The Center for Statistical Training and Consulting at Michigan State University provided advice on the error analysis in this study.