Resistivity and Thermal Expansion (4.2–820 K) of Skutterudites after Severe Plastic Deformation via HPT

Abstract

Thermoelectric materials with a high figure of merit, ZT, are the essential basis to build thermoelectric generators, which can directly convert heat into electricity. Severe plastic deformation (SPD) via high‐pressure torsion (HPT) was successfully applied to enhance ZT of ball‐milled and hot‐pressed skutterudites as well as to produce bulk nanostructured skutterudites directly from powders. SPD introduces many defects into the sample and in parallel the crystallite size is significantly reduced. During measurement‐induced heating these defects anneal partially out, and the grains grow. In this work for the first time systematically the changes of the temperature‐dependent electrical resistivity and of thermal expansion were compared. It could be shown that for p‐ and n‐type skutterudites, being hot‐pressed and HPT‐processed as well as directly HPT‐processed from compacted powder, these changes occur more or less simultaneously within the same temperature ranges. This evaluation gives a much deeper insight into the thermoelectric behavior of HPT samples under the influence of changing temperature.