Changes in Physical Properties for HPT-Processed p-Type Skutterudite DD_0.7Fe₃CoSb₁₂

To build thermoelectric generators, which can directly convert heat into electricity, materials with a high figure of merit, ZT are essential. Severe plastic deformation (SPD) via high-pressure torsion (HPT) was successfully applied to produce in a fast and energy saving way bulk nanostructured skutterudites directly from powders. SPD introduces many defects into the sample and in parallel the crystallite size is significantly reduced. HPT-processed DD_0.7Fe₃CoSb₁₂ is a high-quality thermoelectric material with 1.12 &lt; ZT &lt; 1.35 at 750 K. During measurement-induced heating these defects anneal partially out, and the grains grow. It was observed that while heating HPT processed material from room temperature to about 850 K, changes of the temperature-dependent physical properties, most of all the electrical resistivity, the density, and the thermal expansion occur more or less simultaneously around 600 K. For the first time we have combined <i>in situ</i> TEM observations as well as measurements of the elastic modulus and hardness in order to get a deeper insight into the microstructural behavior of a p-type skutterudite, DD_0.7Fe₃CoSb₁₂ (DD = didymium) during increasing temperature from 300 K to 823 K.