Changes of Thermoelectric Properties and Hardness after HPT Processing of Micro- and Nanostructured Skutterudites

In this paper the influence of the starting material on the physical properties after severe plastic deformation (SPD) will be discussed. A bulk p-type skutterudite DD0.44Fe2.1Co1.9Sb12(DD stands for didymium which consists of 4.76% Pr and 95.24% Nd) was (1) hand milled and hot pressed, resulting in crystallite sizes in the μm range and (2) ball milled and hot-pressed, reducing the crystallite size to about 100nm, and afterwards deformed using high pressure torsion (HPT). It could be shown that in both cases the lattice parameters were slightly higher after HPT processing, the difference of the electrical resistivity values between heating and cooling was much larger for the skutterudite, which stems from the microstructured alloy. The thermopower data for both alloys are slightly higher, resulting in power factors at 800K almost like (originally nanosample) or even higher (originally microsample) than before HPT. As the thermal conductivity is always lower after SPD, a much higher ZT can be expected. After deformation hardness measurements showed a much higher increase for the nanosample compared to that of the microstructured one.