High temperature thermoelectric properties of CoSb3 skutterudites with PbTe inclusions

Nanostructured thermoelectric materials generally exhibit enhanced properties. PbTe-CoSb3 thermoelectric composites (0-8 wt% of PbTe) have been successfully prepared by freeze-drying nanoparticles of PbTe (6 nm in diameter, synthesized by laser fragmentation of micron-sized particles in water) with micron-sized skutterudite CoSb3 powders (similar to 5 mu m in diameter, synthesized by powder metallurgy), followed by spark plasma sintering. X-ray diffraction analyses and scanning electron microscopy observations have been performed. Microstructures reveal an agglomeration of the PbTe particles at the grain boundaries of CoSb3. Electrical resistivity, thermopower, and thermal conductivity measurements have been performed in the 300-800 K temperature range. The composites exhibit n-type conduction whereas the reference CoSb3 skutterudite is p-type. This change of conduction mode is attributed to substitution of Sb for a minute amount of Te in the composites. The influence of both PbTe nanoparticules and Te on the thermoelectric properties is discussed in detail.