Low temperature thermoelectric properties of PbTe–CoSb3 composites

A new synthesis route has been applied to the preparation of PbTe–CoSb3 thermoelectric composites (0–8 %wt of PbTe) from nanoparticles of PbTe (6 nm in diameter) synthesized by laser fragmentation of micron-sized particles in water and micron-sized skutterudite CoSb3 powders. The freeze-dried powders have been densified by spark plasma sintering. The morphologies and crystallographic structures have been checked by scanning electron microscopy and x-ray diffraction. The obtained microstructures are quite complex, with more or less agglomeration of the PbTe particles at the grain boundaries of CoSb3. The transport properties (electrical resistivity, thermopower, Hall coefficient, thermal conductivity) of the composites have been investigated in the 2–300 K temperature range and compared to those of the reference CoSb3 material. A change of conduction type has been observed for the composites that became n-type. This change was attributed to substitution of a minute amount of Sb for Te. As could be expected from nanostructuring, lower thermal conductivities are achieved in the composites.