Transport Properties of Sn-doped CoSb3 Skutterudites

Sn-doped CoSb3 (CoSb3-ySny) skutterudites were prepared by hot pressing, and their doping effects on the thermoelectric and the electronic transport properties were examined. A single-phase delta-Co(Sb,Sn)(3) was obtained, but it decomposed to gamma-Co(Sb,Sn)(2) for y >= 0.3, which means that the solubility limit of Sn in Sb is y <0.3. The Hall and the Seebeck coefficients confirmed that all the Sn-doped CoSb3 samples exhibited p-type conductivity. The carrier concentration increased with increasing doping content. However, the carrier mobility decreased with increasing doping content because the hole mean free path was reduced by ionized impurity scattering. The Seebeck coefficient and the electrical resistivity decreased and then were almost independent of the carrier concentration because the increase in the carrier concentration caused by doping was competitive with the decrease in the carrier mobility caused by ionized impurity scattering. The thermal conductivity decreased with increasing carrier concentration because Sn acted as phonon scattering centers. The lattice contribution to the total thermal conductivity in the Sn-doped CoSb3 was dominant.