Influence of Ni impurities on the thermoelectric properties of Ca-partially filled skutterudites CaxCo4Sb12

Polycrystalline samples of the skutterudite compounds CaxCo4Sb12 were synthesized and investigated by means of electrical resistivity, thermal conductivity, and thermopower in the 300-800K temperature range. Additional Hall effect measurements were performed between 2 and 300 K. Both Ni-free and Ni-containing Co powders were used as starting materials to elucidate the impact of Ni impurities at the ppm level on the thermoelectric properties. The presence of minute amounts of Ni atoms in the crystal structure leads to enhanced thermopower values with respect to the Ni-free samples, likely associated with the development of additional electron pockets near the Fermi level. Ni impurities, thus, play a significant role on the transport properties and lead to a spectacular increase in the dimensionless thermoelectric figure of merit ZT of up to 150% at 800 K. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768439]