Effect of NiSb on the thermoelectric properties of skutterudite CoSb3

Abstract

The phase equilibrium and thermoelectric properties of Co1−xNixSb3 ternary system were examined up to high nickel content x=0.40. NiSb compound with nickel arsenide structure was observed as the impurity phase in the samples with x>0.10 by x-ray diffraction. The sign of the Seebeck coefficient of Co1−xNixSb3 is negative, and the absolute value of the Seebeck coefficient and electrical resistivity generally decreases with increasing x. The thermal conductivity is reduced in the samples with x⩽0.06, but above x=0.06 it increases with increasing x. These behaviors of the thermoelectric properties in the samples with low nickel content are ascribed to the substituted Ni, while those in the samples with high nickel content are ascribed to the precipitated NiSb compound. In order to more reduce the thermal conductivity of the material, we have prepared a sintered CoSb3–NiSb composite where the NiSb particles are dispersed in the CoSb3 matrix by mechanical grinding and hot pressing. The thermal conductivity of the composite is lower than that of the Co1−xNixSb3 system especially at low temperature. The decrease of the thermal conductivity is ascribed to the enhancement of the phonon scattering caused by the dispersion of NiSb particles in the CoSb3 matrix.