Thermoelectric properties of the skutterudite Co1-xFexSb3 system

We have examined the phase equilibrium and thermoelectric properties of Co1-xFexSb3 ternary system up to high iron context x = 0.40. Traces of Sb were observed in the hot- pressed samples with x greater than or equal to 0.06, and FeSb2 (Fe0.73Co0.27Sb2) compound with marcasite structure was also observed in the samples with x greater than or equal to 0.25 by x-ray diffraction. The lattice parameter of Co1-xFexSb3 is slightly larger than that of the binary compound CoSb3. The Seebeck coefficient and the electrical resistivity are generally reduced by the substitution for Co by Fe. The thermal conductivity is also reduced by the substitution especially at high iron content region. These behaviors of the thermoelectric properties in the samples with low iron content are ascribed to the substituted Fe, while those in the samples with high iron content are ascribed to the precipitated FeSb2 (Fe0.73Co0.27Sb2) compound. For x <0.04, the figure of merit for Co1-xFexSb3 decreases with increasing x. However, above x =0.06 the figure of merit increases with x and as a result, Co0.75Fe0.25Sb3 has a maximum value of figure of merit of 4.8 x 10(-4) K-1 at 773 K. This value is much larger than the maximum value for CoSb3 3.2 x 10(-4) K-1 at 482 K. (C) 1998 American Institute of Physics. [S0021-8979(98)04724-0].