Thermoelectric properties of indium-filled skutterudites

Structural, electrical, and thermal transport properties of CoSb3 partially filled with indium are reported. Polyerystalline samples of InxCO4Sb12 (0 <= x <= 0.3) were prepared by solid-state reaction under a gas mixture of 5% H-2 and 95% Ar. The solubility limit of the indium filling voids in CoSb3 was found to be close to 0.22. Synchrotron X-ray diffraction refinement of the x = 0.2 sample showed that the indium is located in the classic rattler site and has a substantially larger thermal factor than those of Co and Sb. The electrical resistivity, Seebeck coefficients, and thermal conductivity of the InxCO4Sb12 samples were measured in the temperature range of 300-600 K. All samples showed metal-like behavior, and the large negative Seebeck coefficients indicated n-type conduction. The thermal conductivity decreased with increasing temperature for all samples. A thermoelectric figure-of-merit (ZT) >= 1 (n-type) has been achieved when x >= 0.2 in InxCO4Sb12 at 575 K.