Rapid preparation of InxCo4Sb12 with a record-breaking ZT = 1.5: the role of the In overfilling fraction limit and Sb overstoichiometry

Abstract

Samples of indium-filled In_xCo₄Sb₁₂ skutterudite were successfully synthesized by conventional induction melting without the use of evacuated quartz ampoules. Addition of In above the filling fraction limit (x ≈ 0.22) and adjustment of Sb excess in the induction-melted In_xCo₄Sb₁₂ ingots allowed us to suppress formation of the unwanted CoSb₂ phase in the sintered samples and effectively control the amount of the InSb impurity phase which precipitated in nanometer-sized regions along the grain boundaries of the main skutterudite phase. Measurements of the Seebeck coefficient, electrical conductivity and thermal conductivity of the In_xCo₄Sb₁₂ samples with nominal In contents x = 0.2, 0.6, and 1.0 revealed a simultaneous increase in the electrical conductivity and decrease in the thermal conductivity. This results in the record value of the thermoelectric figure of merit ZT ≈ 1.5 for single-filled skutterudites which was attained in the In₁Co₄Sb₁₂ sample at 725 K.