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