Thermoelectric properties of Co4−xMnxSb12−ySny skutterudites

Mn/Sn-doped CoSb 3 (Co 4-x Mn x Sb 12−y Sn y ) skutterudites were synthesized by mechanical alloying, and their thermoelectric properties were examined. A single δ-phase was obtained successfully by post-annealing and hot pressing; however, MnSb phase was observed in Co 2.5 Mn 1.5 Sb 12 and Co 3 MnSb 11.2 Sn 0.8 specimens. Temperature dependence of the electrical conductivity suggests that the Mn/Sn-doped specimens are degenerate semiconductors. Every specimen had a positive Seebeck coefficient, and a Co 3 MnSb 11.6 Sn 0.4 specimen exhibited the highest value. Mn doping caused a decrease in the Seebeck coefficient, but it could be enhanced by Mn/Sn double doping, possibly due to charge compensation. The thermal conductivity was desirably very low, and this originated from ionized impurity-phonon scattering. Thermoelectric properties were remarkably improved by Mn/Sn doping, and a maximum figure of merit, ZT = 0.54 was obtained at 723 K in the Co 3 MnSb 11.6 Sn 0.4 specimen.