Synthesis and thermoelectric properties of p-type double-filled La1−z Ce z Fe4−x Co x Sb12 skutterudites

Abstract

La1−z Ce z Fe4−x Co x Sb12 (0.25 ≤ z ≤ 0.75 and 0.5 ≤ x ≤ 1) skutterudites were synthesized, and the effects of La/Ce double filling and Co substitution on their transport and thermoelectric properties were examined. The formation of the skutterudite phase was confirmed and a small amount of secondary phases of FeSb2 and (La,Ce)Sb2 were observed. The lattice constant decreased with increasing Co and Ce contents, which meant that the substitution of Co for Fe and the filling of La and Ce had been successfully performed. All samples showed p-type characteristics with positive signs of the Hall coefficient and the Seebeck coefficient. The carrier concentration (the electrical conductivity) decreased with increasing Co and Ce contents due to the increased charge compensation and electron donation. The lattice thermal conductivity decreased with decreasing Co substitution, but the total thermal conductivity increased with decreasing Co substitution because the electronic thermal conductivity was dominant. La/Ce-double-filled La1−z Ce z Fe4−x Co x Sb12 skutterudites showed superior thermoelectric properties to La- or Ce-single-filled skutterudites due to their improved electrical properties and low lattice thermal conductivity. The maximum dimensionless figure of merit ZT = 0.79 was achieved at 823 K for La0.75Ce0.25Fe3.5Co0.5Sb12.