Thermoelectric Properties of p-Type La1−z Pr z Fe4−x Co x Sb12 Skutterudites

Abstract

p-Type La1−zPrzFe4−xCoxSb12 skutterudites were prepared by encapsulated melting, quenching, annealing, and hot pressing. The skutterudite phase was successfully synthesized but small amounts of FeSb2 and (La,Pr)Sb2 secondary phases were also observed, especially for the Co-substituted specimens. Carrier concentration decreased with increasing Pr and Co content. Electrical conductivity decreased with increasing temperature, showing that all specimens were heavily-doped semiconductors. Electrical conductivity also decreased with increasing Pr and Co content. The Hall and the Seebeck coefficients revealed that all specimens had p-type characteristics. Seebeck coefficients increased with increasing temperature, with maximum values occurring between 723 and 823 K. The maximum power factor (PF) was 3.1 m Wm−1 K−2, at 823 K and 723 K for La0.75Pr0.25Fe4Sb12 and La0.75Pr0.25 Fe3.75Co0.25Sb12, respectively. Thermal conductivity decreased with increasing Pr and Co content, and increased because of bipolar conduction at temperatures above 723 K. For a fixed Co content, lattice thermal conductivity decreased with increasing Pr content; this may be attributed to a larger contribution from Pr than from La to the decrease in lattice thermal conductivity. The dimensionless figure of merit (ZT) had maximum values of 0.83 at 823 K for La0.75Pr0.25Fe4Sb12 and 0.81 at 723 K for La0.75Pr0.25Fe3.75Co0.25Sb12.