Thermoelectric Properties of p-Type La1-zPrzFe4-xCoxSb12 Skutterudites

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) Sb-2 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.