Synthesis and Thermoelectric Properties of Partially Double-Filled (Ce1-zPr z) yFe4-x Cox Sb12 Skutterudites

Partially double-filled p-type (Ce1-zPr (z))(y) Fe4-xCoxSb12 (z = 0.25, 0.75; y = 0.8; x = 0, 0.5, 1.0) skutterudites were synthesized by encapsulated melting and consolidated by hot pressing. The microstructure, phase, charge transport characteristics, and thermoelectric properties of the hot-pressed specimens were analyzed. Detailed measurements indicated that the skutterudite phase was successfully synthesized, but a small amount of a secondary phase (FeSb2) was also identified. However, the amount of the FeSb2 phase decreased with an increase in the Co substitution. Unlike for the filled Ce1-z Pr (z) Fe4-x Co (x) Sb-12 skutterudites with y = 1, the (Ce,Pr)Sb-2 phases were not formed by partial filling with Ce/Pr. The electrical conductivity decreased with increasing temperature, similar to the behavior shown by degenerate semiconductors. The Hall coefficient and the Seebeck coefficients were positive, indicating that all specimens exhibited p-type characteristics. The electrical conductivity and the electronic thermal conductivity decreased with increasing Pr filling and Co substitution because of the decreased carrier concentration caused by charge compensation. A maximum dimensionless figure of merit, ZT(max) = 0.84, was obtained at 623 K for (Ce0.75Pr0.25)(0.8)Fe3CoSb12.