Thermoelectric properties of double-filled Pr1-z Nd z Fe4-x Co x Sb12 skutterudites

Abstract

Pr1-z Nd z Fe4-x Co x Sb12 (z = 0.25, 0.5, 0.75 and x = 0, 0.5, 1.0) skutterudites were synthesized by encapsulated melting and annealing, and were consolidated by hot pressing. The effects of Pr/Nd double filling and Co substitution for Fe (charge compensation) on the electronic transport and the thermoelectric properties were examined. The main phase of all specimens was the skutterudite phase, but a small amount of the FeSb2 phase was also found. An increase in the Co content suppressed the formation of the FeSb2 phase, but the (Pr,Nd)Sb2 phase was also produced in the Pr1-z Nd z Fe3CoSb12 specimens. Pr and Nd were confirmed to have successfully double-filled the voids and Co was confirmed to have substituted for Fe because the lattice constant decreased with increases in the Nd and the Co contents. The electrical conductivity slightly decreased as the temperature was increased, showing a degenerate semiconductor behavior. The Hall coefficient and the Seebeck coefficient showed positive signs, indicating that the major carriers were holes (p-type conduction). Although the electronic transport properties rarely changed with the Pr and the Nd filling fractions, the Seebeck coefficient increased slightly because the effective carrier mass increased as the Pr content was increased. Moreover, the Seebeck coefficient increased due to a decrease in the carrier concentration as the Co content was increased while the electrical conductivity and the thermal conductivity decreased. The maximum power factor, PF = 3.1 mWm -1K -2, and the maximum dimensionless figure of merit, ZT = 0.83, were obtained at 823 K for Pr0.75Nd0.25Fe4Sb12.