Skutterudite: Reproducibility of Thermoelectric Performance of P-type R_yFe_4-xCo_xSb₁₂ Bulky Compacts

Abstract

Skutterudite compounds have excellent thermoelectric performance in the intermediate-to high temperature range. Their lattice thermal conductivity can be reduced by intensifying phonon scattering through independent vibrations of the guest atoms, by filling the voids within the lattice. Furthermore, the thermoelectric figure of merit (ZT) can be enhanced by optimizing the carrier concentration through charge compensation between transition elements. In this study, we compared the thermoelectric properties of p-type filled skutterudite materials, R_yFe_4-xCo_xSb₁₂, where R represents rare-earth elements (La/Ce/Pr/Nd/Yb), which were filled in the voids, and Co was charge-compensated at the Fe site. In the case of La_yFe_4-xCo_xSb₁₂, the introduction of La filling and Co doping led La_0.9Fe₃CoSb₁₂ to exhibit a high power factor and low thermal conductivity (ZT = 0.67 at 723 K). In the case of Ce_yFe_4-xCo_xSb₁₂, in addition to Ce filling, the substitution of Co for Fe resulted in additional lattice scattering, leading to a decrease in thermal conductivity. However, CeFe₄Sb₁₂ exhibited a maximum performance of ZT = 0.70 at 823 K. In the case of Pr_yFe_4-xCo_xSb₁₂, the thermal conductivity was reduced through phonon scattering induced by Pr filling and additional lattice scattering caused by Co substitution; as a result, Pr_0.8Fe₃CoSb₁₂ exhibited ZT = 0.89 at 723 K. In the case of Nd_yFe_4-xCo_xSb₁₂, the phonon scattering was enhanced by adjusting the filling of Nd and substitution of Co, resulting in a lower thermal conductivity; Nd_0.9Fe_3.5Co_0.5Sb₁₂ exhibited ZT = 0.91 at 723 K. For Yb_yFe_4-xCo_xSb₁₂, Yb_0.9Fe₃CoSb₁₂ exhibited a thermoelectric performance of ZT = 0.56 at 823 K. In addition, in this study, for the fabrication (application) of thermoelectric modules, the p-type Nd_0.9Fe_3.5Co_0.5Sb₁₂ skutterudite, which exhibited the best thermoelectric performance, was prepared in bulky compacts to verify the uniformity and reproducibility of its thermoelectric performance.