Ce Filling Limit and Its Influence on Thermoelectric Performance of Fe 3 CoSb 12 -Based Skutterudite Grown by a Temperature Gradient Zone Melting Method.

CoSb ₃ -based skutterudite is a promising mid-temperature thermoelectric material. However, the high lattice thermal conductivity limits its further application. Filling is one of the most effective methods to reduce the lattice thermal conductivity. In this study, we investigate the Ce filling limit and its influence on thermoelectric properties of p-type Fe ₃ CoSb ₁₂ -based skutterudites grown by a temperature gradient zone melting (TGZM) method. Crystal structure and composition characterization suggests that a maximum filling fraction of Ce reaches 0.73 in a composition of Ce _0.73 Fe _2.73 Co _1.18 Sb ₁₂ prepared by the TGZM method. The Ce filling reduces the carrier concentration to 1.03 × 10 ²⁰ cm ^-3 in the Ce _1.25 Fe ₃ CoSb ₁₂ , leading to an increased Seebeck coefficient. Density functional theory (DFT) calculation indicates that the Ce-filling introduces an impurity level near the Fermi level. Moreover, the rattling effect of the Ce fillers strengthens the short-wavelength phonon scattering and reduces the lattice thermal conductivity to 0.91 W m ^-1 K ^-1 . These effects induce a maximum Seebeck coefficient of 168 μV K ^-1 and a lowest κ of 1.52 W m ^-1 K ^{- 1} at 693 K in the Ce _1.25 Fe ₃ CoSb ₁₂ , leading to a peak zT value of 0.65, which is 9 times higher than that of the unfilled Fe ₃ CoSb ₁₂ .