Effect of Yb Filling on Thermoelectric Properties of Ge-Substituted CoSb₃ Skutterudites

Abstract

We report the effect of Yb filling on the thermoelectric properties of polycrystalline Ge-substituted CoSb₃ skutterudite compounds. Electrical conductivity, Seebeck coefficient, Hall effect, and thermal conductivity measurements were performed on polycrystalline Yb_yCo₄Ge_0.5Sb_11.5 (y=0, 0.1, 0.2, 0.3, 0.4 and 0.5). In Yb_yCo₄Ge_0.5Sb_11.5, the Ge atom acts as an electron acceptor that charge compensates for the Yb ions, resulting in p-type carrier conductivity at low Yb compositions y=0 and 0.1 and n-type one at high y=0.2–0.5. Due to the effect of charge compensation for Yb ions by Ge substitution, the Yb filling fraction limit in Yb_yCo₄Ge_0.5Sb_11.5 is larger than that in Yb_yCo₄Sb₁₂. The lattice thermal conductivity for Yb_yCo₄Ge_0.5Sb_11.5 drastically decreases from 8 W/(m·K) (y=0) to 2.4 W/(m·K) (y=0.5) with increasing Yb composition. The marked reduction of the lattice thermal conductivity can be attributed to the increase in the filling fraction of Yb, whose localized thermal vibration, “rattling” motion, substantially contributes to the scattering of phonons. The influence of Ge substitution on the thermoelectric properties in Yb_yCo₄Ge_0.5Sb_11.5 is also discussed.