Thermal Conductivity Reduction by Tuning the Rattler Fraction in a p-type CeyYb1−yFe3CoSb12 Double-filled Skutterudite

The rattling effect has been a major research topic in attempts to reduce high-frequency phonon conduction, especially for the skutterudite system. Filling skutterudite with rattler atoms with different localized frequencies (double-filling) has also been reported as an effective method to decrease the thermal conductivity. Optimization research for the double rattler effect is required, especially in the p -type R 1− y R′ y Fe x Co 4− x Sb 12 double-filled skutterudite system (R, R′ = rare earth rattlers) because these need larger numbers of rattlers (≈ 1.0) than are needed in the n -type skutterudite case (≈ 0.3). We attempted to optimize the rattler fraction in a p -type Ce y Yb 1− y Fe 3 CoSb 12 skutterudite system in this research. We combined a melt spinning (MS) process with a subsequent spark plasma sintering (SPS) technique to fabricate bulk nanocrystalline skutterudites. The resulting low thermal conductivity (2.20 Wm −1 K −1 at 723 K) and higher electrical conductivity (912 Ω −1 cm −2 at 723 K) of this Ce 0. 6 Yb 0.4 Fe 3 CoSb 12 double-filled system makes the maximum dimensionless figure-of-merit ( ZT , 0.90 at 723 K) in the double-filled specimen higher than those in the single-filled skutterudite systems (Yb y Fe 3 CoSb 12 , and Ce y Fe 3 CoSb 12 ) previously reported by us. We found that filling with the Ce 4+ -rattler was more effective than filling with the Yb 2+ for reducing the lattice thermal conductivity in the Ce y Yb 1− y Fe 3 CoSb 12 double-filler system. The Yb 2+ -filler effectively increased the electrical conductivity of the p -type Fe 3 CoSb 12 filled skutterudite by modifying the carrier concentration.