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

Abstract

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 R1-yR ' yFexCo4-xSb12 double-filled skutterudite system (R, R ' = rare earth rattlers) because these need larger numbers of rattlers (approximate to 1.0) than are needed in the n-type skutterudite case (approximate to 0.3). We attempted to optimize the rattler fraction in a p-type CeyYb1-yFe3CoSb12 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 ohm(-1)cm(-2) at 723 K) of this Ce0.6Yb0.4Fe3CoSb12 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 (YbyFe3CoSb12, and CeyFe3CoSb12) previously reported by us. We found that filling with the Ce4+-rattler was more effective than filling with the Yb2+ for reducing the lattice thermal conductivity in the Ce-y Yb1-yFe3CoSb12 double-filler system. The Yb2+-filler effectively increased the electrical conductivity of the p-type Fe3CoSb12 filled skutterudite by modifying the carrier concentration.