Substantial thermal conductivity reduction in mischmetal skutterudites MmxCo4Sb12 prepared under high-pressure conditions, due to uneven distribution of the rare-earth elements

Abstract

Thermoelectric mischmetal-filled Mm_xCo₄Sb₁₂ (Mm: natural cocktail of rare-earth elements, mostly Ce and La) skutterudites have been synthesized and sintered in one step under high-pressure conditions at 3.5 GPa in a piston–cylinder hydrostatic press. Synchrotron X-ray diffraction patterns display a splitting of the diffraction peaks ascribed to purely Ce-, and Mm-filled skutterudite phases, which have been analyzed and confirmed by high-resolution TEM and EELS. A total thermal conductivity (κ) of 1.51 W m⁻¹ K⁻¹ is measured at 773 K for Mm_0.5Co₄Sb₁₂, below that of other filled skutterudites, which is promoted by the enhanced phonon scattering over a broad range of the phonon spectrum due to the inhomogeneous and nanoscale mischmetal inclusion. Compared to undoped CoSb₃ skutterudite synthesized by conventional methods, κ is reduced by a factor of 3, while the power factor is also substantially enhanced.