Cerium filling and lattice thermal conductivity of skutterudites

We have investigated the structural and transport properties of filled skutterudites of the general form Ce_yFe_4-xCo_xSb₁₂. We show that the Ce occupancy of the cages is a strong function of the presence of cobalt, varying from an almost 100% filling for x=0 down to no more than 10% filling in pure Ce_yCo₄Sb₁₂, i.e., for x=4. We demonstrate a strong suppression of the lattice thermal conductivity by both the “rattling motion” of Ce, and by alloying Fe with Co. We propose that the partially filled skutterudites can be viewed as solid solutions of fully filled CeFe₄Sb₁₂ and □Co₄Sb₁₂, where □ stands for a vacancy