Thermal conductivity of fully filled skutterudites: Role of the filler

Using ab initio calculations we have investigated the lattice thermal conductivity (κ) of CoSb₃ and BaCo₄{Sb}₁₂$. The calculated room temperature ${κ}$ of these compounds are 11.5 and 6.1 W/m K, respectively. The change in ${κ}$ upon filling is mainly due to the reduction of phonon lifetimes limited by the anharmonic scattering, which occurs in the whole phonon spectrum, ruling out the postulated ``rattling'' model. We show that the harmonic interaction instead of the anharmonic interaction between the filler and the host matrix, depressing the phonon spectrum, is at the origin of the reduction of κ upon filling. We believe that the filler plays the same role in other fully filled skutterudites.