Thermal conductivity of fully filled skutterudites: Role of the filler

Using ab initio calculations we have investigated the lattice thermal conductivity () of CoSb₃ and BaCo₄Sb₁₂. The calculated room temperature of these compounds are 11. 5 and 6. 1 W/m K, respectively. The change in 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 upon filling. We believe that the filler plays the same role in other fully filled skutterudites.