Investigation of the Anharmonic Guest Modes in Filled Skutterudites Using Inelastic X-ray Scattering Techniques

We have carried out high-resolution inelastic X-ray scattering and 149 Sm nuclear resonant inelastic scattering to investigate the anharmonicity of the mode of the atoms enclosed in the cages of filled skutterudites. The temperature dependence of the phonon energy obtained by 149 Sm nuclear resonant inelastic scattering from SmRu 4 P 12 suggests an anharmonic vibration of the Sm atoms. A similar decrease of the vibration energy of the La atoms in LsOs 4 Sb 12 with decreasing temperature, which suggests that this motion too is anharmonic, was observed by high resolution inelastic X-ray scattering.