Visualization of anharmonic thermal vibration in filled skutterudite compounds

Single crystal neutron diffraction experiments were carried out on filled skutterudite compounds PrOs₄Sb₁₂ and NdOs ₄Sb₁₂ at room temperature. Analyses using maximum entropy method employed for the present study offers the possibility of revealing rattling of rare earth ions in LnOs₄Sb₁₂ without any specific model. The result of PrOs₄Sb₁₂ reveals the widely spread Pr nuclear density distribution at room temperature, which has a characteristic trapezoidal shape along the [100] direction with the width of roughly 0.58° Å in the full width at half maximum(FWHM). A resemblance is found for results of Nd in NdOs₄Sb₁₂ with slightly larger width of 0.75° Åin FWHM. These findings indicate the presence of strong anharmonicity for Ln sites in the Sb cage of both PrOs ₄Sb₁₂ and NdOs₄Sb₁₂.