Neutron scattering study on rattling in filled-skutterudite compounds

Kaneko, Koji   ; Matsuda, Tatsuma; Kimura, Hiroyuki*; Noda, Yukio; Metoki, Naoto   ; Momma, Koichi*; Izumi, Fujio*

Recently, a large-amplitude thermal vibration of a guest ion inside an oversized cage, called rattling, is considered to play a vital role for unconventional physical properties in . A precise single-crystal neutron diffraction and a maximum-entropy analysis are powerful method to reveal unconventional motion of rattling ions; this combination enables us a model-independent analysis to obtain an time-averaged picture of rattling motion in real space. Widely distributed anisotropic nuclear densities of in the Sb icosahedron cage were revealed in PrOsSb, NdOsSb and PrRuSb at room temperature. Note that a substantial difference was found in a distribution of rattling ions between Sb with =Os and Ru. The difference between Sb with =Os and Ru implies that the size mismatch is not a necessary and sufficient condition for anharmonicity, and may related to the cage type in skutterudites.