Local static distortion of rare earth ions in ROs4Sb12 (R=La, Ce, Pr, Nd, Sm) by extended X-ray absorption fine structure

Extended X-ray absorption fine structure (EXAFS) measurements have been carried out on ROs4Sb12 (R=La, Ce, Pr, Nd, Sm) to study the motion of rare earth ions accommodated in the Sb icosahedron cage. The temperature dependences of the thermal (Debye-Waller) factors were analyzed from 15 to 300K. The Einstein temperature obtained from EXAFS analysis of SmOs4Sb12 is the lowest of the compounds, while there are no significant differences among the other compounds. The local static disorder obtained from the temperature dependence of EXAFS shows good correlation with the space inside the Sb icosahedron cage. Effective static distortion is expected to occur when the cage space is larger than about 0.5 A. (author)