OCTAHEDRAL CATIONS IN RB3C60 - RECONCILIATION OF CONFLICTING EVIDENCEFROM DIFFERENT PROBES

There is an apparent contradiction between X-ray diffraction, NMR and extended X-ray-absorption fine-structure (EXAFS) measurements on the s tructure of Rb3C60. Specifically, a possible displacement of the octah edral alkali cations away from their site center and the origin of a t hird observed Rb NMR line have been widely discussed. We address this question with X-ray powder diffraction as a function of temperature an d find that the octahedral cation does have its equilibrium position a t the site center with a large Debye-Waller factor. We show how this r esult can be reconciled with results of NMR and EXAFS.