The well-characterized vacancy-ordered structure of this material was interpreted in terms of a simple electrostatic-energy model. The results provided useful insights into the structural distortions that were introduced locally by tetrahedral cation vacancies, and the model could be applied to alkali-metal and alkaline-earth fullerides. When applied to monovalent fullerides, the model clearly showed that the electrostatic force between an O cation and a neighboring T-site vacancy was very large. Therefore, in materials such as Rb3C60, which exhibited T-site vacancies, the surrounding O-site cations would undergo off-center displacements towards the vacancy; within the limits set by cation size. Such displacements were expected to be more difficult to detect there, than in Yb2.75C60, because of the disordered arrangement of the vacancies. The displacements were also expected to inhibit strongly any vacancy hopping; a process which had been proposed in order to explain the splitting of T-site nuclear magnetic resonance lines in Rb3C60.

K.M.Rabe, P.H.Citrin: Physical Review B, 1998, 58[2], R551-4