NEUTRON-DIFFRACTION AND STRUCTURAL MODELS OF RBC60 PHASES

Pair distribution functions (PDFs), obtained from powder neutron diffr action measurements have been used to construct structural models for the body centered orthorhombic (bco) and fee phases of RbC60. The PDF exhibits small differences, primarily due to the shortened inter-fulle rene: distance in the bco phase. The bco-RbC60 system is well fit to a model derived from first-principles quantum molecular dynamics in whi ch the C-C interfullerene distance is 1.57 Angstrom. While the geometr y of the interfullerene linkages is similar to a previously proposed m odel, the present results imply less distortion of the C-60 molecules and larger interfullerene distances. The PDF analysis also indicates s ignificant orientational disorder between chains of linked molecules.