Charge density study of C60 superconductors by MEM/Rietveld analysis

The charge density study of alkali metal doped fullerenes, Rb2CsC60, K2RbC60, Na2RbC60 and Li2CsC60, was carried out at room temperature by MEM/Rietveld analysis, which is the combination of the Maximum Entropy Method (MEM) and Rietveld analysis using synchrotron radiation powder data. The distinctly different features of charge densities of the C60 molecules relating to the superconducting properties were revealed in the obtained MEM charge densities. For Na2RbC60, K2RbC60 and Rb2CsC60, the rotations of the C60 molecules were virtually quenched while the C60 molecule in Li2CsC60 was in an orientational disorder. In the interatomic region, the overlapped charge density indicating the existence of a covalent bond was not found significantly between the C60 molecules and doped metal atoms for the four materials. However, in the MEM charge densities, the relative differences among them were found significantly for the charge deficiencies of the doped metal atoms which should be associated with charge transfer from the metal atoms to the C60 molecule.