STRUCTURE OF SINGLE-PHASE SUPERCONDUCTING K3C60

RECENT reports 1-3 of superconductivity in alkali-metal-doped compounds of the icosahedral C60 (buckminsterfullerene) molecule have attracted great experimental and theoretical interest. Superconductivity was originally discovered in samples prepared from gas-solid reactions 1, which made it impossible to determine the composition or structure of the superconducting phase. Holczer et al. 4 demonstrated that potassium-doped C60 has only a single stable superconducting phase, K3C60, with a transition temperature of 19.3 K. Improvements have since resulted in the preparation of 100% bulk superconductors 3. Because of the absence of impurity phases, we have been able to perform accurate Rietveld analysis of X-ray diffraction data from the superconducting phase. Here we report our results for the crystal structure of K3C60, determining that this superconducting compound has a face-centred cubic structure with a well defined stoichiometry. These results should open the way to rigorous description of the normal and superconducting properties of this compound.