SUPERCONDUCTIVITY IN BARIUM FULLERIDE

INTERCALATING solid C60 with dopant atoms yields materials with a remarkable range of properties1. Alkali metal atoms, for example, readily form charge-transfer compounds2,3, A(x)C60 (where A is an alkali metal), which can be metallic, superconducting or insulating depending on the dopant concentration4-9. In all cases, the superconducting phase has a face-centred cubic (f.c.c.) structure and stoichiometry A3C60, which suggests a common mechanism for superconductivity dependent, at least in part, on the external coordination number of the C60 molecules. More recently, it has been shown10 that the alkaline earth metal calcium can also be intercalated with fulleride to form a superconducting phase, again with a f.c.c.-derived structure, near a Ca:C60 ratio of 5:1. Here we report the intercalation of fulleride with barium, in which a pure body-centred cubic phase with a lattice constant of 11.171 angstrom is realized near a stoichiometry of Ba6C60. This phase is also superconducting (with a transition temperature of 7 K), suggesting that the mechanism of superconductivity is related to an intrinsic property of the C60 molecules, rather than the external coordination number.