The polymorphism of samarium fullerides

Three different SmxC60 intercalation compounds have been identified. Sm2.75C60 has Pa3̄ symmetry and is characterized by tetrahedral cation vacancy-ordering. This phase coexists with a Pm3̄ Sm3C60 phase, under non-equilibrium conditions, when the metal concentration is increased in the mixture. A bcc Sm6C60 compound represents the upper limit of the doping level. The same behaviour was observed previously in the case of europium fullerides. The possibility that several oxidation states for both anions and cations may exist in M2.75C60 systems is examined.