Synthesis and properties of alkali-alkaline earth ternary superconducting fullerides.

Two kinds of Ba-including superconducting fullerides are reported. Nonavalent fulleride compounds A(3)Ba(3)C(60) (A = K, Rb, and Ca) were synthesized by intercalating alkali metals into preformed Ba3C60. A(3)Ba(3)C(60) is an isostructural series of bcc compounds, where the lattice parameters are changed keeping the formal valence of Cao molecule at 9-. In sharp contrast to the standard A(3)C(60), T-c decreases with increasing the lattice parameter. The superconducting phase of binary Ba4C60 was found to be octavalent Ba4C60 by synthesis of single phase material. The crystal structure of Ba4C60 is orthorhombic with the space group of Immm. These results indicate that superconductivity in Ba-including compounds occurs irrespective of the band-filling and crystal structure.