Relation of structure and superconducting transition temperatures in A3C60

The preparation of a series of single-phase, isostructural fcc superconductors with composition A3C60 (where A is K, Rb, Cs, or a mixture of these) is reported, and it is shown that Tc increases monotonically with the size of the unit cell. Extended Hueckel band-structure calculations also show a monotonic increase in the density of states at the Fermi level, N(Ev), with lattice parameter. The primary implication of these results is that all A3C60 superconductors have the same structure and that changes in Tc can be accounted for by changes in N(Ev). (C.D.)