(Rb sub x K sub 1 minus x ) sub 3 C sub 60 superconductors: Formation of a continuous series of solid solutions

By means of an approach that employs alkali-metal alloys, bulk single-phase (Rb{sub x}K{sub 1{minus}x}){sub 3}C{sub 60} superconductors have been prepared for all x between 0 and 1. For x = 1 it is shown that the maximum superconducting fraction, which approaches 100% in sintered pellets, occurs at a Rb to C{sub 60} ratio of 3:1. More importantly, single-phase superconductors are formed at all intermediate values of x, and it is shown that the transition temperature (T{sub c}) increases linearly with x in the series of materials. The formation of a continuous range of solid solutions demonstrates that the rubidium- and potassium-doped C{sub 60} superconducting phases must be isostructural, and furthermore, suggests that the linear increase in T{sub c} with x results from a chemical pressure effect.