(Rb x K ₁ – x ) ₃ C ₆₀ Superconductors: Formation of a Continuous Series of Solid Solutions

By means of an approach that employs alkali-metal alloys, bulk single-phase (RbxK1-x)(3)C(6O) 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(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(c)) increases linearly with x in this series of materials. The formation of a continuous range of solid solutions demonstrates that the rubidium- and potassium-doped C(60) superconducting phases must be isostructural, and furthermore, suggests that the linear increase in T(c) with x results from a chemical pressure effect.