Compressibility of M3C60Fullerene Superconductors: Relation BetweenTcand Lattice Parameter

Abstract
X-ray diffraction and diamond anvil techniques were used to measure the isothermal compressibility of K3C60and Rb3C60, the superconducting, binary alkali-metal intercalation compounds of solid buckminsterfullerene. These results, combined with the pressure dependence of the superconducting onset temperatureTcmeasured by other groups, establish a universal first-order relation betweenTcand the lattice parameteraover a broad range, between 13.9 and 14.5 angstroms. A small second-order intercalate-specific effect was observed that appears to rule out the participation of intercalate-fullerene optic modes in the pairing interaction.