PRESSURE-DEPENDENCE OF THE SUPERCONDUCTING TRANSITION-TEMPERATURE IN NOMINAL RB0.5CS2.5C60

We report measurements of the superconducting transition temperature i n a compound with a nominal composition Cs2.5Rb0.5C60 under hydrostati c pressure of up to 15.5 kbars. We observe two transitions, at tempera tures T and T-c in this pelletized sample. We identify the lower temp erature transition T with the onset of intergranular shielding curren ts. The upper transition temperature T,(P) falls on a universal T-c(P) curve, defined from similar data obtained previously on K3C60 and Rb3 C60, after we shift the pressure axis for our data by -2.6 kbars. We i dentify T-c as a superconducting transition in Rb2CsC60 on the basis o f the compressibility analysis and published values of the lattice par ameters for alkali-doped C-60, as well as T-c(P = 0) and (dT(c)/dP)(p= 0).