STRUCTURE AND PROPERTIES OF SUPERCONDUCTING AND NONSUPERCONDUCTING ALKALI-METAL FULLERIDES AXC60 (A = NA, K, RB, OR CS)

Shielding diamagnetism and X-ray powder diffraction were used to characterize alkali-metal fullerides of sodium, potassium, rubidium, and cesium. The superconducting phase in both the potassium and rubidium systems has the composition A3C60 and a face centered cubic structure with alkali metal filling all octahedral and tetrahedral sites of close packed C60 layers. High pressure magnetic susceptibility measurements on K3C60 showed a negative pressure dependence on the superconducting transition temperature of -0.78 K/kbar. No evidence for superconductivity was observed in either the sodium or cesium systems, even though Na3C60 appears isostructural with K3C60 and Rb3C60.