SOLVENT EFFECTS ON SUPERCONDUCTING ALKALI-METAL INTERCALATED C-60 PREPARED FROM LIQUID-AMMONIA STUDIED BY SOLID-STATE NMR

The directly isolated precipitate of RbxC60 from liquid ammonia contai ns solvent molecules, NH3. Thermal treatment is necessary to remove am monia solvent molecules from the lattice as well as to homogenize the Rb distribution within the synthetic product, to produce a face-center ed cubic (fee) unit cell. This latter unit cell is the form of Rb3C60 which shows superconductivity. The superconducting transition temperat ure, T-c, is found to be lower in Rb3C60 samples prepared from liquid ammonia than from those prepared by a conventional vapor transport tec hnique. The depression of T-c can be explained in terms of a large deg ree of orientational disorder of C-60 ions; along with effects of a tr ace amount of residual NH3, as suggested from solid-state NMR results.