X. Chen et al., SOLVENT EFFECTS ON SUPERCONDUCTING ALKALI-METAL INTERCALATED C-60 PREPARED FROM LIQUID-AMMONIA STUDIED BY SOLID-STATE NMR, Chemistry of materials, 10(2), 1998, pp. 503-508
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.