NUCLEAR-MAGNETIC-RESONANCE STUDY OF FULLERENE SOLIDS AND THEIR COMPOUNDS

Nuclear magnetic resonance (NMR) studies of the novel materials C60 an d C70 and their compounds with the alkali metals are reported. The C-1 3 NMR spectra and spin-lattice relaxation time T1 of pure fullerene so lids give insights into the rotational dynamics of C60 and C70 molecul es, and a variety of dynamics, depending on the different preparation methods of the samples. A sharp change in T1 with a small hysteresis o f 1 K was observed in the C60 powder prepared by a sublimation method at 263 K, corresponding to an orientational phase transition. A rugby- ball-shaped C70 molecule, instead of the spherical C60, shows uniaxial rotation between about 180 and about 280 K and three-dimensional rota tion above about 340 K in the sublimated powder. Cs-133 NMR of CsRb2C6 0 (T(c) = 31 K) and Cs2RbC6, (T(c) = 33 K) revealed that the bigger Cs atoms selectively occupy the bigger octahedral site, instead of the o ther two tetrahedral sites in the face-centered cubic structure of CsR b2C60, and that the valence of Cs was approximately unity. The C-13 NM R and T1 results of the three superconducting compounds was analysed t o determine a relationship between T(c) and the density of states at t he Fermi energy.