Abstract
Nuclear magnetic resonance (NMR) studies of the novel materials C 60 and C 70 and their compounds with the alkali metals are reported. The 13C NMR spectra and spin-lattice relaxation time T 1 of pure fullerene solids give insights into the rotational dynamics of C 60 and C 70 molecules, and a variety of dynamics, depending on the different preparation methods of the samples. A sharp change in T 1 with a small hysteresis of 1 K was observed in the C 60 powder prepared by a sublimation method at 263 K, corresponding to an orientational phase transition. A rugby-ball-shaped C 70 molecule, instead of the spherical C 60, shows uniaxial rotation between about 180 and about 280 K and three-dimensional rotation above about 340 K in the sublimated powder. 133Cs NMR of CsRb 2C 60 ( T c = 31 K )_and Cs 2RbC 60 ( T c = 33 K ) revealed that the bigger Cs atoms selectively occupy the bigger octahedral site, instead of the other two tetrahedral sites in the face-centered cubic structure of CsRb 2C 60, and that the valence of Cs was approximately unity. The 13C NMR and T 1 results of the three superconducting compounds was analysed to determine a relationship between T c and the density of states at the Fermi energy.
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