13 C NMR Spectroscopy of K x C 60 : Phase Separation, Molecular Dynamics, and Metallic Properties

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Abstract
The results of 13 C nuclear magnetic resonance (NMR) measurements on alkali fullerides K x C 60 are reported. The NMR spectra demonstrate that material with 0 < x < 3 is in fact a two-phase system at equilibrium, with x = 0 and x = 3. NMR lineshapes indicate that C 3– 60 ions rotate rapidly in the K 3 C 60 phase at 300 K, while C 6– 60 ions in the insulating K 6 C 60 phase are static on the time scale of the lineshape measurement. The temperature dependence of the 13 C spin-lattice relaxation rate in the normal state of K 3 C 60 is found to be characteristic of a metal, indicating the important role of the C 3– 60 ions in the conductivity. From the relaxation measurements, an estimate of the density of electronic states at the Fermi level is derived.