K. Mizoguchi et al., NUCLEAR-MAGNETIC-RESONANCE STUDY OF FULLERENE SOLIDS AND THEIR COMPOUNDS, Materials science & engineering. B, Solid-state materials for advanced technology, 19(1-2), 1993, pp. 146-153
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.