P.A. Heiney, J.E. Fischer, A.R. McGhie, W.J. Romanow, et al., "Orientation Ordering Transition in Solid C60," Physical Review Letters, 66:2911, 1991.
Paul A. Heiney (University of Pennsylvania, Philadelphia): "In materials such as liquid crystals or quasicrystals, the shape and symmetry of the constituent molecules or atomic clusters form the basis for unusual structural properties. The atoms in a `buckyball' (C60) form a sphere that is only slightly `bumpy.' Our X-ray measurements showed that at low temperature the bucky-balls freeze into a simple cubic lattice. Above 250 K, however, they begin to rotate, so that the buckyball orientations are random, though the molecular centers are still fixed on the crystal lattice. This picture was confirmed by 13C NMR measurements (R. Tycko, et al., Physical Review Letters, 67:1886, 1991).
"In addition to advancing our understanding of the role that molecular symmetry plays in determining crystalline structure and dynamics, the X-ray measurements presented...
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