G. B. M. Vaughan, P. A. Heiney, J. E. Fischer, D. E. Luzzi, D. A. Ricketts-Foot, A. R. McGhie, Y. W. Hui, A. L. Smith, D. E. Cox, W. J. Romanow, B. H. Allen, N. Coustel, J. P. McCauley, Jr., and A. B. Smith, III, Science 254, 1350-1353 (1991).
The high temperature structure of solvent-free C70 has been determined using high resolution x-ray powder diffraction and electron microscopy. Samples crystallized from solution form hexagonal-close-packed crystals which retain an appreciable amount of residual toluene, even after prolonged heating. Samples prepared by sublimation, which contain no detectable solvent, are primarily face-centered cubic with some admixture of a hexagonal phase. The relative volume of the hexagonal phase can be further reduced by annealing. The structures of both phases are described using a model of complete orientational disorder. The cubic phase contains an appreciable density of stacking faults along the [111] direction.
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