P. A. Heiney, G. B. M. Vaughan, J. E. Fischer, N. Coustel, D. E. Cox, J. R. D. Copley, D. A. Neumann, W. A. Kamitakahara, K. M. Creegan, D. M. Cox, J. P. McCauley, Jr., and A. B. Smith, III, Phys. Rev. B45, 4544-4547 (1992).
X-ray and neutron diffraction measurements have been used to study the evolution of the lattice parameter of solid C60 through the orientational-ordering transition. The lattice parameter jumps by +0.044 +/- 0.004 Angstrom on heating, indicating a strongly first order transition. The average isobaric volume thermal expansion coefficient both above and below the transition is 6.2 +/- 0.2 X 10**(-5) / K . We observe phase coexistence over a 5 K range, but little if any hysteresis.
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