C. Meingast, G. Roth, M. M. Kappes, R. H. MIchel, C. Stoermer, L. Brard, P. A Heiney, J. E. Fischer, A. B. Smith, III, and R. M. Strongin, in "Physics and Chemistry of Fullerenes and Derivatives," pp. 167-170, H. Kuzmany, J. Fink, M. Mehring, and S. Roth eds, World Scientific, Singapore (1995).
The thermal expansion of the crystalline fullerene derivatives C60-O and (epoxide) and C61H2 (6,5 annulene) has been measured using a high resolution capitance dilatometer between 5 and 300 K. The results show that both solids undergo a sqequence of transitions similar to that found in pure C60, i.e. a first-order 'orientatinoal' ordering transition just below room temperature followed by an orientational glass transition at lower temperatures. The glass transition temperature Tg, which occurs near 90 K in C60, is shifted to ~100 K for C60-O and to ~135 K for C61H2 indicating a larger potential barrier to reorientation. In contrast to C60, the expansivity of both C60-O and C61H2 increases above Tg.