CRYSTAL-STRUCTURES AND THERMAL-EXPANSION OF FULLERENES

X-ray powder diffraction studies on pure C70 and C60 solids in the temperature range 298 - 773 K is reported. While the diffraction pattern of C70 at temperatures above 315 K could be indexed on a hexagonal cell, the room temperature pattern showed significant differences in terms of peak broadening and shoulder formation. This suggests an orientational ordering just above room temperature. The coefficient of linear expansion of C60 is found to be less than that of C70 which is only slightly lower than that of graphite (along c-axis).