Order, Disorder and Structure of Crystals of C₆₀/C₇₀

Single crystals with two different morphologies, black and brown, of C₆₀ with about 12% C₇₀ have been studied by synchrotron X-ray diffraction. Integrated intensities from 8 reflections show that the charge distribution of the C₆₀ cluster is shell-like giving rise to an oscillatory behaviour in the diffracted intensities. From the intensities, the distance between diametrically opposite carbon atoms has been determined to be (7.24 ± 0.22) Å. The thickness of the charge distribution of the shell can be estimated as 3.06 Å and the cavity within a C₆₀ cluster to have a diameter of about 4.18 Å. The finite longitudinal width of the diffraction peaks from black crystals indicates a lack of long-range crystalline order. The rocking curves are about 7° broad and depict an unusually smooth behaviour. This may be indicative of a glassy or hexatic phase. High-resolution electron microscopy allows small crystallites with a relatively well-defined orientation relationship to be identified. In contrast, brown crystals have long-range order.