Transmission electron diffraction of the ordering transformation in crystalline C60

Transmission electron diffraction is used to define the ambient-temperature structure of sublimated pure C60 crystals and examine the ordering transformation that occurs below 249 K. Convergent-beam electron-diffraction analysis of the symmetry of the [100] pattern for the ambient-temperature phase indicates an Fm3»m structure. Analysis of [100], [110], and [111] high-symmetry zone-axis diffraction patterns of the low-temperature ordered phase indicate that the structure belongs to space group Pa3». Crystals with 111 (hexagonal plates) as well as those with other surface normals (rectangular 110 or 100 crystals) were found in the sublimated material. Electron-energy-loss near-edge fine structure demonstrates that significant bonding changes do not accompany the ordering. A twin with a (110) habit plane is identified in the ordered phase.