Transmission electron diffraction of the ordering transformation in crystallineC60

Transmission electron diffraction is used to define the ambient-temperature structure of sublimated pure ${\mathrm{C}}_{60}$ 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.