High-temperature structure of C60. An in situ X-ray diffraction study

High-purity C60 has been studied by in situ X-Ray Diffraction (XRD). Between 300 and 900 K, the volume thermal expansion coefficient is αv 4.57(4) x 10-5 K-1 with no observable deviations from linearity. Recrystallization is activated at T ≥ 600 K, as observed by the fast (< 5 s) and slow (> 10 min) variations in low-index Bragg intensities. At lower temperatures, thermal desorption of molecular oxygen at ∼ 420 K is accompanied with a step-wise increase of the 111-Bragg reflection intensity, but with no measurable change of the lattice parameter. The twin fault density has first been determined using high-resolution XRD. The twinning probability is 0.8%. Crystallites show a ± 0.3 intrinsic mosaic spread. Mechanical milling in acetone and in air increases the twinning probability to 1.8 and 3.1%, respectively. (orig.)