Influence of the pressure-temperature treatment on the polymerization of C60 single crystals at 2Â GPa-700Â K

X-ray diffraction and Raman spectroscopy have been used to characterize the structures obtained when C60 single crystals are treated at 2 GPa-700 K. Two different experimental procedures have been applied: the temperature is raised before the pressure is applied, or the opposite. The “heating-then-pressing” path leads to the tetragonal polymer structure (P42/mmc) together with a minor fraction of rhombohedral structure, which confirms previous results. In contrast, the “pressing-then-heating” path leads to a different state presenting similarities with both the rhombohedral and the disordered dimer structures. The results are discussed in light of the orientational and dynamical aspects of the C60 polymerization.