Transmission electron microscopy, electron diffraction and hardness studies of high-pressure and high-temperature treated C60

TEM and electron diffraction investigations were performed on high-temperature and high-pressure treated polymeric C-60 fullerene, prepared at 700, 773 and 800 K in the pressure range of 3-9 GPa, for one hour. A mixed phase of alternating rhombohedral lamellae and tetragonal domains is formed, even at high pressures, with the ratio of polymers being dependent on the pressure applied. At higher temperatures, 900-1173 K, and for a similar pressure range, graphitic 'hard' carbon phases formed, via an interpolymer interface instability and/or shear mechanism. This phase exhibited a hardness of 10-15 GPa and a high degree of elastic recovery under indentation. Treatment times of 0.5-30 minutes for the graphitic phase showed the kinetics of graphitization to be slow (similar to1 h) and proceeding via cross-linked intermediates containing trapped whole C-60 cages. The influence of the cross-linking resulted in hardness values up to 33.5 GPa, for a twenty-minute treatment.