Transmission electron microscopy, electron diffraction and hardness studies of high-pressure and high-temperature treated C-60

TEM and electron diffraction investigations were performed on high-temperat ure and high-pressure treated polymeric C-60 fullerene, prepared at 700, 77 3 and 800 K in the pressure range of 3-9 GPa, for one hour. A mixed phase o f alternating rhombohedral lamellae and tetragonal domains is formed, even at high pressures, with the ratio of polymers being dependent on the pressu re 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 t imes of 0.5-30 minutes for the graphitic phase showed the kinetics of graph itization to be slow (similar to1 h) and proceeding via cross-linked interm ediates containing trapped whole C-60 cages. The influence of the cross-lin king resulted in hardness values up to 33.5 GPa, for a twenty-minute treatm ent.