Graphite at high pressures: Amorphization at 44 GPa

A Raman study of graphite-like modifications of carbon (monocrystalline graphite, pyrolytic graphite and amorphous (glassy) carbon) was performed at high pressures and room temperature. At P=23 GPa a transition of monocrystalline graphite into a transparent phase was observed, its Raman spectrum being typical of amorphous solids. The pressure dependence of Raman frequency of monocrystalline graphite reveals a step-like peculiarity at P=23–45 GPa. At P > 44 GPa an abrupt broadening of Raman bands of pyrolytic graphite and glassy carbon was observed and the Raman spectra of all three substances under study become practically indistinguishable from one another and from that of amorphous carbon (a-C) at the same pressure. This result is ascribed to the formation at these pressures of a dense amorphous carbon modification.