Formation Of The High Pressure Graphite And Bc8 Phases In A Cold Compression Experiment By Raman Scattering

We use Raman scattering to study phase transition in the graphitic g-BC8 phase and graphite at high pressure up to 84GPa. The E-2g Raman active mode of graphite (G peak) can be detected up to 84GPa. We demonstrate that there is (1) a phase transition in g-BC8 and in graphite at 35GPa and (2) that above 35GPa, the g-BC8 and graphite transform under high pressure to possibly fully sp(3)-bonded, disordered hp-BC8, and hp-C phases. Below the phase transition, a polynomial fit to the G peak position versus pressure data yielded a quadratic relation; above the phase transition, it demonstrates linear behavior. The phase transition at high pressure in BC8 system and graphite is reversible. Quenched hp-BC8 and hp-C phases have the Raman spectrum typical to that of the graphitic phases. Copyright (c) 2013 John Wiley & Sons, Ltd.