Transformations of C60 fullerite in the regions of stability and instability of diamond on the carbon phase diagram in the pressure range of 20–160 GPa and temperatures of 300–2300 K

Abstract

The transformation features of C₆₀ fullerite have been studied in three regions of the recently updated carbon phase diagram at temperatures reaching 2300 K and pressures of 20–25 GPa (within the diamond stability region), 70 GPa (within the diamond instability region), and 160 GPa (also within the diamond stability region). The effect of resonant Raman scattering is observed in fullerite samples after treatment with a pressure of 20–25 GPa, depending on the synthesis temperature. When fullerite is heated under a pressure of 20–25 GPa, partial diamond formation is observed. An increase in pressure up to 160 GPa and heating to 2300 K does not result in the formation of diamond from fullerite, although at pressures above 115 GPa graphite is transformed into diamond. The observed effect can be explained by the fact that a denser structure than diamond is formed from fullerite at a pressure above 30 GPa. Therefore, the issue of the stability of the carbon phase at pressures exceeding 115 GPa remains a topic for further investigation.