Peculiarities of Graphite Transformation under High Pressure

Single crystal graphite specimens were compressed at a room temperature in the diamond anvil cell in the c-axis direction. High pressure values up to 58 GPa and shear deformation up to 30 degrees were used. We found out appearance of filament-like or lamella structures. Their appearance is result of formation of two mutually perpendicular frameworks of graphite. Schemes of possible co-arrangement of two mutually perpendicular graphite frameworks are proposed. This construction should lead to formation of straight lines of carbon atoms, which associated with sp(3)- bonds along this boundary. Presence of weak band at 1150 cm(-1) in Raman spectra as well as equality of intensity of D- and G- peaks can be considered as an evidence for the presence of sp(3)-bonds. We observed increase in elastic modulus of the surface of our specimens by Scanning Probe Microscopy method.