Hard and superhard carbon phases synthesized from fullerites under pressure

Abstract

A review has been presented on the structural and mechanical properties of hard carbon phases synthesized from fullerite C60 under pressure. The density and nanostructure have been recognized as the key parameters defining the mechanical properties of hard carbon phases. By suggesting a version of the transitional high-pressure diagram of C60 (developed up to 20 GPa), the three areas of the formation of hard carbon phases have been highlighted. The corresponding phases of superhard carbon are (1) disordered sp2-type atomic structures at moderate pressures and high temperatures (> 1100 K), (2) three-dimensionally polymerized C60 structures at moderate temperatures and high pressures (> 8 GPa), and (3) sp3-based amorphous and nanocomposite phases at high pressures and temperatures. First region can be in turn separated into 2 subparts with different peculiarities of sp2 structures and properties: low pressure part (0.1–2 GPa) and high-pressure part (2–8 GPa). Temperature can be recognized as a factor responsible for the formation of nanostructures by the partial destruction of molecular phases, whereas pressure is a factor responsible for stimulating the formation of rigid polymerized structures consisting of covalently bonded C60 molecules, whereas the combination of both factors leads to the formation of atomic-based phases with dominating sp3 bonding.