3.21 - Nanostructured Superhard Carbon Phases Synthesized from Fullerites under Pressure

Abstract

In this chapter, we present a review on the structural and mechanical characteristics of hard carbon phases synthesized from fullerite C60 under pressure. Density and nanostructure are recognized as the key parameters defining the mechanical properties of hard carbon phases. Suggesting a modified version of the transitional high-pressure diagram of C60 (developed up to 20GPa), we highlight the three regions of formation of hard carbon phases. The corresponding phases of superhard carbon are (1) disordered sp2-type atomic structures at moderate pressures and high temperatures (>1100K), (2) three-dimensionally polymerized C60 structures at moderate temperatures and high pressures (>8GPa), and (3) diamond-based amorphous and nanocomposite phases at high pressures and temperatures. The first region can be in turn divided into two subparts with different peculiarities of sp2-structure and properties: a low-pressure part (0.1–2GPa) and a high-pressure part (2–8GPa). Temperature can be recognized as a factor that is responsible for the formation of nanostructures by the partial destruction of molecular phases and pressure—as 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.