Potential ultrahard nitride materials containing silicon, carbon and nitrogen

Abstract

Using ab initio and self-consistent-charge density functional based tight-binding electronic structure calculations the possibility that a recently synthesized layered structure of ${\mathrm{Si}}_{2}{\mathrm{CN}}_{4}$ can lead to superhard structures in the spinel or the $\ensuremath{\beta}$ phase is discussed. Both methods show that extensive compression of the layered phase leads to an abrupt breakdown of the N-C-N bonds. The compressed volume at which this occurs is above the volume belonging to the predicted transition pressures at which the layered phase and $\ensuremath{\beta}$ phases can coexist simultaneously. Kinetic factors are important in all cases.