Novel (super)hard SiCN from crystal chemistry and first principles

The purpose of this work is to predict the existence of novel equiatomic SiCN based on tetragonal C6 structure (“glitter”), the elementary building unit being the 1,4 cyclohexadiene molecule comprising both tetrahedral (sp3) and trigonal (sp2) carbons. From crystal chemistry rationale the structural transformations of C6 to SiC2 and then to the ternary SiCN were fully relaxed to the ground states using first principles DFT-based calculation. Like early proposed C6 and SiC2, SiCN was found bonding and structurally stable from the elastic properties on one hand and dynamically stable from the phonons, on the other hand. The Vickers hardness of SiCN is close to that of cubic silicon carbide, a conventional superabrasive, whereas hardness of tetragonal SiC2 is slightly lower. Besides the abrasive properties, the electronic band structure indicates metal-like behavior of SiCN thus suggesting the potential for heat dissipation in operating conditions.