Synthesis of superhard cubic BC2N

Cubic ${\mathrm{BC}}_{\mathrm{2}}\mathrm{N}$ was synthesized from graphite-like ${\mathrm{BC}}_{\mathrm{2}}\mathrm{N}$ at pressures above 18 GPa and temperatures higher than 2200 K. The lattice parameter of $\mathrm{c-}{\mathrm{BC}}_{\mathrm{2}}\mathrm{N}$ at ambient conditions is 3.642(2) Å, which is larger by 1.48% than would be expected based on ideal mixing between diamond and cubic boron nitride. The bulk modulus of $\mathrm{c-}{\mathrm{BC}}_{\mathrm{2}}\mathrm{N}$ is 282 GPa which is one of the highest bulk moduli known for any solid, and is exceeded only by the bulk moduli of diamond and $\mathrm{c-}\mathrm{BN}.$ The hardness of $\mathrm{c-}{\mathrm{BC}}_{\mathrm{2}}\mathrm{N}$ is higher than that of $\mathrm{c-}\mathrm{BN}$ single crystals which indicates that the synthesized phase is only slightly less hard than diamond.