A Novel Superhard Tetragonal Carbon Mononitride

We introduced a novel carbon mononitride within tetragonal P4(2)/m symmetry motivated by experimental synthesis and theoretical predictions. Phonon dispersion and formation enthalpy calculations suggest that P4(2)/m-CN is dynamically stable at ambient conditions and can be synthesized at readily attainable pressures. The crystal orientation dependences of the Young's and shear moduli have been systematically studied for this P4(2)/m phase. Further mechanical calculations suggested that the P4(2)/m-CN is ultracompressible and superhard. The ideal tensile and shear strength at large strains of P4(2)/m-CN are also examined. The results suggest that the weakest tensile strength is along the [100] direction, and the atomic deformation mechanism of P4(2)/m-CN along the weakest shear strength direction (100)[010] is discussed.