Most likely phase of superhard BC2N by ab initio calculations

We predict a most likely structure of superhard BC2N, named z-BC2N, which is constructed from the sixteen-atom supercell of diamond by using first-principles calculations. z-BC2N is a more stable metastable phase with respect to other structures and has the tetragonal symmetry belonging to the space group P-42M. z-BC2N obeys the bond-counting rule that the chemical bonds in the unit cell consist of B-C, B-N, C-C, and C-N bonds, and C-C and B-N bonds are as many as possible. The calculated x-ray diffraction spectrum of z-BC2N agrees with the reported experimental result more well than the previously-predicted structures. Our results indicate that z-BC2N is perhaps the most likely structure of BC2N. Theoretical Vickers hardness and bulk modulus of z-BC2N are calculated to be 75.9 and 402.7 GPa exceeding those of cubic BN.