Among different hypotheses, the most stable structure is based on BC2N2 tetrahedra with a stacking resembling tetragonal 'glitter' C 6 . Such BC 2 N 2 tetrahedral arrangement seems to be preferable in the case of the ternary B-C-N phases. The energetic stability ensured from the cohesive energy was further confirmed for the mechanical and dynamic stabilities based on elastic constants and phonon band structures. Tetragonal BCN is a superhard phase that is harder than cubic boron nitride and possibly more thermally and chemically stable than diamond.