Refined crystal structure and mechanical properties of superhard BC4N crystal:: First-principles calculations

Synthesized cubic BC4N with Vickers hardness 10% higher than that of cubic BC2N exhibits a strange X-ray diffraction spectrum, assigned as a zinc-blende cubic structure. However, its crystal structure cannot be constructed with a zinc-blende structure as viewed from the stoichiometric formula. We found that this structure can be described by 3C-BC4N in Ramsdell notation, with the space group of P3ml. First-principles calculations show that this so-called cubic BC4N is a large gap insulator and has outstanding mechanical properties such as an ideal tensile strength of 77.1 GPa and a theoretical Vickers hardness of 84.3 GPa. The simulated Raman spectra of five 3C-BC4N configurations show totally different features, providing a valid method to conclusively determine the atomic arrangement of cubic BC4N.