Prediction on the high-pressure physical properties of a new metastable structure for BC<sub>2</sub>N compound

Abstract

Light elements boron (B), carbon (C) and nitrogen (N) have small atomic radius and strong bonding ability, and the formed compounds are easy to form strong covalent bonds and high atomic density three-dimensional networks structures, makes it an alternative system for the preparation of superhard materials. Based on the newly studied body-centered tetragonal carbon structure model with excellent mechanical properties, a new structure of BC2N potential superhard compound with tetragonal symmetry structure and space group of I 4/ mmm was constructed in this paper. Using the first-principles calculation method based on density functional theory, the thermodynamic, mechanical and dynamic stability of the new tetragonal phase structure of the compound was systematically studied. It is shown that the tetragonal phase BC2N is atable in mechanics and dynamics at least in the pressure range of 0– 60 GPa. The thermodynamic calculation results show that the structural formation energy is slightly higher than the most stable wurtzite structure in the BC2N compound, indicating that the newly constructed tetragonal structure is a metastable structure of the BC2N compound, and its incompressibility is greater than other boron-carbon-nitrogen materials such as B2CN and BC4N. Based on the structural stability study, the electronic structure of the tetragonal BC2N in the pressure range of 0– 60 GPa is calculated. It is found to have a bandwidth of 2.16 eV at zero pressure, which is a semiconductor, and with the increase of pressure, The band gap is gradually widened; the high-pressure elastic properties show that the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Debye temperature, minimum thermal conductivity and elastic wave velocity of the tetragonal structure of BC2N compound are all increased in different increasing tendency with pressure, it shows brittleness and its elastic anisotropy becomes more obvious under high pressure. At the same time, the large bulk modulus, large shear modulus and high Vickers hardness indicate that the constructed tetragonal structure with I 4/ mmm space group is a potential superhard new structure of BC2N compounds.