Effects of pressure on the structural, mechanical and anisotropic behavior of BC8N compound

Abstract

The pressure dependent behaviors on structural, mechanical and anisotropic properties are very important for superhard materials due to their widespread industrial applications. Here, a comprehensive analysis of the structural, mechanical and anisotropic behavior of three BC8N phases (denoted as BC8N-1, BC8N-2, and BC8N-3) under pressure are present by first principles calculations. Initially, the optimized structural parameters are consistent with the available theoretical results. Furthermore, it is found that the three phases of BC8N are structural stability under pressure. The elastic constants show an increasing tendency, and keep mechanically stable within the considered pressure. From the calculated B/G and Poisson’s ratio, it is predicted that the three phases of BC8N are brittle materials at low pressure, but strongly prone to ductility when the pressure is above 257.5, 254 and 259.5 GPa, respectively. The calculated hardness suggests that all three phases of BC8N belong to superhard materials, the order of hardness from high to low is BC8N-3 >BC8N-1 >BC8N-2. However, the hardness of BC8N-1 and BC8N-2 are less than 40 GPa when the pressure increasing to 315.4 and 329.1 GPa, respectively, which indicated that they no longer belong to the class of superhard materials. Finally, the pressure-induced anisotropic behavior has been also analyzed. It will provide a more comprehensive understanding for B-C-N compounds.