Mechanical properties, minimum thermal conductivity, and anisotropy in bc-structure superhard materials

We conducted first-principles calculations to evaluate the elasticity, minimum thermal conductivity, and anisotropy of four orthorhombic superhard materials of bc-BxCyN and compared them with diamond and cubic boron nitride. All four bc-BxCyN materials are mechanically stable based on the basic evaluation of the mechanical stability of orthorhombic crystal. Our calculation results show that the bc-BC4N (x = 1, y = 4) material is the hardest among the bc-BxCyN models and has the highest values of elastic modulus and ideal strength. The bc-BC2N material ranks second and has a slightly lower hardness compared with bc-BC4N, and the bc-B2CN possesses the lowest hardness and weakest ideal strength. The elastic modulus and slowness of all four bc-BxCyN are anisotropic. In addition, the calculated minimum thermal conductivities at high temperatures show that bc-BC4N exhibits the highest thermal conductivity and bc-B2CN exhibits the lowest thermal conductivity. (C) 2015 Elsevier B.V. All rights reserved.