Structural, anisotropic elastic and thermal properties of MB (M=Ti, Zr and Hf) monoborides

To better clarify and understand the applications of the transition-metal monoborides, first principles calculations were performed to investigate the structural properties, phase stability, elastic properties, and thermal conductivity of NaCl-type, FeB-type and CrB-type MB (M=Ti, Zr and Hf) monoborides. The results of equilibrium structures, cohesive energies and formation enthalpies are in good agreement with available experimental and other theoretical data. Based on the elastic constants, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio, are obtained by Voigt–Reuss–Hill approximation. All these monoborides are mechanically stable. The elastic anisotropies of monoborides are investigated via the various anisotropic indexes and the 3D surface constructions, and the order of elastic anisotropy is NaCl-type>CrB-type>FeB-type. By using the Cahill’s model, the minimum thermal conductivities of these monoborides were also investigated, and the results indicate that the minimum thermal conductivities show a dependence on direction.