Mechanical and phonon properties of the superhard LuB2, LuB4, and LuB12 compounds

We have studied structural, elastic, and lattice dynamical properties of the LuB2, LuB4, and LuB12 compounds by using the plane-wave pseudopotential approach to the density-functional theory within the generalized gradient approximation. We have considered three different crystal structures of LuBx: LuB2 (P6/mmm), LuB4 (P4/mbm), and LuB12 (Fm-3m). The most stable structure is found to be tetragonal (P4/mbm) structure. The comparative results on the basic physical parameters such as lattice constants, bulk modulus, bond distances, elastic constants, shear modulus, Young's modulus, and Poison's ratio are reported. Also, we have predicted that LuB4 and LuB12 compounds are potential superhard materials. Furthermore, the phonon dispersion curves and corresponding phonon density of states (DOS) are computed for considered phases. Our structural and some other results are in agreement with the available experimental and other theoretical data.

Research highlights▶ The present paper investigated the structural, elastic and lattice dynamical properties of LuB2, LuB4, and LuB12 by means of first-principles calculation. ▶ The elastic constants and other mechanical parameters such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio of polycrystalline aggregates were studied, and the ductility and brittle were further discussed. ▶ Furthermore, the lattice dynamical properties were investigated for understanding the underlying mechanism of the structural stability and elastic properties.