Phase stability, physical properties of rhenium diboride under high pressure and the effect of metallic bonding on its hardness

Using first-principles calculations, the elastic constants, thermodynamic property and structural phase transition of rhenium diboride under pressure are investigated by means of the pseudopotential plane-waves method, as well as the effect of metallic bond on its hardness. Eight candidate structures of known transition-metal compounds are chosen to probe for rhenium diboride ReB2. The calculated lattice parameters are consistent with the experimental and theoretical values. Based on the third order Birch-Murnaghan equation of states, the transition pressure Pt between the ReB2-ReB2 and MoB2-ReB2 phases is firstly determinate. Elastic constants, shear modulus, Young's modulus, Poisson's ratio and Debye temperature are derived. The single-bonded B-B feather remains in ReB2 compounds. Furthermore, according to Mulliken overlap population analysis, a semiempirical method to evaluate the hardness of multicomponent crystals with partial metallic bond is presented. Both strong covalency and a zigzag topology of interconnected bonds underlie the ultraincompressibilities. In addition, the superior performance and large hardness (39.1 GPa) of ReB2-ReB2 indicate that it is a superhard material.