Mechanical and electronic properties of superhardReB2

Abstract

Considering the effect of spin-orbit coupling, we have studied the equation of state, elastic properties, and the electronic structures of $\mathrm{Re}{\mathrm{B}}_2$ by first-principles plane-wave basis pseudopotential calculations. Our calculated results show that $\mathrm{Re}{\mathrm{B}}_2$ has high bulk modulus $\left(356\mathrm{GPa}\right)$, large shear modulus $\left(293\mathrm{GPa}\right)$, and great elastic constant $c_{44}$ $\left(284\mathrm{GPa}\right)$, and thus support that $\mathrm{Re}{\mathrm{B}}_2$ is ultraincompressible and a potentially superhard material. Besides the compact crystal structure, the electronic mechanisms of its hardness can be understood from the highly directional covalent bonds and the optimal filling of the bonding states.