Low-compressibility and hard materialsReB2andWB2: Prediction from first-principles study

Abstract

First-principle calculations are performed to investigate the structural, elastic, and electronic properties of $\mathrm{Re}{\mathrm{B}}_2$ and $\mathrm{W}{\mathrm{B}}_2$. The calculated equilibrium structural parameters of $\mathrm{Re}{\mathrm{B}}_2$ are consistent with the available experimental data. The calculations indicate that $\mathrm{W}{\mathrm{B}}_2$ in the $P{6}_3∕mmc$ space group is more energetically stable under the ambient condition than in the $P6∕mmm$. Based on the calculated bulk modulus, shear modulus of polycrystalline aggregate, $\mathrm{Re}{\mathrm{B}}_2$ and $\mathrm{W}{\mathrm{B}}_2$ can be regarded as potential candidates of ultra-incompressible and hard materials. Furthermore, the elastic anisotropy is discussed by investigating the elastic stiffness constants. Density of states and electron density analysis unravel the covalent bonding between the transition metal atoms and the boron atoms as the driving force of the high bulk modulus and high shear modulus as well as small Poisson's ratio.