First-principle study on the structural, elastic and electronic properties of CrB4 hard material under different pressures

The crystal structures, elastic, mechanical and electronic properties of Pnnm-CrB4 crystal are explored using the first-principles calculation. The lattice constant, elastic constants, bulk modulus are calculated under different pressures. Phonon dispersion and elastic constant calculations show that Pnnm-CrB4 is thermodynamically and mechanically stable at standard pressure. The structural analysis shows that the pressure has different effect for the three axes, and c-axis is the most compressible and b-axis is the least compressible, which is consistent with the analysis of the bulk moduli along a-, b-, and c-axis. In addition, CrB4 behaves in a brittle manner within the given pressure range and the analysis of the Poisson's ratios indicates that CrB4 is a covalent material. Band structure, electron local function and density of states are also calculated. And the results show that no band gap exists in the band structure and CrB4 has the metallic character, which is consistent with the result of density of state.