DFT based comparative analysis of physical properties of binary metallic diborides XB2 (X = Cr, Mo and W)

Transition-metal borides (TMBs) have long attracted attention of the researchers because of their unique mechanical and electrical properties including superconductivity. We have explored the structural, mechanical, electronic, optical, and some thermophysical properties of XB 2 (X = Cr, Mo and W) binary metallic diborides in detail, employing density functional theory based first-principles method. Many of the physical properties, including direction-dependent mechanical properties, optical properties, and thermo-mechanical properties are being investigated for the first time. According to this study, XB 2 (X = Cr, Mo and W) compounds exhibit reasonably good machinability, delocalized metallic bonding, high Vickers hardness, and high Debye temperature. CrB 2 and MoB 2 exhibit brittleness whereas WB 2 shows ductility. The mechanical stability of XB 2 (X = Cr, Mo and W) compounds has been confirmed. Based on the calculated bulk modulus, Young’s modulus and shear modulus of XB 2 (X = Cr, Mo and W), these compounds can be regarded as potential candidates of ultra-incompressible and hard materials. The metallic nature of XB 2 (X = Cr, Mo and W) compounds is confirmed via electronic band structures with a high electronic energy density of states at the Fermi level. The optical parameters exhibit excellent agreement with the electronic properties. All optical constants show a considerable degree of anisotropy. The reflectivity spectra reveal that XB 2 (X = Cr, Mo and W) compounds are good reflectors in the infrared and near-visible regions. The compounds under study have high Debye temperature, melting temperature, lattice thermal conductivity, and minimum phonon thermal conductivity, which corresponds well to their elastic and bonding properties. The extremely high melting temperature of WB 2 indicates that WB 2 is a promising material for high-temperature applications. The superconducting state parameters of XB 2 (X = Cr, Mo and W) compounds are also investigated.