Origin of the rigidity in tetragonal MB (M = Cr, Mo and W) and softening of defective WB: First-principles investigations

First-principles calculations were performed to understand the underlying origin of the rigidity of metal monoborides and effects of defects and impurities on the mechanical properties of tungsten mono-boride. A strong covalent bonding caused by a zig-zag structural topology is responsible for improving mechanical properties of monoborides. The occurrences of vacancies or impurities weaken the average bond strength, resulting in the mechanical properties degradation consequently, which demonstrated by electronic structure and charge density distributions.