Pressure Driven Enhancement of Ideal Shear Strength in bc8-Carbon and Diamond

Superhard materials with strong covalent 3D networks have been the focus of intense research over the past decades. In the current work, the ideal shear strength and deformation mechanism at ambient and high pressure for bc8-carbon (bc8-C) and diamond are systematically investigated by first-principles calculation. Our results demonstrate that the ideal shear strength of the bc8-C phase is much lower than that of diamond at ambient pressure. By introducing pressure effect, the ideal shear strength in both bc8-C and diamond increases with increasing pressure. Interestingly, the ideal shear strength for bc8-C exceeds that of diamond above 200 GPa due to the restriction effect by pressure. We have examined the origin of this phenomenon in terms of energy, volume, bond length, local bond deformation, and breaking mechanisms.