First-principles prediction of mechanical properties of gamma-boron

The structural and mechanical properties of γ -B₂₈ are investigated using first-principles density functional calculations. The single-crystal elastic constants calculations show that γ -B₂₈ is mechanically stable under ambient conditions. The predicted bulk and shear moduli of γ -B₂₈ are comparable to those of boron suboxide, suggesting that γ -B₂₈ can be a superhard material. We also obtained the ideal tensile strength for γ -B₂₈ through deformation from the elastic regime to structural instability. We find that the breaking of B1-B1 and B1-B2 bonds is responsible for the failure of γ -B₂₈ under 〈 100 〉 and 〈 010 〉 tensile deformation, respectively.