Unusual phase transition mechanism induced by shear strain in Si2BN planar structures and comparison with graphene: an ab initio DFT study

Using ab initio methods we show that by applying shear strain, a phase transition occurs between the AB and the AA Si₂BN planar sheets. Si–Si bonds stretch and bend towards the strain direction, causing an internal displacement of the remaining almost unchanged Si₂BN strips. As the shear strain increases, Si–Si bonds weaken and break, while leading to new Si–Si bond formation and causing the phase transition. The planar structure is maintained throughout the application of the strain, with no buckling, a phenomenon not reported so far in other 2D materials. Performing the same calculations for graphene we show that its structural deformations are strikingly different and result in buckling.