Mechanical properties and atomistic deformation mechanism of spinel-type BeP2N4

The anisotropic mechanical properties and atomistic deformation mechanism of incompressible γ-BeP2N4 were comprehensively investigated by first-principles calculations. According to the dependence of the Young’s modulus on different directions in crystal, the γ-BeP2N4 exhibits a well-pronounced anisotropy which may impose certain limitations and restrictions on its applications. The ideal strength calculations demonstrated that γ-BeP2N4 shows substantially lower ideal shear strength than superhard c-BN and diamond, suggesting that it cannot be intrinsically superhard as claimed in the previous studies. Furthermore, the origin of the lattice instability of γ-BeP2N4 under large shear strain that occurs at the atomic level during plastic deformation can be attributed to the breaking of P–N bonds in PN6 octahedrons.