Structural properties and tensile deformation mechanism of amorphous Si3B3N7: Insights from molecular dynamics simulations

We conducted molecular dynamics simulations to study an amorphous model of Si ₃B ₃N ₇. The model consists of SiN _x ( x = 3, 4, and 5) and BN _y ( y = 2, 3, and 4) units, with 93.50% SiN ₄ and 99.13% BN ₃, forming a network structure. The splitting of the first peak of the g S i − S i ( r ) is caused by corner- and edge-sharing bonds, while N atoms belonging to NSi _m linkages or NB _n and NSi _pB _q linkages cause the first peak splitting of the g N − N ( r ) . The model includes Si-rich and B-rich regions, and three SiN, BN, and SiBN regions that can be identified through simplex analysis. Overlapping simplexes with R _S≥2.0 Å form a chain that spreads throughout the model. B atoms cause more large simplexes with R _S≥2.6 Å than Si atoms. We subjected the model to a uniaxial tensile test, which resulted in elastic and plastic deformations. Under tensile loading, the bond lengths of atoms belonging to large simplexes are stretched more than the rest. Si-N bonds are more easily broken than B-N bonds, indicating heterogeneous deformation. Large simplexes gather to form shear transformation zones, which evolve into shear band at strains above 0.143. The cluster of large simplexes grows in the shear band, causing crack propagation at high strains.