The structural correlation and mechanical properties in amorphous silicon nitride under densification

Molecular dynamics simulations of amorphous silicon nitride (a-Si3N4) with various densities ranging from 2.43 to 3.40 g cm− 3 were carried out to investigate their structural correlation and mechanical properties. The local structure was analyzed through the pair radial distribution functions, bond angle distributions and simplex statistics. The simulation reveals that although the fractions of structural units SiNx and NSiy strongly change with the density, the partial bond angle distributions of these structural units are identical for all constructed models. This result has enabled us to establish a relationship between the bond angle distributions and the fractions of structural units. Based on the analysis of simplex statistics, we found that all samples contain both the perfect and distorted tetrahedrons (SiN4). These perfect tetrahedrons (PTEs) may connect to each other via common nitrogen to create a large cluster- or poly-PTEs. The largest poly-PTE consists of 45.6% Si in the sample with a density of 3.02 g cm− 3 and 1.3% Si with the lowest density. We also found that even though at the high density the sample contains a remarkable number of voids in which the radius is larger than 1.1 Å. From uniaxial deformation of samples, the Youngʹs modulus, yield and flow stress were determined. The strain hardening and softening become more pronounced as density increases.