Microstructural and Mechanical Properties of Cubic Silicon Nitride: Insights from Molecular Dynamics Simulation

Molecular dynamics (MD) simulations have been used to study the mechanical behavior as well as the structural change of cubic (c-) Si3N4 upon uniaxial tensile loading. The Si3N4 sample is simulated under the cooling process and high pressure. At temperature of 300 K, most nitrogen (N) atoms arrange into fcc lattice, and the rest of N atoms have hcp and amorphous (a-) structures. The hcp and a- N atoms gather into a band. Upon uniaxial tensile tests, this c- Si3N4 exhibits elastic and plastic deformations. The fcc and hcp N atoms transform into a- N atoms under tensile loading. The band of a- structure develops and spreads across the sample with increasing strain. The transformation of SiNx units occurs from high to low coordination number in the a- structure. The large simplexes, with radii of 2.0 angstrom and above, grow and coalesce only in the a- structure during tensile loading, leading to form the porous structure. The formation of porous a- structure causes ductile deformation at high strain.