Molecular dynamics simulations of the atomistic structure of the intergranular film between silicon nitride grains: Effect of composition, thickness, and surface vacancies

Molecular dynamics computer simulations were used to study the atomistic structure of intergranular films (IGFs) between two basal oriented Si3N4 crystals or between combined basal and prism oriented crystals. Ordering of the ions into the IGF induced by the crystal surfaces was observed using density profiles of the ions, although that ordering is effected by the roughness of the crystal surface. Density profiles of the sum of all ions misleadingly shows a rapid decay in the density oscillations and apparent ordering into the IGF. However, this is an artifact of the coincidence of the maximum in the peaks of one species with the minimum of another species and the actual oscillations of individual species extend into the IGF farther than the sum profile indicates. This result would have important implications regarding the density oscillations observed in physical experiments with regard to the actual extent of ordering into the IGF induced by the crystal surface.