Atomistic structure of calcium silicate intergranular films between prism and Basal planes in silicon nitride: A molecular dynamics study

Molecular dynamics simulations of approximately 15 Å thick intergranular films (IGFs) containing SiO2 and CaO in contact with two surface terminations of the prism (10^̄ 10) and basal planes (0001) of Si3N4 were performed using a multibody interatomic potential. Samples with the same composition (1.5 mol% CaO) and number of atoms but different crystal planes (i.e., the prism and basal planes of Si3N4) were studied. In both the prism and basal cases, the IGF in the final configuration is well-ordered in the interface region. A small number of N ions from the crystal moved into the IGF near the interface, and O ions moved into the N sites in the crystal, indicating the formation of a Si-O-N interface. In addition, Ca ions do not segregate to the IGF-crystal interface. The bonding characteristics of the O ions at the interface with neighbor Si ions are different in the prism and basal cases. Such difference may be explained by the difference in the two crystal Si3N4 surfaces. The Si-O bond length of the IGF has a range from 1.62 Å to 1.64 Å, consistent with recent experimental findings.