Based upon large and relaxed grain boundary models in intergranular glassy film models in polycrystalline β-Si3N4, ab initio modeling and theoretical tensile experiments were carried out for both clean and Y-doped models. It was shown that the increased covalent bonding between Y and O or N through the participation of the Y-4d and Y-3p orbitals was the mechanism by which Y-ions enhanced the mechanical and elastic properties of the Y-doped grain boundary and intergranular glassy film models. For the intergranular glassy film models, the distribution patterns of Y-ions in the glassy region were investigated by using total energy calculations. The Y-ions preferred to be at the interfacial region between the intergranular glassy film and the bulk crystal. Defect-like states of various origin could be identified near to the valence band and the conduction band edges. Such theoretical predictions, obtained from calculations of the fundamental electronic structures of materials could be used to derive the local strain fields of dissimilar particles that could be linked to continuum-level theories via finite element methods.

Ab initio Modeling of Clean and Y-Doped Grain Boundaries in Alumina and Intergranular Glassy Films (IGF) in β-Si3N4. W.Y.Ching, J.Chen, P.Rulis, L.Ouyang, A.Misra: Journal of Materials Science, 2006, 41[16], 5061-7