Molecular dynamics simulation of an intergranular glass phase in alumina based ceramics

Molecular dynamics simulations were performed to study grain boundaries of α-alumina (Al₂O₃) with a glassy phase of anorthite (CaAl₂Si₂O₈). We calculated atomic structures and excess energies of the grain boundaries with different thicknesses of the glassy film. It was found that the grain boundary energies readily decreased with increasing film thickness, while increased for thicknesses of more than 2 nm. In other words, excess energies exhibit a minimum at a thickness around 1 nm. In this range of film thicknesses, the atoms in the glassy film show a short-range ordered structure and slow diffusion rather than the random structure and rapid diffusion expected for a liquid phase. These results are thought to correspond to an observation of an equilibrium thickness for intergranular glassy films in ceramics.