Migration enhancement of faceted boundaries by dislocation

To observe the effects of dislocation density and crystal plane orientation on the migration of faceted boundaries, bi-layer BaTiO3 samples composed of single crystals with different surface orientations and dislocation densities and polycrystals with different average grain sizes were annealed in air for 24 h. The migration distance was highly dependent on the crystallographic plane of the migrating boundary, consistent with our previous investigation. For large driving force, the migration distance appeared to be linearly proportional to the driving force for the studied range, irrespective of the dislocation density, suggesting diffusion-controlled migration. For driving forces lower than a critical value, which varied with the crystallographic plane of the single crystal, the boundary did not migrate. At a driving force between that for the linear region and that for no migration region, the migration of a crystal with a high dislocation density was faster than that of a crystal with a low dislocation density. These results show a migration enhancement of the boundary by dislocations, in contrast to the conventional understanding of the dislocation energy effect on the driving force for boundary migration. The observed dislocation effect is the first demonstration of dislocation-enhanced migration of faceted boundaries in single phase systems.