Migration enhancement of faceted boundaries by dislocation

Abstract

To observe the effects of dislocation density and crystal plane orientation on the migration of faceted boundaries, bi-layer BaTiO 3 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.

Growth of single crystalline seeds into polycrystalline strontium titanate: Anisotropy of the mobility, intrinsic drag effects and kinetic shape of grain boundaries

“…This is in contrast to barium titanate, where the polycrystalline matrix grains underlie P crit and hence do not grow [30,32,59]; at the same time single crystalline seeds can overcome P crit due to their higher driving force and grow rapidly [30,32,33]. In the present results both single crystals and polycrystals grow (certainly at very different mobilities).…”

“…(9)the single crystal still grows due to its higher driving force. This is the case for barium titanate [30,32,33], but not for strontium titanate. The cause of this behavior is not clear from the present experiments.…”

“…The experiment of a single crystal joined to a polycrystal was conducted for barium titanate as well [30,32,33]; however the polycrystalline matrix did not show grain growth, while the single crystal grows considerably. As shown in Fig.…”

“…Experiments in this geometry have been used for more than three decades in measuring growth rate anisotropy in ceramics, e.g. Alumina [22][23][24][25][26][27][28][29], Barium titanate [30][31][32][33] and Strontium titanate [34][35][36]. In some of these previous experiments and in this paper, measurements of the mean migration distance of different single crystal orientations into the polycrystalline matrix and of the matrix grain size as a function of time, temperature, and single crystal surface orientation are obtained.…”

Solid‐State Conversion of Single Crystals: The Principle and the State‐of‐the‐Art

“…It is, therefore, necessary to control the grain growth in the polycrystal. Apart from the conventional mechanisms of AGG, all of which are based on the diffusion control of boundary migration, a structure‐dependent migration mechanism of grain boundary, the so‐called mixed control mechanism, was proposed recently, on the basis of experimental observations of grain growth as well as single crystal growth behavior . This mechanism can explain the occurrence of various types of grain growth behavior in polycrystals and provides the groundwork for the discovery of the general principle of microstructural evolution …”