This paper reports recent theoretical perspectives and experimental results on microstructural evolution during sintering in terms of the interface structure, which is either rough (atomically disordered) or faceted (atomically ordered). The paper presents theoretical predictions and calculations of grain growth during liquid‐phase sintering based on crystal growth theories. It is shown that various types of grain growth behavior, which may be normal, abnormal, or stagnant, can appear as a result of the coupling effects of the maximum driving force for growth and the critical driving force for appreciable growth. The predictions are also shown to be valid in the case of solid‐state sintering. A number of experimental observations showing the effect of some critical processing parameters have been found to be in excellent agreement with the predictions. Principles of microstructure development (grain growth control) during sintering are suggested. In addition, the effect of the interface structure on densification is briefly described and discussed.

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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.