Nonlinear driving force–velocity relationship for the migration of faceted boundaries

A non-linear relationship between boundary migration and its driving force for faceted grain boundaries is demonstrated in a BaTiO3 model system using the solid-state single-crystal growth technique. BaTiO3 (0.4 mol.% TiO2) samples with different grain sizes were prepared by sintering powder compacts in H2 for various times. Single-crystal seeds with {1 0 0} and {2 1 0} orientations were joined to the sintered samples and annealed in air for various times up to 20 h. During the air annealing, the matrix grain size did not change, indicating that the driving force for the growth of the single-crystal seeds remained constant. Under driving forces that exceeded a critical value, the seed crystals grew into the polycrystals. The critical driving force was lower and the growth rate was ∼10 times higher for the {1 0 0} crystal compared with the {2 1 0} crystal. These results demonstrate the presence of a critical driving force for the migration of a faceted boundary and the remarkable effect of the crystallographic orientation on the boundary migration. The observed nonlinear migration behavior of faceted boundaries is similar to that of faceted solid/liquid interfaces.