Diffusion induced grain-boundary migration and enhanced grain growth in BaTiO3

The effect of diffusion induced grain-boundary migration (DIGM) on grain growth has been studied in a model system of BaTiO3-PbTiO3. When sintered BaTiO3 samples of two different grain sizes were heat-treated in contact with PbTiO3, DIGM occurred in the coarse-grained samples (similar to 200 mu m in average size) while fast grain growth was observed in the fine-grained samples (similar to 4 mu m). Energy dispersive spectroscopy (EDS) analysis confirmed that the fast growth of BaTiO3 grains was accompanied by the alloying of Pb and thus related to DIGM. A calculation of coherency strain energy for the BaTiO3-PbTiO3 system showed that the coherency strain energy of a coherent (Ba0.8Pb0.2)TiO3 layer on BaTiO3 was between 2 and 3 MJ/m(3) depending on the surface orientation. The calculated coherency strain energy values are much higher than the capillary energy due to the grain boundary curvature of 4 mu m grains in the fine-grained sample. The observed enhancement of grain growth appears therefore to be a result of DIGM. Such grain growth enhancement by DIGM is thought to occur in materials processing under chemical inhomogeneity or inequilibrium, for example, in the sintering of powder mixtures and in the annealing of chemically inhomogeneous polycrystals.