Abnormal grain growth and intergranular amorphous film formation in BaTiO3

Abstract

The effect of abnormal grain growth on the formation of amorphous films at grains boundaries was studied in a model system BaTiO3. 0.4 mol% TiO2-excess BaTiO3 powder compacts were sintered at 1380 degrees C for various times up to 16 h. During the sintering, abnormal grains formed. With the growth of the abnormal grains, amorphous films formed and eventually thickened up to 19.2 nm at grain boundaries. The film formation is attributed to the accumulation of Ti solutes at grain boundaries with the grain growth, while the film thickening is mostly caused by the redistribution of liquid at triple junctions. Extended annealing of the 16-h-sintered sample at 1350 degrees C for 15 days resulted in a thinning of the film to nearly 1.7 nm without a change in the grain size, showing an equilibrium thickness. This result demonstrates that the film thickness observed during the growth of the grain may not be the equilibrium thickness. The result further suggests that the shape of the abnormal grains, even when equiaxed, can differ from the equilibrium shape.