Critical grain size for abnormal grain growth of BaTiO3 in air

The critical average size of matrix BaTiO3 grains for {111} twin-assisted abnormal grain growth in air was determined through the use of bi-layer samples of large BaTiO3 grains with {111} twin lamellae and fine matrix grains of various sizes. Plates with large BaTiO3 grains containing {111} twin lamellae were prepared by sintering 0.4 mol%-TiO2-added BaTiO3 powder compacts at 1250 degrees C for 20 It in air. Additionally, plates with matrix grains having various grain sizes were prepared by sintering BaTiO3 powder compacts at 1300 degrees C for 0.5, 2, 8 and 48 h in H-2. Abnormal growth of the twin-containing large grains into matrix grains occurred for the matrix grain size of 4.1 mu m and did not occur for that of 5.6 mu m. It appears, therefore, that the critical size for abnormal grain growth is approximately 5 mu m, which correspond to a critical driving force of 4.6 J/mol. The commonly observed abnormal grain growth during sintering of undoped BaTiO3 in air is, hence, understood to result from much higher driving forces of fine powders than the critical value.