Critical grain size for abnormal grain growth of BaTiO3 in air

Abstract

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%-TiO 2-added BaTiO3 powder compacts at 1250°C for 20 h in air. Additionally, plates with matrix grains having various grain sizes were prepared by sintering BaTiO3 powder compacts at 1300°C for 0.5, 2, 8 and 48 h in H2. Abnormal growth of the twin-containing large grains into matrix grains occurred for the matrix grain size of 4.1 μm and did not occur for that of 5.6 μm. It appears, therefore, that the critical size for abnormal grain growth is approximately 5 μm, which correspond to a critical driving force of 4.6 J/mol. The commonly observed abnormal grain growth during sintering of undoped BaTiO3s in air is, hence, understood to result from much higher driving forces of fine powders than the critical value.