Inhibition of abnormal grain growth in BaTiO3 by addition of Al2O3

The effect of additions of up to 1 mol% Al2O3 on abnormal grain growth in BaTiO3 samples sintered at 1200 and 1250 °C has been studied. Samples with and without additions of 0.4 mol% TiO2 were prepared. For the samples without added TiO2, addition of 0.1 mol% Al2O3 increases the number density of abnormal grains, with further additions reducing the number density. The initial increase in number density is caused by Al2O3 forming a solid solution with BaTiO3 and releasing TiO2 to the grain boundaries. This excess TiO2 then reacts with BaTiO3 to form Ba6Ti17O40, which promotes {1 1 1} twin formation and abnormal grain growth. Further additions of Al2O3 react with BaTiO3, Ba6Ti17O40 and excess TiO2 to form Ba4Al2Ti10O27 and BaAl2O4 second phases, neither of which are growth sites for abnormal grains. For the samples with added TiO2, addition of Al2O3 decreases the number of abnormal grains due to the Al2O3 reacting with the excess TiO2 and BaTiO3 to form Ba4Al2Ti10O27 and BaAl2O4 instead of Ba6Ti17O40.