Exaggerated grain growth in Ni-doped BaTiO3 ceramics

With approximately 0.7 mol% Ni doping, the formation of hexagonal phase in BaTiO3 after sintering at a temperature above 1385 °C in air has been observed. The shape of the h-BaTiO3 grains is plate-like, and the length of these h-BaTiO3 plates can be longer than 15 mm. As the amount of Ni doping increases above or decreases below 0.7 mol%, the hexagonal phase disappears and the resulting microstructure is dominated by small BaTiO3 grains. This critical amount of Ni (i.e. 0.7 mol%) corresponds to the solubility of Ni in BaTiO3. The exaggerated growth of the plate-like grains in BaTiO3 relates strongly to the formation of oxygen vacancies due to the presence of Ni acceptors.