Anomalous grain growth in donor-doped barium titanate with excess barium oxide

Grain growth and semiconductivity of donor-doped BaTiO3 ceramics with an excess of BaO and additions of SiO2 or B2O3 were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO2 or B2O3, exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO3 seed grains were embedded in a sample of donor-doped BaTiO3 with an excess of BaO (without SiO2 or B2O3), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO3 and not NGG.