Electric current‐controlled synthesis of BaTiO 3

In BaTiO 3 , flash‐sintering associated with a surge of the specimen electric current sometimes results in an inhomogeneous microstructure including Ti‐excess secondary phases because of discharging. We applied field‐assisted sintering technique ( FAST ) under precisely controlled specimen current that was set just below the threshold value for the occurrence of flash event for BaTiO 3 , to avoid the occurrence of the discharging. As a result, uniform and fine‐grained compacts were obtained without any secondary phases. A relative density of approximately 92% was achieved under FAST condition of 100 V/cm with a limiting current of 72 mA and soaking time of 3 hours at 1070°C. The voltages during sintering under a constant current of 72 mA were found to decrease during the soaking process. Electron energy loss spectroscopy revealed the generation of excess oxygen vacancies at/near grain boundaries. The excess oxygen vacancies induced by application of DC electric fields were confirmed to reduce the voltages and to retard the shrinkage rate in a final sintering stage.