The variation of oxygen and cation vacancies in strontium titanate polycrystals flash-sintered under direct and alternating electric fields

Point defect formation was investigated based on the electron energy-loss near-edge structure observed within the grains and 10 nm from the grain boundaries of strontium titanate flash-sintered under direct (DC) and alternating (AC) electric fields with strengths of 100 and 200 V/cm. More oxygen vacancies were generated in both regions under the DC field than under no field, but the same behavior was only observed under the AC field of 200 V/cm. Similarly, strontium vacancies were generated in both regions under the DC field but only within the grains under the AC field. The discrepancies in vacancy formation may be related to their generation and annihilation rates at grain boundaries under AC electric fields. The intricacies of the electric field-induced vacancy formation mechanism require further elucidation, but this work underscores the importance of considering the roles of both oxygen and cation vacancies in the accelerated mass diffusion during flash sintering.