Grain growth in strontium titanate in electric fields: The impact of space-charge on the grain-boundary mobility

This study investigates grain growth in the perovskite oxide strontium titanate in an electric field. The seeded polycrystal technique was chosen as it provides a sensitive and controlled setup to evaluate the impact of different parameters on grain growth due to the well-defined driving force for grain growth. Current blocking electrodes were used to prevent Joule heating. The results show faster grain growth, and thus, higher grain-boundary mobility at the negative electrode. It is argued that the electric field causes point-defect redistribution, resulting in a higher oxygen vacancy concentration at the negative electrode. The local oxygen vacancy concentration is suggested to affect the space-charge potential at the grain boundaries. A thermodynamic treatment of the grain-boundary potential at a grain boundary without field shows that for a high oxygen vacancy concentration less space-charge and less accumulation of cationic defects to the boundary occurs. Therefore, at the negative electrode, a higher oxygen vacancy concentration results in less space-charge and less accumulation of cationic defects. The lower degree of defect accumulation requires less diffusion of segregated defects during grain-boundary migration, so that at the negative electrode faster grain growth is expected, as found in the experiments.