High-temperature resistance anomaly at a strontium titanate grain boundary and its correlation with the grain-boundary faceting-defaceting transition

The correlation between a grain-boundary structural transition and a change in the electrical property, using a strontium titanate bicrystalline grain boundary as a model system was investigated. Most grain-boundary structural transitions belong to faceting-defaceting transitions where an initially flat grain boundary is transformed into a faceted structure with a hill-and-valley shape. The bicrystal was annealed at 1600°C for 1 day and then cooled directly to 1100°C. The as-received bicrystal grain boundary and the annealed ones were imaged by using high-resolution transmission electron microscopy (HRTEM). The as-received bicrystal and those annealed in the temperature range from 1100 to 1500°C underwent faceting into the symmetric and asymmetric components. It was observed that the change in grain-boundary impedance, grain-boundary electronic structure, and the grain-boundary faceting-defaceting transition were closely related to each other.