High-Temperature Resistance Anomaly at a Strontium Titanate Grain Boundary and Its Correlation with the Grain-Boundary Faceting–Defaceting Transition

With the development of nanotechnology, more attention and care should be paid to grain-boundary structure and its structural transition in order to understand the behavior of polycrystalline materials with grain sizes down to nanometer levels. Here, we report direct evidence suggesting a correlation between a grain-boundary structural transition and a change in the electrical property, using a strontium titanate (SrTiO3) bicrystalline grain boundary as a model system. The electrical properties of grain boundaries in SrTiO3 play a critical role in barrier-layer devices, such as capacitors and varistors. [1] It is believed that the electrical behavior depends on the double Schottky barrier established by the interface charge and the associated space charge across the grain boundary. [2–4] The interface charge arises from the segregation of point defects, which form because the energies to move anions and cations to the grain boundary are different. [5] The consequent electrostatic potential obstructs the transport of charge carriers across the grain boundary. For pure, undoped SrTiO3, Kim et al., [6] using electron energy loss spectrometry (EELS), showed that the ratio of Ti to O concentration in various boundaries is higher than in the bulk, indicating that the grain boundaries are enriched in Ti or deficient in O. Browning et al. [7] reported that a ∑5 grain boundary (∑ denotes the reciprocal of the fraction of common lattice points of the adjoining grains) is segregated by oxygen vacancies. Klie and Browning [8] reported the segregation of oxygen vacancies at a