The mechanism of grain boundary motion in SrTiO3

General high-angle grain boundaries in polycrystalline SrTiO3 and boundaries between single crystals of SrTiO3 diffusion bonded to polycrystalline SrTiO3 were studied using high-resolution transmission electron microscopy. Nanometer length-scale steps were experimentally detected at grain boundaries and were correlated to the grain growth mechanism, meaning that grain boundary motion occurs by the movement of steps along grain boundaries. While it is common to consider grain boundaries as disordered areas, well-ordered and stepped boundaries were found in samples annealed at different temperatures, cooled to room temperature using different cooling rates, and in samples annealed under both reducing and oxidizing atmospheres. Specific types of steps were present at the studied boundaries annealed under an oxidizing atmosphere, indicating that the step energy in SrTiO3 is anisotropic. This behavior was consistent even under conditions in which a significant change in the grain boundary mobility was measured, indicating that even when the kinetics change, the mechanism associated with grain boundary motion remains the same.