Kinetic roughening of a Σ5 tilt grain boundary in SrTiO3

The grain boundary kinetics of a SrTiO3 bicrystal with a misorientation relationship of 36.8°/[1 0 0] (Σ5) is examined at elevated temperatures by in situ high-resolution transmission electron microscopy. At 973 K, the grain boundary migrates by the propagation of atomic steps with a height of half a unit cell (∼0.2 nm), but at 1173 K, it becomes rough and advances without the requirement of steps. All the temperatures examined are below the thermal roughening transition temperature of the grain boundary. These results give a clear indication of grain boundary kinetic roughening. We suggest that our present results may lead to the development of a unifying framework for previously suggested grain boundary migration mechanisms.