Nucleation and Growth of Ferroelectric Domains in BaTiO3 at Fields from 2 to 450 kV/cm

The nucleation and movement of 180° domain walls in BaTiO3 crystals with salt-water electrodes has been observed directly by partial switching and repeated differential etching at applied fields from 2 to 450 kV/cm. Most of the polarization was found to be reversed by sidewise growth of new domains at these fields, as it is at lower fields, but the sidewise wall velocities are higher, as high as 105 cm/sec. The nuclei are originally circular cylinders, becoming squared up by sidewise growth whose lowest velocity is along the 100 crystal axis. The sidewise wall velocity and the nucleation rate each vary as E1.4, thereby causing the known E−1.4 variation of ts. The nucleation rate dependence is not understood, but the wall-velocity dependence agrees strikingly with a previously uncalculated prediction of the Miller-Weinreich theory. This indicates that, at both high and low applied fields, the apparent sidewise motion of 180° domain walls is due to the nucleation and forward growth of knife-shaped steps on the previously existing wall.