Interferometric study of domain structure in barium titanate

Abstract

The surface microtopography arising out of the 90° domain walls in single crystals of Barium titanate in the ferroelectric tetragonal state has been studied in detail employing optical and multiple beam interferometric techniques. The domain walls mark a change in level at the crystal surface and it is shown that the change in level is proportional to the distance between the domain walls. A step ladder structure is often found on the crystal surface which indicates, beyond doubt, the head to tail coupling of the dipoles. In a few cases, however, 90° wall configuration with head to head or tail to tail orientation has been observed. These laminae frequently advance in groups in the two perpendicular directions parallel to the edges of the crystal. As a result of the intersection of these groups the crystal surface becomes highly complicated with a step ladder structure in mutually perpendicular directions, terminating in a square base or at times in a point. In many cases, the multiple beam interferometric techniques have shown that the crystal surface is deformed with a cylindrical curvature: the axis of a cylinder being parallel to the edge of the crystal. Some times one observes the crystal having cylindrical curvatures in perpendicular directions.