Switching of KNbO3single crystals under steady electric field conditions

Switching studies on KNbO 3 single crystals were carried out under DC electric field conditions. The single crystals, both the major faces of which were photographed to note down the details of domain structure, were subjected to steady electric fields of known value and duration. The disturbances produced in the domain structure form part of the switching process. These changes were studied by photographing the faces immediately after the field was removed. It is found that switching proceeds through the nucleation of domain walls rather than the nucleation of fresh domains, and the lateral and longitudinal movement of domain walls. There exists a critical field of about 80 V cm -1 for nucleation. The walls are usually nucleated in pairs or in even numbers. The number of walls so nucleated for a given field applied for a given time depends upon the defect conditions of the crystal. As regards wall movements, it is found that the lateral wall velocities are comparable with forward/backward wall velocities. The 90 degrees and 60 degrees walls can be distinguished by their different way of movement. Thus the method provides a direct probe into the switching mechanism, revealing in the present case an important step in switching, viz. the nucleation of domain walls.