Switching of KNbO₃single crystals under steady electric field conditions

Abstract

Switching studies on KNbO3 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.

Electric field induced domain rearrangement in potassium niobate thin films studied by in situ second harmonic generation measurements

“…In addition they observed a local curvature of the domain wall near the stress fields of a dislocation. Ingle and Kokate 19 and Kulkarni et al 20 also reported bending of 60°domain walls in KNbO 3 near stress fields of dislocations. Mishra and Ingle 17 observed that 60°walls in KNbO 3 lineup in pairs on either side of a dislocation array that was formed due to impurity atoms.…”

A dislocation model for nucleation of domain walls in KNbO3single crystals

“…It was reported earlier (Ingle and Kokate 1983) that switching by a steady electric field proceeds in single crystals of KNbO3 through the nucleation of domain walls rather than the nucleation of domains. There exists a critical field of -8 X lo3 V m-1 for nucleation.…”

“…The model is based on the experimental observation earlier (Mishra andIngle 1974, Ingle andBangre 1978) that 60" domains in KNb03 almost always contain dislocation loops along the central regions and have significant influence on the domain structures in crystals. Again it was found that under the influence of the DC electric field, a pair of domain walls by the sides of the loops can be nucleated, if not existing already (Ingle and Kokate 1983). It is natural to infer that these dislocation loops play a significant role in bringing about the nucleation of the walls.…”

The conductance analysis of ferroelectric KNbO3single crystal

“…KNbO, is an important ferroelectric material with various nonlinear optical and electro-optical applications [??;I. The polarization reversal process has been studied by switching carried out under steady electric field conditions [4,5]. Due to the large spontaneous polariiation and the high packing densib of octahedral in its structure, the Downloaded by [Umeå University Library] at 14:00 18 November 2014 132 C .…”