Stress relaxation study of ferroelectric domains

Abstract

In ferroelectric crystals the motion of twin domains associated with shape changes (such as the 90° domains in BaTiO₃ and the 60° domains in KNbO₃) can be studied by following the mechanical strain changes due to their movements. It is realized that the time dependent changes associated with such movements can be conveniently followed using the stress relaxation method. This method consists of deforming the crystal in a testing machine to any predetermined strain value and arresting the cross head of the machine when the load relaxes with time. The decrease in load is a consequence of the deformation of the crystal associated with the movement of the domains. Studies carried out at room temperature on BaTiO₃ and KNbO₃ single crystals using this method, gave the following results. Stress relaxation takes place only in a limited region of the strain. The relaxation rate shows a maximum in this region. The initial domain structure and strain rate are found to influence the rate of stress relaxation. These studies are of importance in understanding the kinetics of ageing behaviour in these crystals.