Determination of the Type of Ferroelectric Domain Nucleated around the Dislocation by the Mechanism of Domain Wall Nucleation

According to the elastic theory of dislocations, the stresses in the region surrounding the core of the dislocation can be relieved if we give a small hypothetical displacement, called the relieving displacement, to the atoms in this region. This concept has been developed to show that nucleation of a suitable domain region is favoured around a dislocation, while the actual nucleation takes place under the influence of the suitably applied external dc electric field. There are several equivalent directions possible for the polar axis, and the relieving displacement can decide which one of these is to be preferred for the domain region to be nucleated around the dislocation. The approach is illustrated with reference to the case of KNbO3 where the mechanism of domain formation is that of domain wall nucleation. It is shown that the effect of having a suitable domain around the dislocation is to reduce the strain energy of the dislocation. The domain width has been calculated, and it is found to be agreeing with the earlier observed experimental values.