Exploring Ferroelectric Vortex Topology and morphotropic Phase Boundaries by Phase Field Method

The perovskite crystal structure determines the appearance of ferroelectricity and the determination of the polarization direction of ferroelectric ceramics. When the polarization direction has a certain order, different domain structures will combine to form a multiparticle system with a specific morphology, the topological structures that exist in ferroelectrics. In this study, the domain structure of potassium sodium niobate (K0.5Na0.5NbO3) thin films under different hysteresis electric fields and thicknesses was observed by the phase field method. According to the different switching paths of the domain structure under the electric field, the domain is divided into fast and slow switching process. Based on this, a method is proposed to first determine the domain switching state of the desired experiment and then conduct directional observation. Through the analysis of the domain structures combined with the polarization vector, a clear multi-domain combined vortex-antivortex pair topological structure was observed for the first time in K0.5Na0.5NbO3 films. The vortex structure was further analyzed for its switching process, and it was observed that this vortex topological microstructure can make the domain more likely to switch, so that more small-scale polarization vectors can be ordered to form the desired multiparticle system topology. This polarization vector ordering is similar to the microscopic phase boundary formed by the specific polarization directions on both sides of the morphotropic phase boundary (MPB) for the improvement of the dielectric properties of ferroelectric materials.