Observation of Hidden Polar Phases and Flux Closure Domain Topology in Bi2WO6 Thin Films

Topological textures of ferroelectric polarizations have promise as alternative devices for future information technology. A polarization rotation inevitably deviates from the stable orientation in axial ferroelectrics, but local energy losses compromise the global symmetry, resulting in a distorted shape of the topological vortex or inhibiting the vortex. Easy planar isotropy helps to promote rotating structures and, accordingly, to facilitate access to nontrivial textures. Here, we investigate the domain structure of an epitaxial thin film of bismuth tungsten oxide (Bi2WO6) grown on a (001) SrTiO3 substrate. By using angle resolved piezoresponse force microscopy and scanning transmission electron microscopy, we find the existence of a hidden phase with (100)-oriented ferroelectric polarizations in the middle of the four variant (110)-oriented polarization domains, which assists in the formation of flux closure domains. The results suggest that this material is one step closer to becoming an isotropic twodimensional polar material.

Automated summary

Topological textures of ferroelectric polarizations have potential applications in future information technology. However, energy losses and deviations from stability can affect the symmetry and shape of these textures. In this study, we investigated the domain structure of bismuth tungsten oxide thin films grown on SrTiO3 substrates using advanced microscopy techniques. We discovered a hidden phase with a different polarization orientation that promotes the formation of flux closure domains, bringing us one step closer to an isotropic two-dimensional polar material.