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

Abstract

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 two-dimensional polar material.

Three-Dimensional Visualization of Oxygen-Vacancy Migration and Redistribution in Ca-Substituted BiFeO3

“…Defect engineering of vacancies, antisite defects, interstitials, and chemical substitutions by donors/acceptors each provide a promising method for controlling local electronic properties and relevant electrochemical behaviors. − The cation redistribution of electrochemical modulation couples intrinsically to their physical properties, for example, in ferroelectrics, emerging enhanced conductivity at predefined domain walls, ultrafast ionic mobility, , chiral topology, and more. − The associated surface reaction kinetics are switched with electric polarization; furthermore, induced metastable states are considered as the signature of logical memory devices and superionic conductors . Thus, for materials with high ionic mobilities, an opportunity arises to carefully study the interplay between ionic motion and electric polarity (e.g., ferroelectric switching , ).…”