Asymmetric Ferroelectric Flux-Non-Closure Domain Enabling Giant Polarizations Through Local Lattice-Defect-Induced Antiphase Boundary in Polycrystalline BiFeO₃.

Abstract

The discovery of complex polar topologies in nanoscale ferroelectric superlattices has greatly enriched the ferroelectric topological domains. These domains, although different and intricate in their formats, origin, and strengths, generally arise from the intricate interplay between collective polarization behaviors and certain mechanical boundary conditions, for example, interfacial strains within ferroelectric superlattices. As most extensive prototype materials afford multiple functions, ceramics and/or polycrystalline films, hardly present polar topologies, and even become unreachable when the significantly enhanced polarizations are achieved simultaneously. Herein, we demonstrate the formation of a new ferroelectric topological domain, a polarization-asymmetric flux-non-closure domain (much close to vortex pattern), in polycrystalline BiFeO₃. This asymmetric ferroelectric topology, subjected to a driving force associated with local lattice defects, induces an antiphase boundary that relaxes the anisotropic lattice strains and structural distortion, resulting in greatly increased B-site Fe displacements and FeO₆ rotation angles. The formation of abundant asymmetric flux-non-closure domains also creates large net polarizations that are responsible for the significantly enhanced ferroelectric polarizations, up to 165.6 µC cm^-2. Our findings provide a broader platform for modulating ferroelectric flux-non-closure patterns in extensive polycrystalline materials through facile lattice defect engineering to achieve optimized ferroelectric properties and new topological states.