Atomic-Scale Interplay between Antiphase Boundaries and Charged Domain Walls in Epitaxial BiFeO3/KTaO3 Systems

Oxide interfaces, characterized by the interplay of dissimilar lattices, orbitals, charges, and spins, exhibit a wealth of emergent phenomena, such as superconductivity, two-dimensional electron gases, and magnetoelectric coupling, which hold great promise for next-generation integrated functional devices. Here, we demonstrate the formation of antiphase boundaries (APBs) near a BiFeO3/KTaO3 interface prepared by pulsed laser deposition, which further alters the local polarization features and promotes the formation of charged domain walls in BiFeO3. Using high-angle annular dark-field scanning transmission electron microscopy combined with atomic-resolution energy-dispersive X-ray spectroscopy, the atomic structures and chemical compositions of these APBs were elucidated, featuring both planar and stepped configurations. High-temperature pretreatment of KTaO3 substrate facilitates a formation of controlled depletion of K+ ions at the surface, which further drives the diffusion of Bi3+ into the substrate and helps the nucleation and stabilization of APBs. Furthermore, the built-in electric field generated by these charged APBs profoundly alters the local polarization, inducing the formation of charged domain walls above the APBs. Our findings not only reveal a mechanism for creating APB configurations under defined conditions but also offer insights into how interfacial chemistry can be leveraged to manipulate microstructures.