Defect‐Mediated Polarization Stabilization Mechanism in Metal‐Ferroelectric Interfaces

Ferroelectric oxide heterostructures provide a versatile foundation for functional electronics, yet their performance is often hindered by the difficulty of manipulating domain states in ferroelectric films. Understanding the coupling between interfacial defects and polarization stability remains a central challenge for nanoscale ferroelectrics. This study investigates atomic‐scale mechanisms that influence the as‐grown polarization orientation in a BiFeO 3 /La 0.7 Sr 0.3 MnO 3 (BFO/LSMO) heterostructure. Utilizing piezoresponse force microscopy (PFM) and advanced aberration‐corrected STEM combined with energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and 4D‐STEM, we precisely mapped the polarization state and interfacial chemistry. A dual‐charge compensation mechanism is identified in which Sr cation diffusion into Bi vacancies is accompanied by the accumulation of oxygen vacancies at the interface. This synergistic mechanism promotes a strong built‐in field at the interface that electrostatically stabilizes the polar interface, leading to a large out‐of‐plane Fe displacement near the interface. Density functional theory (DFT) calculations further confirm that the Fe displacement increase is critically affected by the atomic plane positions of the oxygen vacancies relative to the diffused Sr atoms. The polarization remains robustly switchable under repeated cycling, demonstrating its viability for device operation. This work establishes atomic‐scale defect engineering as an effective strategy for stabilizing and manipulating domain states in ferroelectric thin films.