Flexoelectric Polarization Control via Defect‐Driven Strain Gradients in Complex Oxide Thin Films

ABSTRACT Electromechanical coupling in oxide thin films can be realized through strain‐gradient‐driven flexoelectricity, but the lack of directional control has hindered its practical implementation in devices. Here, we demonstrate that defect‐gradient engineering through spatial redistribution of oxygen vacancies provides a device‐compatible route to control flexoelectric polarization in single‐crystalline LaAlO ₃ (LAO) thin films. Vacancy‐rich lines patterned on the LAO surface induce local lattice expansion and converging strain gradients, which yield a pronounced in‐plane electromechanical response as revealed by lateral piezoresponse force microscopy. Remarkably, when the spacing between vacancy‐rich patterns is reduced below ∼100 nm, the response evolves from alternating to unidirectional, ultimately producing uniform in‐plane poling. Finite‐difference drift‐diffusion and Poisson simulations corroborate that asymmetric defect distributions drive a robust in‐plane electromechanical response. This electrically writable defect‐gradient strategy enables deterministic modulation of flexoelectric polarization at microscopic and mesoscopic scales, without mechanical deformation, opening pathways to defect‐gradient‐based functionalities in rewritable oxide electronics, nanoscale sensing, actuation, and energy harvesting.