Strain-engineered flexoelectricity and oxygen vacancy dynamics for modulating interfacial charge transport in BaTiO₃

Strain engineering has emerged as a powerful strategy for tailoring the ferroelectric properties and interfacial charge transport behaviors in complex oxide heterostructures. However, the underlying coupling mechanisms between strain-induced polarization reversal and defect-mediated barrier modulation remain in-depth understanding. In this study, controllable strain gradients are introduced through the use of intermediate layers to simultaneously manipulate the polarization orientation of BaTiO₃ thin films and modulate interfacial barrier properties. We systematically investigate the interplay among strain states, polarization behavior, and oxygen vacancy dynamics. Opposing strain states induce distinct polarization orientations in BaTiO₃, as confirmed by phase reversal and local hysteresis loops. Vacuum annealing is employed to tune the overall oxygen vacancy concentration, while flexoelectric field induced by strain gradient governs the migration and spatial distribution of vacancies. Compressive and tensile strains respectively drive oxygen vacancy accumulation near the surface or at the bottom interface, thereby modulating the Schottky barrier height and associated rectifying behavior. These results reveal a synergistic mechanism whereby flexoelectric polarization and strain-driven redistribution of oxygen vacancy cooperatively regulate charge transport in ferroelectric heterostructures.