Oxygen-Vacancy-Engineered Robust Ferroelectricity in Epitaxial-Strain-Free SrTiO3 Films

SrTiO3 (STO), a typical quantum paraelectric material, has been extensively investigated for the stabilization of ferroelectric order through external perturbations. However, conventional approaches typically rely on epitaxial strain or external field excitation, limiting their suitability for epitaxial-strain-free and low-stress device architectures. Here, we demonstrate an epitaxial-strain-independent route to robust ferroelectricity in STO enabled by interfacial oxygen-vacancy engineering. By introducing a La0.5Sr0.5MnO3 (LSMO) bottom electrode with strong oxygen affinity, interfacial oxygen redistribution is promoted during epitaxial growth, resulting in significant oxygen-vacancy accumulation in the adjacent STO layer. The engineered oxygen vacancies drive local symmetry breaking and stabilize polar nanoregions in fully relaxed STO epitaxial films. Consequently, STO grown on the LSMO buffer layer exhibits robust room-temperature ferroelectricity with a remanent polarization of 14 μC/cm2, achieved without conventional epitaxial strain engineering. These findings establish interfacial oxygen-vacancy engineering as a viable strategy for inducing ferroelectricity in STO-based heterostructures and provide a possible route for designing emergent functionalities.