Enhancement of Interfacial Polarization in BaTiO3 Thin Films via Oxygen Inhomogeneity

Enhancement of interfacial ferroelectricity is crucial for the development of nanoscale ferroelectric devices, such high density and nonvolatile memory. Although the epitaxial strain can lead to improved properties, the limited choices of substrates and strain relaxation have hindered the further tuning of ferroelectricity by strain engineering. To overcome this limitation, the interaction between polarization and defects is regarded as a potential route to enhance the interfacial polarization. Here, a universal method to achieve a polarization-enhanced interface by tuning the distribution of oxygen in lead-free BaTiO3 films is demonstrated. The interfacial phase processes largely increased c-axis lattice constant, tetragonality, and about 100% increasement of Ti atom displacement near interface within thickness of 8 unit cells, suggesting enhancement of spontaneous polarization up to 70 mu C cm(-2). The gradient distribution of oxygen along c-axis is also revealed. In addition, the first-principle Monte Carlo simulation of the tetragonality and polarization support the experimental results. It is suggested that the inhomogeneity of oxygen and interfacial charges could induce an electric field and further enhance the interfacial polarization. This work provides a new route of utilizing the oxygen distribution to engineer the ferroelectrics and paves the way for the development of nanoscale ferroelectric devices.