Polarization in epitaxial LaFeO$_{3}$/SrFeO$_{3}$ superlattice thin films*

Controlling ferroelectricity in perovskite thin-films requires an understanding of the many factors that are known to affect their polar behavior, such as octahedral rotations, cation ordering, oxygen vacancies, and the surface and interface terminations. Here, we report a study using a combination of aberration-corrected scanning transmission electron microscopy, electron-energy loss spectroscopy (EELS), and density functional calculations (DFT) to demonstrate how these factors work in concert to give rise to polarization in LaFeO$_{3}$/SrFeO$_{3}$ superlattices grown on SrTiO$_{3}$ substrates. Although both LaFeO$_{3}$ and SrFeO$_{3}$ are non-polar in the bulk, microscopy results show Fe-displacements in the superlattices indicating a dipole-like electric field. The magnitude of the observed displacements peaks in the interior of the films and goes to zero towards the substrate and the surface. O K EELS results show variation in intensities within the films, suggesting that oxygen vacancies may play a role. DFT results explaining the origin of the observed polar displacements within the superlattices and the effect of the abovementioned factors will be presented.