Oxygen-Vacancy-Induced Polar Behavior in (LaFeO3)2/(SrFeO3) Superlattices
- Oxygen-Vacancy-Induced Polar Behavior in (LaFeO3)2/(SrFeO3) Superlattices
- Rohan Mishra; Young-Min Kim; Juan Salafranca; 김성근; Seo Hyoung Chang; Anand Bhattacharya; Dillon D. Fong; Stephen J. Pennycook; Sokrates T. Pantelides; Albina Y. Borisevich
- Transition-metal oxides; multiferroics; polar oxides; DFT calculations; oxygen vacancies; scanning transmission electron microscopy
- Issue Date
- Nano letters
- VOL 14, NO 5, 2694-2701
- Complex oxides displaying ferroelectric and/or multiferroic behavior are of high fundamental and applied interest. In this work, we show that it is possible to achieve polar order in a superlattice made up of two nonpolar oxides by means of oxygen vacancy ordering. Using scanning transmission electron microscopy imaging, we show the polar displacement of magnetic Fe ions in a superlattice of (LaFeO3)2/(SrFeO3) grown on a SrTiO3 substrate. Using density functional theory calculations, we systematically study the effect of epitaxial strain, octahedral rotations, and surface terminations in the superlattice and find them to have a negligible effect on the antipolar displacements of the Fe ions lying in between SrO and LaO layers of the superlattice (i.e., within La0.5Sr0.5FeO3 unit cells). The introduction of oxygen vacancies, on the other hand, triggers a polar displacement of the Fe ions. We confirm this important result using electron energy loss spectroscopy, which shows partial oxygen vacancy ordering in the region where polar displacements are observed and an absence of vacancy ordering outside of that area.
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