Strain-Inhibited Electromigration of Oxygen Vacancies in LaCoO₃

The oxygen vacancy profile in LaCoO₃ exhibits rich phases with distinct structures, symmetries, and magnetic properties. Exploration of the lattice degree of freedom of LaCoO₃ in the transition between these different structural phases may provide a route to enable new functionality in oxide materials with potential applications. To date, the oxygen vacancy profile transition in LaCoO₃ has mainly been induced by transition-metal doping or thermal treatment. Epitaxial strain was proposed to compete with the lattice degree of freedom but has not yet been rationalized. Here, the experimental findings of strain-inhibited structural transition from perovskite to brownmillerite during the electromigration of oxygen vacancies in epitaxial LaCoO₃ thin films are demonstrated. The results indicate that the oxygen vacancy ordering phase induced by the electric field is suppressed locally by both epitaxial strain field and external loads shown by in situ aberration-corrected (scanning)/ transmission electron microscopy. The demonstrated complex interplay between the electric and strain fields in the structural transitions of LaCoO₃ opens up prospects for manipulating new physical properties by external excitations and/or strain engineering of a substrate.