Competing effects of temperature and mechanical stress on polar vortex transition in oxide superlattices

The interplay of different forms of energies in oxide superlattices, such as elastic, electrostatic, and gradient energies, can result in a stable long-range ordered polar vortex structure at room temperature. However, the role between these energies in determining the vortex structure still remains largely elusive due to the intricate interplay. By using a comprehensive in situ TEM apparatus and a prototype system, PbTiO3/SrTiO3 superlattice, we demonstrate that the vortex structure undergoes a first-order transition at the temperature around 653 K, while the application of in-plane mechanical stress at such a high temperature results in the reemergence of vortex structure. Cryogenic cooling to 94 K raises the stability of vortices, which would be destabilized by loading of out-of-plane mechanical stress. The results can be reproduced and well interpreted by phase-field simulations. These findings not only reveal the competing role of the temperature and mechanical stress at atomic scale but also demonstrate a feasible way to operate the vortex-based nanodevices working in harsh environments.