The fabrication and transfer of freestanding single-crystal ferroelectric membranes deserve intensive investigations as to their potential applications in flexible wearable devices, such as flexible data storage devices and varied sensors in E-skin configurations. In this report, we have shown a comprehensive study approach to the acquisition of a large-area freestanding single-crystal ferroelectric BaTiO₃ by the Sr₃Al₂O₆ scarification layer method. By controlling the thickness of the BaTiO₃ and Sr₃Al₂O₆, the exposed area of the Sr₃Al₂O₆ interlayer, and the utilization of an additional electrode La_2/3Sr_1/3MnO₃ layer, the crack density on the freestanding BaTiO₃ can be dramatically decreased from 24.53% to almost none; then, a more than 700 × 530 μm² area high-quality freestanding BaTiO₃ membrane can be achieved. Our results offer a clear and repeatable technology routine for the acquisition of a flexible large-area ferroelectric membrane, which should be instructive to other transition metal oxides as well. Our study can confidently boost flexible device fabrication based on single-crystal transition metal oxides.

In an electrocatalytic process, the cognition of the active phase in a catalyst has been regarded as one of the most vital issues, which not only boosts the fundamental understanding of the reaction procedure but also guides the engineering and design for further promising catalysts. Here, based on the oxygen evolution reaction (OER), the stepwise evolution of the dominant active phase is demonstrated in the LaNiO₃ (LNO) catalyst once the single‐crystal thin film is decorated by LNO nanoparticles. It is found that the OER performance can be dramatically improved by this decoration, and the catalytic current density at 1.65 V can be enhanced by ≈1000% via ≈10⁹ cm⁻² nanoparticle adhesion after extracting the contribution of surface enlargement. Most importantly, a transition of the active phase from LNO to NiOOH via surface reconstruction with the density of LNO nanoparticles is demonstrated. Several mechanisms in terms of this active phase transition are discussed involving lattice orientation‐induced change of the surface energy profile, the lattice oxygen participation, and the A/B‐site ions leaching during OER cycles. This study suggests that the active phases in transition metal‐based OER catalysts can transform with morphology, which should be corresponding to distinct engineering strategies.