Strain‐Induced Polarization Rotation in Freestanding Ferroelectric Oxide Membranes

Abstract

Freestanding ferroelectric membranes have emerged as a versatile tool for strain engineering, enabling the exploration of ferroelectric properties beyond traditional epitaxy. The resulting ferroelectric domain patterns stem from the balance at the local scale of several effects playing a key role, i.e., piezoelectricity linked to strain, and flexoelectricity arising from strain gradients. To weigh their respective contributions for a given membrane geometry, the strain profile has to be mapped with respect to the ferroelectric polarization landscape, a necessary step to allow for a controlled tailoring of the latter. In this study, the effect of bending strain on a Pb(Zr,Ti)O3 membrane is examined in a fold‐like structure, observing a polarization rotation from out‐of‐plane to in‐plane at the fold apex. Combining piezoresponse force microscopy, Raman spectroscopy, and scanning transmission electron microscopy, the ferroelectric polarization direction is mapped relative to the height profile of the membrane and the contributions of strain and strain gradients for this archetypal fold geometry are discussed. These findings offer new insights into strain‐engineered polarization configurations and emphasize strain effects at the nanoscale to tune the functional properties in freestanding membranes beyond conventional electrical methods.