Direct observation of weakened interface clamping effect enabled ferroelastic domain switching

Abstract

Reversible switching of non-180 degrees ferroelastic domains that largely alters the local strain distribution enables many electromechanical, electromagnetic and electroacoustic applications. However, in thin films, the ferroelastic domain walls are usually believed to be immobile because of the interface clamping and/or dislocation pinning. Here, using in situ and aberration-corrected transmission electron microscopy, we directly observe reversible switching of individual 90 degrees domains in dislocation-free PbTiO3 thin films and uncover the weakened interface clamping effect. We find the tetragonality is suppressed to similar to 1.017 while the polarization vectors rotate 45 degrees in the a-domain near the interface. These huge structural distortions at the interface is mainly responsible for the weakened clamping effect and thus the ability to switch ferroelastic domains. The switching is fully reversible (i.e., either electric field or mechanical stress can re-establish the erased domain) regardless of polarization orientation of the c-domain matrix. Phase-field modeling also shows excellent agreement with experimental observations. Our study reveals the mechanism of controllable and reversible ferroelastic domain switching, enabling the design of new actuators, sensors, and electromagnetic devices. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.