Mesoscale inhomogeneity across morphotropic phase boundary in relaxor ferroelectrics

Relaxor ferroelectrics have drawn much attention due to the intriguing physics underneath their giant piezoelectric properties. The extraordinary electromechanical responses are facilitated by metastable polarization states around the morphotropic phase boundary between rhombohedral and tetragonal symmetries. The highly frustrated lattice distortions give rise to a hierarchical evolution of polar order and make mesoscale mechanism especially important for relaxor ferroelectrics. In this talk, I will provide a comprehensive picture of the spatial ordering heterogeneities in the canonical relaxor ferroelectric 0.68PbMg_1/3Nb_2/3O₃-0.32PbTiO₃ (PMN-PT) film epitaxially synthesized on SmScO₃ substrate. Combining X-ray nanodiffraction and X-ray photon correlation spectroscopy (XPCS), we resolved the detailed lattice distortions of both strain and lattice tilt in the nanoscale. Our result showed a continuous distribution of entangled polarization without hard domain walls. The in-operando evolution of the strain and lattice under the applied electric field further revealed an inhomogeneous evolution of polarization rotation enhanced by local structural variation across the morphotropic phase boundary. I will also discuss how nanoprobe and XPCS could work cooperatively in probing the polar order distribution and providing a more comprehensive picture of domain response under applied electric fields.