Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics

Relaxor ferroelectric systems exhibit exceptional electromechanical coupling that arises from a variety of nanoscale chemical ordering. Here, scanning transmission electron microscopy is used to quantify this structural complexity directly. Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling, are some of the most important functional materials, with applications ranging from ultrasound imaging to actuators. Since their discovery, their complex nanoscale chemical and structural heterogeneity has made the origins of their electromechanical properties extremely difficult to understand. Here, we employ aberration-corrected scanning transmission electron microscopy to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg1/3Nb2/3)O-3-PbTiO3. We identify three main contributions that each depend on Ti content: chemical order, oxygen octahedral tilt and oxygen octahedral distortion. These heterogeneities are found to be spatially correlated with low-angle polar domain walls, indicating their role in disrupting long-range polarization and leading to nanoscale domain formation and the relaxor response. We further locate nanoscale regions of monoclinic-like distortion that correlate directly with Ti content and electromechanical performance. Through this approach, the connections between chemical heterogeneity, structural heterogeneity and local polarization are revealed, validating models that are needed to develop the next generation of relaxor ferroelectrics.

Automated summary

Scanning transmission electron microscopy is used to quantify the structural complexity of relaxor ferroelectric systems, revealing the spatial correlation between nanoscale heterogeneities and local polarization. Three main contributions related to Ti content include chemical order, oxygen octahedral tilt, and oxygen octahedral distortion, which disrupt long-range polarization and lead to nanoscale domain formation and the relaxor response. Nanoscale regions of monoclinic-like distortion directly correlate with Ti content and electromechanical performance, validating models needed for the development of the next generation of relaxor ferroelectrics.