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

Abstract

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 complexity of nanoscale chemical and structural heterogeneity has made understanding the origins of their electromechanical properties a seemingly intractable problem. Here, we employ aberration-corrected scanning transmission electron microscopy (STEM) to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg 1/3 Nb 2/3)O 3-PbTiO 3 (PMN-PT). 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 connection between chemical heterogeneity, structural heterogeneity and local polariza

The mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO3 ceramics

“…Interestingly, the rare-earth-doped PMN-PT ceramics with enhanced piezoelectric coefficient also exhibit increased volume fraction of tetragonal phase with reduced Curie temperature and broad relaxation peak 31,36 . Tetragonal phase with low-angle domain wall was also observed in the structure evolution of PMN-PT solid solution with increasing Ti concentration based on the molecular dynamic calculation and STEM observation, being considered responsible for its high piezoelectric properties 26,37,38 .…”

“…We found the atomic columns in A and B sites by searching for the local maximums in the STEM images. Then, we calculated the polar vector for each A-site atom by measuring the vector pointing from the local centre of mass of the surrounding B sites to the actual A site 30,38,43 . We determined the position of doped elements by comparing atomic column intensities in the HAADF-STEM images, in which the contrast is proportional to the atomic numbers of elements.…”

Polar Vortexes and Charged Domain Walls in a Room Temperature Magnetoelectric Thin Film

“…In this study, we focus on the role these OPB defects play in the formation of charged domain wall (DW) and polar vortexes. We map out the pico-meter scale atomic column shifts and unit cell deformation as demonstrated previously for other ferroic materials [22][23][24][25][26], revealing the direct link between OPBs and polar topological solitons in AP thin films.…”

Growth mode and strain effect on relaxor ferroelectric domains in epitaxial 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3/SrRuO3 heterostructures

“…The exact origin of the giant piezoelectric response in PMN-PT is still under debate due to the high complexity of the microstructure and the local polar order/disorder at the MPB. [10][11][12][13][14][15] Despite the great attention received by PMN-PT in thin lm form, in particular for energy harvesting, energy storage and cooling applications, [16][17][18][19][20][21] there is still a lack of knowledge regarding epitaxial thin lms, particularly concerning correlations between the local atomic structure/strain and physical properties. 10,[22][23][24][25][26][27] Thus, understanding of the domains in relaxor ferroelectric thin lms and their evolution under external parameters such as epitaxial strain is crucial for practical applications.…”