Professors Sun Jun, Ding Xiangdong, and Wu Haijun from the School of Materials Science and Engineering together with a research team from Sichuan University have made progress in the regulation of the domain structure of lead-free sodium bismuth titanate-based relaxor ferroelectric ceramics.

The team used fine composition control to discover and confirm the nano-scale vesicular ferroelectric domain structure with multipolar topological configuration in bulk ferroelectric ceramics for the first time.

They used spherical aberration-corrected scanning transmission electron microscopy and piezoelectric force microscopy to perform real-space imaging of the topological morphology in the bubble ferroelectric domains, and used phase-field simulations to reveal that the observed phenomenon originated from the interaction of bulk energy, elastic energy, and electrostatic energy in the strong and weak spontaneously polarized ferroelectric phases.

This work provided a new idea for studying the topological domain structure in bulk ferroelectric materials.

The film material can effectively control the polarization field and the depolarization field, so by changing the epitaxial stress between the ferroelectric layer and the paraelectric layer, the topological domain structure can be controlled in the multilayer film.

However, this kind of effective epitaxial stress is not suitable for bulk materials, which limits the application of these topological structures with rich physical properties in bulk ferroelectric materials.

The total free energy of bulk ferroelectric materials is mainly modulated by the bulk energy, elastic energy and electrostatic energy of the coexisting phase, which also determines the configuration of the ferroelectric domains finally observed.

Relaxor ferroelectric ceramics, as a class of functional materials with excellent electromechanical coupling response, have attracted more and more researchers in recent years to explore their multi-phase coexistence microstructure.

This paper is the first to discover and confirm the existence of bubble ferroelectric domains in bulk ferroelectric ceramics, and points out the possibility of polar skyrmions in this type of material. 

Illustrations: A. The strategy of inducing bubble ferroelectric domains by chemical modification in bismuth sodium titanate-based relaxor ferroelectric ceramics. B. Real-space imaging of potential polar skyrmions with STEM corrected for spherical aberration. C. The results of phase-field simulation reveal a variety of polar structures in bulk ferroelectric materials. D. Bubble domains evolve into "doughnut"-like ferroelectric domain structures under the action of an external electric field, which may have potential application value in high-density storage.

The results were published on Nature Communications under the title "Nanoscale bubble domains with polar topologies in bulk ferroelectrics".

XJTU is the first corresponding unit of the paper. Professor Wu Haijun from the the School of Materials Science and Engineering, Professor Wu Jiagang from Sichuan University, and Professor Stephen J. Pennycook from the National University of Singapore are the co-corresponding authors. Associate Professor Zong Hongxiang from the School of Materials Science and Engineering is the co-first author of the paper.

The research was supported by the XJTU Young Talents Program and the school's Instrumental Analysis Center for electron microscope qualitative and quantitative structure characterization and analysis.

Link to the article: https://www.nature.com/articles/s41467-021-23863-w