In situ TEM dark-field observation on ferroelectric/ferroelastic domain evolution in ferroelectrics sub-micrometer pillar under stress

The evolution of ferroelectric/ferroelastic domains in ferroelectric materials (FMs) under stress fields is a significant yet complex process. This process involves the interaction of hierarchical domain structures across scales, as well as the coupling of elastic and electrical potentials. To understand the critical local microstructure evolution, here we used in situ transmission electron microscopy (TEM) to directly observe the hierarchical domain evolution induced by stress in BaTiO₃ and Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) sub-micrometer pillars. The results indicate that domain evolution is sensitive to the loading methods, including loading/unloading speed, stress maintenance duration, and stress amplitude. Assisted by phase-field simulations, we have proved that mobile point defect pinning effect also influence the domain evolution greatly. Based on above understanding, we successfully achieved a large recoverable deformation in PMN-PT pillar with 10% strain. Our findings provide a novel avenue to develop super-flexibility in FMs.