Origin of large strain in La-doped 0.55BF-0.45PT ferroelectric ceramics

In this study, the components of 0.55Bi_(1-x)La_xFeO₃-0.45PbTiO₃(BF-PT45: La (x)) are designed to construct the T-R morphotropic phase boundary (MPB). A strain of 0.28% as well as a hysteresis of 26.4% at 50 kV/cm is obtained at MPB with x = 0.32. The selected area electron diffraction (SAED) results show that there is 1/2 (ooo) superlattice reflection in BF-PT45: La (0.32) ceramics. Atomic resolution aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with electron energy loss spectroscopy (EELS) confirmed that superlattice reflections are caused by a⁻b⁻b⁻ antiphase oxygen octahedral tilting rather than chemical ordering. At the same time, atomic resolution displacement vectors confirmed the coexistence of T-phase and R-phase nano-domains, and the coordination between cation displacement and oxygen octahedral tilt was evaluated using AC-STEM enhanced annular bright-field (eABF) images. Such a nano-domain structure has a low energy barrier, which is conducive to flexible dynamic polarization rotation under external stimulus. These results will have implications for understanding ferroelectric atomic-level structures and provide an effective method to attain excellent electrical properties.