Ultrahigh strain in BF–BT ceramics via synergistic optimization of defect dipoles and electric field gradient

The development of high-performance lead-free piezoelectric ceramics is critical for advancing precision actuation equipment while mitigating the environmental toxicity associated with lead-based materials. Herein, a synergistic strategy combining defect dipoles with electric field gradient was proposed to improve the strain characteristics of BiFeO₃–BaTiO₃ (BF–BT) ceramics. Through introducing the component KTaO₃ (KT), it is found that defect dipoles [(Fe' Ti–V •• O)^• and (Mn'' Ti–V •• O)^×] and relaxor characteristics are mediated, and that a unique domain structure is also created in BF–BT–0.015KT ceramic, in which island domains are surrounded by stripe domains, showing fast response to external field. Moreover, reducing the sample thickness enables a significant increase in the electric field gradient at electrode edges, thereby enhancing the macroscopic strain induced by bending deformation. Finite element analysis results indicate that the electric field gradient at the electrode edge in thin samples is greater than that in thick samples by approximately one order of magnitude. Accordingly, an ultrahigh strain of 1.13%, a high Curie temperature of 374 ℃, excellent cyclic stability (4×10⁵ cycles, degrades by 7.9%), and good thermostability (25–150 ℃, varies by 8.3%) are simultaneously achieved in the BF–BT–0.015KT ceramic with a thickness of 0.15 mm and an electrode radius of 4 mm. The findings provide a novel perspective for understanding the bending deformation and identify a promising material for developing high-performance lead-free piezoelectric bending actuators.