Optimizing Domain Structure and Switching Behavior via Tailoring Lattice Stress Distribution to Maximize Electrostrain in BF‐BT Ceramics

Lead-free BiFeO₃-BaTiO₃ (BF-BT) ceramics have great application potential in electron devices due to their good electrical property. Selecting chemical dopants meticulously has been proven to be an effective way for optimizing electrostrain performance. However, lattice stress arising from local lattice distortion after doping is always overlooked, causing a vague understanding of the relationship between lattice stress and electrostrain. To clarify this scientific puzzle, BiFeO₃-BaTiO₃-K_xNa_1- _xNbO₃ (BF-BT-K_xN_1- _xN) ceramics are designed by a strategy of co-doping with K/Na niobates, which allows for tailoring lattice stress via adjusting K⁺/Na⁺ ratio. Spherical Aberration-Corrected Scanning Transmission Electron Microscope (AC-STEM) and Geometric Phase Analysis (GPA) confirmed that altering K⁺/Na⁺ ratio can effectively regulate lattice stress distribution. The analysis, combined with Piezoelectric Force Microscopy (PFM) and Switching Spectroscopy PFM (SS-PFM), revealed that lattice stress promotes domain miniaturization, and the stress with inhomogeneous distribution significantly enhances local piezoelectric response. In addition, the uneven stress distribution can reduce the energy barrier of domain-wall motion and strengthen domain switching behavior, thus increasing macro-electrostrain, and the maximum value is achieved in BF-BT-K_0.7N_0.3N. The electrostrain is 34.2% higher than the optimized electrostrain of mono-doped sodium-niobate with equal doping amount, demonstrating the superiority of lattice stress engineering over composition design. This work establishes the association of "lattice stress-domain switching-electrostrain", providing a new paradigm and theoretical foundation for the design of high-sensitivity actuators/sensors.