Realizing Ultrahigh Polarization and Excellent Thermal Stability in Piezoceramics via Defect‐Stress Engineering

Large polarization is critical for improving the piezoelectric and actuation performance of ferroelectric materials. As a promising lead‐free candidate, BiFeO 3 ‐BaTiO 3 inherits the excellent polarization capability of BiFeO 3 . However, the actual polarization achieved in its ceramics remains far below the theoretical predictions. In this work, we propose a novel defect‐stress engineering strategy to enhance the polarization substantially. By intentionally introducing A‐site vacancies into 0.70BiFeO 3 ‐0.30BaTiO 3 ceramics, combined with quenching treatment, localized stress‐concentration regions are formed within the ceramic matrix. This strategy successfully achieves a remarkable increase in polarization displacement and promotes the formation of polar nanoregions. Under an electric field of 60 kV/cm, the optimized ceramics exhibit a high remanent polarization of 46.40 µC/cm 2 , which is significantly superior to that of most reported lead‐free counterparts. Moreover, the unipolar strain shows only a 13% variation from room temperature to 180°C, demonstrating excellent thermal stability. This work confirms that defect‐stress engineering is an effective approach to enhance polarization in bulk lead‐free ferroelectrics and provides a new framework for developing lead‐free ferroelectric materials with both high polarization and superior temperature stability.