Coupled phase-boundary engineering and defect control for ultrahigh electrostrain with low hysteresis in lead-free BNBT-based ceramics

The development of lead-free ferroelectric ceramics that combine high strain with low hysteresis is critical for precision actuators and displacement sensors, yet conventional (Bi0.5Na0.5)0.93Ba0.07TiO3 (BNBT) ceramics are limited by high strain hysteresis (>30%), elevated driving fields (>4 kV/mm), and poor thermal stability. Here, a Zr–Nb–vacancy co-doping strategy at Ti sites is employed to construct (Bi0.5Na0.5)0.93Ba0.07Ti1-x(Zr0.375Nb0.5□0.125)xO3 (BNBT-xZN, x = 0–0.04), enabling synergistic control of dual-phase structure and defect concentration. At x = 0.01, the ceramic exhibits coexisting rhombohedral (R3c) and tetragonal (P4bm) phases with phase fractions of 51.6% and 48.4%, respectively. This composition achieves a unipolar strain (Suni) of 0.70% and an effective piezoelectric coefficient ( ) of 1168 pm/V at 70 °C, while maintaining exceptional thermal stability. Smax remains above 0.45% across 30–150 °C and hysteresis is reduced to 8%. The enhanced electromechanical performance is attributed to a cooperative mechanism in which moderate defect concentrations reduce domain wall pinning and dual-phase interfaces lower polarization reversal energy barriers, enabling efficient domain switching. This study establishes a rational design approach for achieving ultrahigh strain and low hysteresis in lead-free ferroelectric ceramics, providing a pathway for their application in precision actuators and sensors.