Grain Engineering Modification of Temperature-Insensitive High Piezoelectricity in Bi0.5Na0.5TiO3-Based Ceramics at Morphotropic Phase Boundary.

The practical application of lead-free Bi0.5Na0.5TiO3 (BNT)-based piezoelectric ceramics is limited by the persistent trade-off between piezoelectric coefficient (d33) and thermal stability, which conventional compositional strategies fail to resolve. Here, we propose a grain engineering approach to decouple this property conflict by directly designing the microstructure of BNT-based ceramics at the morphotropic phase boundary. Rather than relying on complex chemical modifications, grain morphology is modulated to regulate the ferroelectric-to-relaxor transition. The optimized ceramic exhibits a d33 of ∼180 pC/N, a coercive field Ec of 23.6 kV/cm, a remnant polarization Pr of 34.5 μC/cm2, and a depolarization temperature (Td) of 125 °C, while maintaining less than 2% variation in d33 from 30 to 110 °C. This temperature-insensitive d33 originates from grain-engineered multiphase coexistence, which maintains a high piezoelectric response while stabilizing the field-induced long-range ferroelectric order against thermal depolarization. These findings highlight grain engineering as a robust microstructural strategy for developing high-performance, temperature-stable lead-free piezoceramics, paving the way for their use in high-precision devices under fluctuating thermal environments.