Heterogeneous diffusion and remnant hardening with excellent electromechanical compatibility in alkaline niobate composites

Both low mechanical losses and large piezoelectric coefficient (d₃₃) are essential in high-power piezoelectric applications. However, achieving both a large d₃₃ and a high mechanical quality factor (Q_m) is generally considered challenging due to the inherent trade-off between these properties. This challenge is particularly pronounced in the development of lead-free piezoelectric materials. In this work, we present a novel approach that integrates heterogeneous diffusion with remnant hardening in potassium sodium niobate (KNN)-based composites. This method results in a more than threefold increase in the Q_m, jumping from 56 to 205 while a high d₃₃ value (d₃₃ = 370 pC/N) is maintained, significantly outperforming previous reports. Structural characterization and phase-field simulations revealed that the synergistic effects of local structural heterogeneity and local stress fields achieve excellent electromechanical compatibility. This dual modulation effectively overcomes the longstanding conflict between piezoelectric properties and mechanical losses. These findings present a promising pathway to enhance the commercial viability of lead-free KNN-based piezoelectric ceramics, making a significant advancement in the development of high-performance, environmentally friendly piezoelectric materials.