Ion-channel-mediated gradient acceptor distribution for hard lead-free piezoceramics

Simultaneously optimizing the piezoelectric coefficient (<i>d</i>₃₃) and mechanical quality factor (<i>Q</i>_m) presents a fundamental challenge in developing high-performance piezoceramics for high-power applications. While conventional hardening approaches, like acceptor doping, can improve <i>Q</i>_m, they typically sacrifice <i>d</i>_33-an inherent trade-off that limits material performance. In this study, we propose an innovative strategy utilizing ion-conductive K₂Ti₆O₁₃ (KT) rod-shaped secondary phase as functional ionic channels to create spatially graded acceptor distribution in potassium sodium niobate (KNN)-based lead-free ceramics. This strategy achieves unprecedented property synergy, yielding simultaneous enhancements of 36% in <i>d</i>₃₃ and 64% in <i>Q</i>_m. Through multiscale characterization combining aberration transmission electron microscopy and phase-field simulations, we reveal that the KT-mediated gradient distribution of Cu ions induces localized domain activation in certain regions while enhancing pinning effects in others. This unique microstructure establishes a dynamic balance between domain wall mobility and stabilization, ultimately optimizing the overall piezoelectric response. This ion-channel-assisted heterogeneous doping strategy establishes a new design paradigm for overcoming the traditional <i>d</i>₃₃-<i>Q</i>_m compromise, opening avenues for next-generation lead-free piezoelectrics in high-power electromechanical systems.