Simultaneous Enhancement of Piezoelectricity and Mechanical Quality Factor in Hard-Type KNN-Based Lead-Free Ceramics via Hierarchical Domain Architecture

Abstract

High mechanical quality factor (Qm) and low mechanical loss are crucial for the performance of piezoelectric materials in high-power applications. Although potassium sodium niobate (KNN) based ceramics are promising candidates for lead-free piezoelectric materials due to their favorable piezoelectric performance and environmental benefits, they traditionally face a trade-off between high piezoelectric coefficient (d33) and Qm. To address this long-standing issue, a multivalent acceptor codoping strategy is presented that innovatively induces hierarchical domain structure in hard-type KNN-based piezoceramics, significantly increasing domain wall density and pinning strength while maintaining well-ordered ferroelectric domain structure, thereby achieving a simultaneous enhancement of Qm, d33 and thermal stability. The optimized composition possesses a high Qm up to 948 with a d33 of 132 pC/N, representing improvements of 80% and 25% compared to Cu-doped samples, and maintaining outstanding performance with Qm > 800, d33 > 130 pC/N across a broad temperature range of 25–175 °C. Furthermore, our sample retained high Qm performance under high-power conditions, outperforming several commercial lead-based ceramics. These results provide new insights into the defect-domain interaction of hard-type KNN-based ceramics and demonstrate their potential for lead-free high-power piezoelectric applications.