Heterogeneous-stacking strategy for simultaneously achieving high d33 and Qm in (K,Na)NbO3-based piezoceramics

The (K,Na)NbO3 (KNN) system is regarded as a highly promising lead-free piezoelectric material, characterized by the high piezoelectric coefficient (d33) and Curie temperature (TC). However, for high-power applications, a high mechanical quality factor (Qm) is equally crucial alongside a large d33. Coordinating these two properties is challenging due to their divergent dependencies on extrinsic contributions. To address this, we designed and fabricated a sandwich-structured KNN-based piezoceramic using a heterogeneous-stacking strategy. This structure features a high-Qm (K0.46Na0.52Li0.02) (Nb0.94Sb0.04Sn0.005Fe0.005Mn0.005Cu0.005)O3 (hard-KNN) middle layer (Qm = 948, d33 = 132 pC/N), with textured 0.97K0.5Na0.5Sb0.03Nb0.97O3-0.03Bi0.5Na0.5ZrO3- 0.5wt %BiFeO3-x wt %Cu (T-KNN- xCu) serving as the outer layers to provide high d33. Through the synergistic effect between the high-Qm hard-KNN and high-d33 T-KNN-xCu layers, the sandwich-structured ceramic achieved an excellent combination of properties: a d33 of 300 pC/N, a Qm of 158, and a kp of 49.1%. In conclusion, this work not only provides new approach for achieving high d33 and Qm performances, but also develops the KNN-based lead-free piezoceramics with application potential in replacing the PZT-4 piezoelectric ceramics.