Tuning the Covalency of A-O Bonds to Improve the Performance of KNN-Based Ceramics with Multiphase Coexistence.

Although a room-temperature multiphase coexistence (MPC) strategy improves the piezoelectric coefficient (d33) of potassium sodium niobate ((K,Na)NbO3, KNN) ceramics, it still suffers from the dependencies on composition and temperature, making it remain challenging to further improve d33 and temperature stability of strain for an already-built MPC. Here, we proposed a new route to resolve this issue, that is, tuning the covalency of A-O bonds in an already-built MPC. We chose 0.96(Na0.60K0.40)(Nb0.955Sb0.045)O3-0.04(Bi0.5Na0.5)ZrO3 ceramics as an already-built MPC and replaced (Bi0.5Na0.5)2+ with Ba2+ to tune the covalency of A-O bonds. Thus, we synthesized 0.96(Na0.60K0.40)(Nb0.955Sb0.045)O3-0.04(Bi0.5Na0.5)1-xBaxZrO3 ceramics. We not only improved d33 values from 450 pC/N (at x = 0) to 500-505 pC/N (at x = 0.05-0.10) but also obtained the enhanced temperature stability for strain at x = 0.10, outperforming that of samples with x = 0 and other KNN-based ceramics. The increased d33 is attributed to the well-preserved MPC and the repaired long-range ordering, and the improved temperature stability of strain is due to shifting the MPC to a slightly higher temperature than room temperature. Therefore, the new route is useful to further improve the performance of an already-built MPC, benefiting to the future design of MPC and the practical application of KNN-based ceramics.