1-x)K 0.5 Na 0.5 Nb 1-y Sb y O 3 -zSrZrO 3 -xBi 0.5 Na 0.5 HfO 3 (KNNS-SZ-BNH) lead-free ceramics were developed by the conventional solid-state reaction method. Effects of the additives (Bi 0.5 Na 0.5 HfO 3 , SrZrO 3 and Sb 5+ ) on their phase structure, microstructure, and electrical properties were investigated. The rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary can be established in the ceramics with 0.03≤x≤0.05, 0.04≤y≤0.06, and 0.01≤z≤0.025, and then their piezoelectric properties were improved. The ceramics with x=0.03, y=0.04 and z=0.01 possess the optimum piezoelectric properties (d 33 =470±5 pC/N, k p =0.51±0.02, andT C =244 o C). We believe that R-O-T multiphase coexistence is mainly responsible for the enhancement of piezoelectric properties.

It is a tough issue to develop dense and water resistant KNbO ceramics due to high evaporation and hygroscopicity of KO. Here, KNbO:xZnO composite ceramics were used to successfully solve this problem, where ZnO particles were randomly distributed into a KNbO matrix. The addition of ZnO hardly affects the phase structure of KNbO, and moreover, the enhancement of electrical properties, thermal stability, and aging characteristics was observed in KNbO:xZnO composite ceramics. The composites possessed the maximum d of 120 ± 5 pC/N, which is superior to that of pure KNbO (d = 80 pC/N). More importantly, a strong water resistance and an aging-free characteristic were observed in KNbO:0.4ZnO. This is the first time for KNbO ceramics to simultaneously improve electrical properties and resolve the water-absorbing properties. We believe that these composite ceramics are promising for practical applications.