Effects of AETiO3 additions on phase structure, microstructure and electrical properties of (K0.5Na0.5)NbO3 ceramics

Lead-free piezoelectric ceramics with the composition Of (K0.5Na0.5)NbO3 (KNN) and 0.995(K0.5Na0.5)NbO3-0.005AETiO(3) (AE=Mg, Ca, Sr, Ba) were successfully prepared by conventional ceramic processing. Single perovskite phase with orthorhombic syngony can be obtained in pure KNN, KNN-CT and KNN-ST ceramics. The trace amounts of secondary phase(s) can be detected in KNN-MT and KNN-BT ceramics. Ceramics of KNN-CT and KNN-ST have higher cell parameters and higher densities than those of pure KNN ceramics. Good electrical properties (d(33) = 122 pC/N, K-p = 0.38, epsilon(r) = 421, tan delta = 0.033 and T-C = 406 degrees C) can be obtained in pure KNN ceramics. The KNN-CT ceramics have optimized electrical properties, which are d(33) = 116 pC/N, K-p = 0.39, epsilon(r) = 411, tan delta = 0.024 and T-C = 397 degrees C. Besides, the P-r is 18.8 mu C/cm(2) and the E, is 9.65 kV/cm for pure KNN ceramics. By adding AET to KNN, the P-r values decrease with increasing the AE ions radii. The air-sintered pure KNN and KNN-CT ceramics are promising lead-free piezoelectric materials for transducer applications. (c) 2006 Elsevier B.V. All rights reserved.