K0.5Na0.5NbO3 piezoelectric ceramics and its composites fabricated from hydrothermal powders

NaNbO3 and KNbO3 powders were prepared respectively by the hydrothermal synthesis method. The obtained powders were mixed with the molar ratio of 1: 1 and dry-pressed, the (K0.5Na0.5) NbO3 (KNN) lead-free piezoelectric ceramics were obtained by sintering at 1060-1100 degrees C at normal atmosphere. The effect of sintering temperature on phase, microstructures, bulk density and electrical properties of KNN ceramics were investigated. The XRD patterns showed that the single solid solution of (Na, K) NbO3 ceramics was acquired. The SEM micrographs exhibited that increasing sintering temperature appropriately would improve grain growth and decrease porosity. K/Na, shrinkage, density, piezoelectric constant d(33) and dielectric constant increased with the increased sintering temperature. When the sintering temperature was 1100 degrees C, the d(33) reached a maximum (110.8 PC/n). Meanwhile, through freeze casting and infiltrating with a polymeric lubricant phase, a layered KNN-epoxy composite was produced using the hydrothermally synthesized NaNbO3 and KNbO3 powders as raw powders. Its microstructures and properties were analyzed.