Crystal Structure, Microstructure, Dielectric and Piezoelectric Properties of Lead-Free KNN Ceramics Fabricated via Combustion Method

The combustion method has been developed to prepare lead-free K0.5Na0.5NbO3: KNN ceramics. Urea and glycine were used as a fuel to reduce the reaction temperatures. The effects of fuel type, calcination and sintering conditions on phase formation, morphology evolution, density, and electrical properties were investigated. A pure orthorhombic perovskite structure was obtained from KNN powders calcined at 700 degrees C using glycine as a fuel. The average particle size increased approximately from 0.54 to 0.64 mu m as the sintering temperature increased from 650 to 700 degrees C. For the sintered ceramics, pure perovskite was found in the KNN samples sintered below 1150 degrees C. The microstructure of the KNN ceramics exhibited a square or rectangular shape and the average grain size increased with increasing sintering temperatures. The transition temperatures slightly decreased with increasing sintering temperatures. The density and dielectric constant of the ceramics tended to increase with increasing temperature up to 1050 degrees C, where it reached a value of 94.6% and 5839, respectively, and then decreased with further increase of sintering temperature. The piezoelectric d(33) value of the most-dense ceramics was 114 pC/N.