Sintering effect on microstructure and properties of (K,Na) NbO₃ ceramics

(K,Na)NbO₃ (KNN) lead-free ceramics were fabricated using conventional solid-state reaction method. The domain configurations were studied with transmission electron microscopy and found to be closely related to the sintering temperature and cooling rate. High density ceramics with uniform compositions were obtained when sintered at 1200°C with a slow cooling rate, resulting in the improved piezoelectric properties, with d₃₃ on the order of 150-160 pC/N, which is comparable to the hot pressed KNN ceramics. The microstructures of the ceramics synthesized at various conditions were explained in terms of the solid-solution characteristics of KNN system, based on the high temperature phase diagram. The relationship of processing parameter- microstructure-property established herein will lead to further improvements in the piezoelectric properties of KNN lead-free materials.