Effects of K excess on the structure and properties of (K0.5Na0.5)NbO3 ceramics

There is an increasing demand to replace Pb(Zr,Ti)O₃-based piezoelectric materials with lead-free alternatives, because of the toxicity of lead oxide which is largely used during the production process. (K_0.5Na_0.5)NbO₃ is considered as one of the most promising candidates for lead free piezoelectric ceramics due to its high Curie temperature and good electrical properties. However, it is well known that dense and well-sintered K_0.5Na_0.5NbO₃ ceramics are very difficult to obtain by the ordinary sintering process owing to the high volatility of alkali elements at high temperatures. The major strategy to overcome this problem is simply adding excess alkali metals in the starting composition. In this work, the K excess lead free ceramics (K_0.5+xNa_0.5)NbO₃ (0≤x≤0.3, KNN) were prepared by a novel method mixing perovskite structure of NaNbO₃ and KNbO₃ powders. Effects of K excess and sintering temperatures on phase structure, micromorphology and electrical properties of KNN ceramics were investigated. Result showed that the KNN ceramic with x=0.2 showed optimized ferroelectric property and the single phase perovskite structure.