Mechanochemical synthesis and mechanochemical activation-assisted synthesis of alkaline niobate-based lead-free piezoceramic powders

Abstract

Instead of conventional solid-state reactions and wet-chemistry-based processes for the synthesis of alkaline niobate-based lead-free piezoceramic powders, the research progress of the mechanochemical synthesis and the mechanochemical activation-assisted synthesis processes have been attractive owing to their unique advantages such as no volatilization of alkaline species, chemical homogeneity, and refined crystals of synthesized powders. The formation of intermediate amorphous carbonato complex during high-energy ball milling was found to be essential for the formation of NaNbO 3 (NN), KNbO 3 (KN), and (K,Na)NbO 3 (KNN) during the further milling or subsequent calcination. The synthesis behavior was dependent on the relative magnitude of the activation energy barrier and the cumulative kinetic energy. Since LiNbO 3 and NN powders were relatively easily synthesized by planetary milling for a short time, their activation energies were thought to be low. Only a small fraction of KN and no KNN powders were synthesized by planetary milling indicating their higher activation energy. Even KNN has a high activation energy, mechanochemical synthesis of KNN powders could be achieved by applying shaker milling which was thought to provide higher cumulative kinetic energy. From the viewpoint of practical applications, mechanochemical activation-assisted process will be recommended for the synthesis of KNN rather than mechanochemical synthesis because the latter produced severely agglomerated powders which resulted in poor sinterability.