Influence of the A/b stoichiometry on defect structure, sintering, and microstructure in undoped and Cu-doped KNN

Abstract

Development of ceramics based on the alkaline niobate (KNN) system is one of the major lines of current research pointing to substitution of the lead containing ferroelectrics by lead-free materials. Sodium potassium niobate (K0.5Na0.5)NbO3 is a prototype material of lead-free alkaline-transition metal ferroelectrics with perovskite structure. Processing procedures for KNN-based ceramics are however challenging due to the hygroscopic behavior of sodium- and potassium carbonates and the evaporation of alkalines at the elevated processing temperatures, which make it difficult to control the stoichiometry of the ceramics. Alkaline (A-site) or niobium (B-site) excess results in pronounced qualitative differences of the microstructure in KNN ceramics.