Sintering and microstructure of potassium niobate ceramics with stoichiometric composition and with potassium- or niobium excess

Stoichiometric potassium niobate (KNbO3) and materials with K- and Nb excess show marked differences in sintering behaviour and microstructure. Shrinkage is shifted to lower temperatures in material with K-excess and to higher temperatures in material with Nb-excess compared to the stoichiometric KNbO3. The stoichiometric material densified to 4.36 g/cm3, whereas the densities of the off-stoichiometric materials remained lower. Abnormal grain growth leading to grains up to 500 μm in size was observed for stoichiometric KNbO3. K-excess KNbO3 shows cuboid grain shape with size between 20 and 60 μm. In the Nb-excess KNbO3 the grains remain small. Approaches to improve the densification of the KNbO3 materials are discussed by investigating processing variations specific for each composition. The objective of our work is to analyze the interrelations between stoichiometry, materials characteristics and processing stability of alkaline niobate ceramics. The results on KNbO3 mark a starting point for investigations on complex high performance systems.