Microstructural evolution of crystalline-oriented (K0.5Na0.5)NbO3 piezoelectric ceramics with a sintering aid of CuO

The microstructural development of crystalline-oriented (K0.5Na0.5)NbO3 (KNN)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens containing 0.5-1.0 mol% CuO sintered at 1100 degrees C for 1 h were found to have relative densities and pseudo-cubic {100} orientation degrees of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO3 and KNbO3, after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of transmission electron microscopy observation showed that textured KNN ceramics have a unique pectinate-like domain structure with domain walls consisting of {101} planes.