Microstructural Evolution of Crystalline‐Oriented (K _0.5 Na _0.5 )NbO ₃ Piezoelectric Ceramics with a Sintering Aid of CuO

The microstructural development of crystalline‐oriented (K 0.5 Na 0.5 )NbO 3 (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°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 NaNbO 3 and KNbO 3 , 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.