Evolution of Crystallographic Grain Orientation of (K_0.5Na_0.5)NbO₃ Piezoelectric Ceramics

The microstructural development of crystalline-oriented (K0.5Na0.5)NbO3 (described as KNN hereafter)-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 with 0.5-1.0 mol% CuO sintered at 1100ºC for 1 h have both a relative density and a pseudo-cubic {100} orientation degree 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 TEM observation showed that textured KNN ceramics have a unique pectinate-like domain structure, in which the domain walls consist of {101} planes.