Normal Sintering of (K,Na)NbO3-Based Ceramics: Influence of Sintering Temperature on Densification, Microstructure, and Electrical Properties

Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO₃–NaNbO₃, KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d ₃₃ value of 206 pC/N was obtained for the Li- and Ta-codoped KNN ceramics prepared at 1090°C.