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Sinterability and Piezoelectric Properties of (K,Na)NbO3 Ceramics with Novel Sintering Aid

Dense (K,Na)NbO3 (KNN)-based ceramics were developed by optimizing the sintering conditions with newly developed K4CuNb8O23 (KCN) as a sintering aid. The sinterability and electrical properties of KNN ceramics were investigated as a function of KCN concentration. The density of KNN ceramics increased monotonically with increasing the KCN contents, and reached the highest value of 4.40 g/cm3 with the addition of 0.5 mol% KCN. This is due to the formation of liquid phase, which significantly promotes the densification of KNN ceramics. The Curie temperature (Tc) of pure KNN ceramics was 420°C and decreased with increasing the KCN content. With the addition of 0.5 mol% KCN, planar mode electromechanical coupling factor (kp) and mechanical quality factor (Qm) of KNN ceramics also reached the highest values of 0.39 and 1200, respectively. The KNN ceramics prepared with 0.5 mol% KCN exhibited a large field-induced strain of 0.09% at 40 kV/cm and the piezoelectric constant d33 of 180 pm/V.