Low-temperature sintering of K0.5Na0.5NbO3 ceramics

The objective of this work was to lower the sintering temperature of K0.5Na0.5NbO3 (KNN) without reducing its piezoelectric properties. The KNN was sintered using 0.5, 1, 2, and 4 mass% of (K, Na)-germanate. The influence of the novel sintering aid, based on alkaline germanate with a melting point near 700 degrees C, on the sintering, density, and piezoelectric properties of KNN is presented. The alkaline-germanate-modified KNN ceramics reach up to 96% of theoretical density at sintering temperatures as low as 1000 degrees C, which is approximately 100 degrees C less than the sintering temperature of pure KNN. The relative dielectric permittivity (epsilon/epsilon(0)) and losses (tan delta), measured at 10 kHz, the piezo d(33) coefficient, the electromechanical coupling and mechanical quality factors (k(p), k(t), Q(m)) of KNN modified with 1 mass% of alkaline germanate are 397, 0.02, 120 pC/N, 0.40, 0.44, and 77, respectively. These values are comparable to the best values obtained for KNN ceramics sintered above 1100 degrees C.