Hardening of K_0.5Na_0.5NbO₃ lead-free ceramics by adding Ag₂O and CuO and crystal-orientation behavior of their powders under a high magnetic field

The hardening of K_0.5Na_0.5NbO₃ (KNN) ceramics with the addition of Ag₂O and CuO and the crystal-orientation behavior of KNN and CuO-added KNN powders under a high magnetic field were investigated. Ag₂O reduced the degree of compositional deviation of KNN ceramics and increased their density. Additionally, the piezoelectric characteristics were improved by the addition of Ag₂O. CuO functioned as a sintering aid for KNN, and the CuO-added KNN ceramics increased the grain size and mechanical quality factor by up to approximately 1200. The simultaneous addition of Ag₂O (0.01 mol) and CuO (0.01 mol) to KNN resulted in hardening with a mechanical quality factor of 1400 owing to the synergistic contributions of each additive. Under a high magnetic field of 5 T, the KNN powder and CuO (0.01 mol)-added KNN powder exhibited b- and c-axes orientation parallel to the magnetic field, which is expected to enhance the piezoelectric properties through crystal orientation.