Fabrication of (K,Na)NbO3-based composite lead-free piezoelectric ceramics and their high-power properties

Mn-added (K,Na)NbO3-based composite lead-free piezoelectric ceramic containing KTiNbO5 phase was fabricated for potential application to high-power fields. The resulting (K,Na)NbO3-based composite ceramic with 2 mol % MnO2 exhibited piezoelectric properties (mechanical quality factor Qm = 650, piezoelectric constant d33 = 140 pC/N, electromechanical coupling coefficient kp = 0.42, dielectric constant ε33T/ε0 = 750, dielectric loss tan δ = 0.5 %), and adequate heat resistance (Curie temperature Tc = 320 °C). It exhibited an internal electric field, as indicated by a shift of the polarization–electric field hysteresis loop in the direction of the electric field. High-power characteristics of bolt-clamped Langevin transducers prepared using the (K,Na)NbO3-based composite ceramic was superior to those of a Pb(Zr,Ti)O3 ceramic at a vibration velocity under high input voltage. The (K,Na)NbO3-based composite ceramic has good high-power properties and adequate heat resistance, dense microstructure, and process stability, and is considered to be a promising candidates as lead-free piezoelectric ceramics for high-power devices, such as ultrasonic motors, transformers, and transducers.