Enhancement of Qm in CuO-doped compositionally optimized Li/Ta-modified (Na,K)NbO3 lead-free piezoceramics

The effects of CuO on electrical properties of compositionally optimized Li/Ta-modified (Na,K)NbO3 (LT-KNN) piezoceramics were studied to develop LT-KNN with high mechanical quality factor Qm and low dielectric loss tg δ as well as relatively high piezoelectric constant d33 for actuator applications. Both “hard” and “soft” effects were observed due to CuO addition, and the discussion related to high Li doping amount was presented to explain this phenomenon. By increasing CuO addition, the d33 gradually decreases while the Qm increases significantly. Particularly, tg δ at 1 kHz can be reduced from ∼2.7% for LT-KNN ceramics to ∼0.8% for CuO-added LT-KNN ceramics. When the CuO addition is lower than 1 mol%, both high Qm (∼323) and relatively high d33 (>180 pC/N) can be obtained, in addition to a relatively high dielectric constant ɛr ∼ 500.