Large Strain in CuO-added (Na0.2K0.8)NbO3 Ceramic for Use in Piezoelectric Multilayer Actuators

In this study, 1.0 mol% CuO‐added (NaxK1−x)NbO3 (CNxK1−xN) ceramics with 0.0 ≤ x ≤ 0.5 were sintered at a relatively low temperature of 960°C. A large Qm value (≥1750) was obtained for the specimens with x ≤ 0.2 owing to the hardening effect of Cu2+ ions, indicating that a large number of Cu2+ ions had replaced Nb5+ ions in these ceramics. The double polarization versus electric field (P–E) hysteresis loop was observed for the specimens with x ≤ 0.2, and was explained by the defect polarization (Pd) formed between Cu2+ ions and O2− vacancies. These specimens also exhibited a sprout‐shaped strain versus electric field (S–E) curves with a large strain of 0.14%–0.15% at 8.0 kV/mm because of the internal bias field produced by Pd. For the CN0.2K0.8N ceramic, a double P–E hysteresis loop was maintained at 125°C without remnant polarization. Moreover, this ceramic showed a large strain of 0.175% after 104 cycles when a high electric field of 8.0 kV/mm was continuously applied to the specimens during each cycles. Therefore, CN0.2K0.8N is a useful lead‐free piezoelectric ceramic for multilayer actuators.