Large Strain in CuO‐added (Na_0.2K_0.8)NbO₃ Ceramic for Use in Piezoelectric Multilayer Actuators

Abstract

In this study, 1.0 mol% CuO-added (Na x K 1 -x )NbO 3 (CN x K 1 -xN) ceramics with 0.0 ≤ x ≤ 0.5 were sintered at a relatively low temperature of 960°C. A large Q m value (≥1750) was obtained for the specimens with x ≤ 0.2 owing to the hardening effect of Cu 2+ ions, indicating that a large number of Cu 2+ ions had replaced Nb 5+ 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 (P d ) formed between Cu 2+ ions and O 2 -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 P d . For the CN 0.2 K 0.8 N 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 10 4 cycles when a high electric field of 8.0 kV/mm was continuously applied to the specimens during each cycles. Therefore, CN 0.2 K 0.8 N is a useful lead-free piezoelectric ceramic for multilayer actuators.

Thermally stable large strain in low‐loss (Na0.2K0.8)NbO3‐BaZrO3for multilayer actuators

“…Figure 9 displays unipolar S-E curves of this specimen obtained at different temperatures. 22 It is worth noting that a normal P-E loop was observed in the sample with x = 0.04 at 175°C, but this sample maintained large values of the strain (≥0.17%) up to 200°C. Slightly increased strains, close to 0.2%, were observed at temperatures in the range of 25-75°C.…”

“…14 Therefore, for the practical application to piezoactuators, the size of the S-E curve should be reduced and the thermal stability of the strain must be improved. [20][21][22][23] These leadfree ceramics showed large strains as they do not have S r . [15][16][17][18][19] The sprout-shaped S-E curves of these specimens were attributed to the presence of the defect polarization (P D ) between Mn 3+ ions and oxygen vacancies.…”

“…The Mn-doped (Ba 0.95 Sr 0.05 )TiO 3 , (K, Li)(Nb, Ta) O 3 , KNbO 3 , and BaTiO 3 lead-free ceramics exhibited large electric-field-induced strains (0.12%-0.15%), owing to their sprout-shaped S-E curves without S r . [20][21][22] However, these ceramics showed large S-E (or P-E) curves, revealing their large dielectric losses. [15][16][17][18][19] Sprout-shaped S-E curves without S r were also observed for CuO-doped KNbO 3 , (Na 0.5 K 0.5 )NbO 3 , and (Na 0.2 K 0.8 )NbO 3 ceramics, owing to the development of P D between Cu 2+ ions and oxygen vacancies.…”

“…[15][16][17][18][19] The sprout-shaped S-E curves of these specimens were attributed to the presence of the defect polarization (P D ) between Mn 3+ ions and oxygen vacancies. [20][21][22] Therefore, it is required to reduce the sizes of the S-E curves of these ceramics to reduce the dielectric losses for their practical application to piezoelectric actuators. [20][21][22][23] These leadfree ceramics showed large strains as they do not have S r .…”

“…24 However, the thermal stability of the CuOdoped KNbO 3 ceramic was low, leading to a small effective strain at 75°C, 24 which hinders the application of CuO-doped KNbO 3 -BaZrO 3 ceramics in piezo actuators. 22 Therefore, the CNKN ceramic could be used for the development of lead-free piezo actuators if the dielectric loss (or size of its S-E curve) was reduced. This ceramic also exhibited good fatigue properties.…”