Enhancement of Q_m by Co-Doping of Li and Cu to Potassium Sodium Niobate Lead-Free Ceramics

ABSTRACT Lead-free piezoelectric ceramics KNN modified by Li-substitution and CuO addition have been synthesized, and the piezoelectric and dielectric properties were measured. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was formed with Li-substitution. The co-doping of Li and Cu markedly enhanced the mechanical quality factor (Q_m) in comparison with the sole doping of Li and Cu. Anomalous anti-ferroelectric-like hysteresis curves were observed in 2 mol% CuO-doped ceramics. The anti-ferroelectric-like curves were changed to that of normal ferroelectrics following poling. A model based on the formation of the internal bias field (E_i) due to the movements of space charges was proposed to explain these phenomena. It was considered that the E_i stabilized the spontaneous polarization (P_s) and suppressed the domain wall motion to enhance the Q_m. The highest Q_m obtained in this study was 742. The [(Na_0.5K_0.5)_0.96Li_0.04] NbO₃ + 0.45 mol% CuO ceramics showed a high Q_m value of 414 with a high piezoelectric constant d₃₃ of 100 pC/N.

Digital Object Identifier 10.1109/TUFFC.2008.743

© 2008, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.

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