Shear-mode piezoelectric properties of modified-(K,Na)NbO₃ ceramics for "hard" lead-free materials

(K_0.45Na_0.55)NbO₃-0.5 mol% K ₄CuNb₈O₂₃ [KNN-KCN] solid solution was synthesized and its shear mode dielectric and piezoelectric properties were characterized as a function of temperature. The doped KNN material was found to possess comparable electric resistivity, piezoelectric, and electromechanical properties with pure KNN, but with a much higher mechanical Q_m value, being on the order of 1500. The dielectric permittivity K₁₁ ^T and piezoelectric coefficients d₁₅ for KNN-KCN were found to increase with the increasing temperature, while the electromechanical coupling factors k₁₅ maintain a similar value till the phase transition temperature (T_o-t∼200°C), above which, the properties drop significantly due to depolarization. The good temperature-dependent properties, together with its high mechanical Q _m, demonstrate a practical potential of KNN-KCN materials for high power shear-mode applications.