Microstructure and Piezoelectric Properties of (K_0.5Na_0.5)NbO₃–BaTiO₃ Lead‐Free Piezoelectric Ceramics Modified by B₂O₃–CuO

A combined sintering aid mixture of B₂O₃ and CuO for lead‐free piezoelectric ceramics having the composition 0.95K_0.5Na_0.5NbO₃–0.05BaTiO₃ (KNN‐BT) is introduced. The effects of the sintering aid mixture of 0.6B₂O₃–0.4CuO on the sintering behavior, microstructure, and electrical properties of KNN‐BT are investigated. Adding 2 wt% of the sintering aid mixture can effectively broaden the narrow sintering temperature range having a size of 20°C to above 50°C and increase the grain size of samples as well as maintain the high density of samples sintered at a low temperature. The increase in grain size contributes to an improvement in electrical properties. High piezoelectric properties of d₃₃=205 pC/N, k_p=38.0%, Q_m=119, ɛ₃₃^T/ɛ₀=1254, and tan δ=0.0264 are obtained for a KNN‐BT‐2wt% (B₂O₃–CuO) sample sintered at 1120°C.