Sintering and piezoelectric properties of KNN ceramics doped with KZT

This paper investigates the effect of K_1.94 Zn_1.06Ta_5.19O₁₅ (KZT) addition on the sintering behavior and piezoelectric properties in lead-free piezoelectric ceramics of (K_0.5Na_0.5)NbO₃ (KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsiv₃ ^T/epsiv₀ = 590, d₃₃ = 126 pC/N, k_p = 0.42, and P_tau, = 18 muC/cm² were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (~0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for den-siflcation. A small amount of KZT was effective for den-siflcation of KNN ceramics by promoting K_5.75Nb_10.8O₃₀ liquid phase formation. However, even though KNN with 1.0~2.0 mol% KZT had a relative density of > 98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.