High-performance (K,Na)NbO₃-based multilayer piezoelectric ceramic actuators with nickel inner electrodes

Multilayer ceramic actuator (MLCA) has been widely employed in actuators due to the large cumulative displacement under the low driving voltage. In this work, the MLCA devices consisting of a lead-free MnCO₃- and CuO-doped 0.96(K_0.48Na_0.52)(Nb_0.96Ta_0.04)O₃–0.04CaZrO₃ piezoelectric ceramics and a base nickel (Ni) metal inner electrode were well co-fired by the two-step sintering process in a reducing atmosphere. The ceramic layer/electrode interface is well-integrated and clearly continuous without distinct interdiffusion and chemical reaction, which is beneficial to the electrical reliability of the MLCA. As a result, the MLCA laminated with nine active ceramic layers obtains an ultrahigh piezoelectric coefficient d₃₃ of 3157 pC/N, about 9 times than bulk ceramics. The 0.5 mm-thick MLCA composed of a series of ~50 μm-thick ceramic layers and ~3 μm-thick Ni electrodes reaches a high 1.8 μm displacement under the low applied voltage of 200 V (the same displacement requires a voltage as high as 3700 V for ~1 mm-thick bulk ceramics). The excellent electrical performance and low-cost base electrode reveal that the (K,Na)NbO₃ (KNN)-based MLCAs are promising lead-free candidate for actuator application.