Bi-based lead-free ceramic multilayer actuators using AgPd–(Na0.51K0.47Li0.02)(Nb0.8Ta0.2)O3 composite inner electrodes

We investigated the effect of inner electrode composition on the microstructure and electromechanical properties of Bi0.5(Na0.82K0.18)0.5TiO3 (BNKT) multilayer ceramic actuators. Using tape-casting and screen printing techniques, multilayered laminates were prepared by stacking green sheets of Nb-modified BNKT ceramic layers with AgPd (70/30 in weight ratio) thick films as the inner electrode. After co-firing at temperatures of 1100–1140 °C for 4 h in air, the multilayered structure revealed significant camber as well as cracks due to the mismatch in thermal shrinkage between the ceramic and the AgPd layer. However, the addition of 10 wt% (K0.47Na0.51Li0.02)(Nb0.8Ta0.2)O3 (KNLNT) powder into the inner electrode markedly suppressed the generation of co-firing-induced defects. More surprisingly, the normalized electric-field induced strain (Smax/Emax) of BNKT multilayer actuators was enhanced from 110 pm/V to 350 pm/V by adding ceramic KNLNT into the AgPd inner electrode.