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 Bi 0.5 (Na 0.82 K 0.18 ) 0.5 TiO 3 (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% (K 0.47 Na 0.51 Li 0.02 )(Nb 0.8 Ta 0.2 )O 3 (KNLNT) powder into the inner electrode markedly suppressed the generation of co-firing-induced defects. More surprisingly, the normalized electric-field induced strain ( S max / E max ) of BNKT multilayer actuators was enhanced from 110 pm/V to 350 pm/V by adding ceramic KNLNT into the AgPd inner electrode.