Superior piezoelectric properties of lead-free thick-films and their application to alternative multilayer actuator

CuO-added 0.97(Li_0.04Na_0.46K_0.5)(Nb_0.89Sb_0.11)O₃-0.03CaZrO₃ (CLNKNS-CZ) thick-films synthesized at 1060 °C exhibit a dense microstructure comprising small grains and abnormally grown large grains. They have an orthorhombic-tetragonal polymorphic phase boundary structure and exhibit good piezoelectric properties: d₃₃ = 488 pC/N and k_p = 0.45. They have a large electric-field induced strain (0.16% at 4.0 kV/mm) which was maintained at 100 °C, whereas the strain decreased slightly to 0.15% at 150 °C. Moreover, a large strain was maintained after 10⁶ electric-field cycles with a maximum electric field of 1.0 kV/mm. Hence, CLNKNS-CZ thick-films exhibit thermally stable strain with good fatigue properties. We synthesized multilayer ceramics comprising five layers of CLNKNS-CZ thick-films and 70Ag–30Pd electrodes with sharp interfaces between ceramic layers and electrodes. Cantilever-type CLNKNS-CZ actuators showed a large displacement (2.5 mm) and acceleration (33.4 G) at 25 V, and similar results were obtained via simulation. Furthermore, the actuating properties of CLNKNS-CZ actuators are comparable to those of PZT-based actuators.