Ultrahigh electric-field-induced strain in KNN-based piezoelectric ceramics sintered in reducing atmosphere

With the goals of sustainable development adopted by more and more nations, the lead-free trend of multilayer ceramic actuators has become a widely recognized consensus. Sintering in a reducing atmosphere is a necessary approach for preparing lead-free ceramics co-fired with low-cost nickel internal electrodes. Herein, (1 − x )K 0.48 Na 0.52 Nb 0.96 Ta 0.04 O 3 – x Sr(Zr 0.5 Ti 0.5 )O 3 + 0.03ZrO 2 + 0.08MnO 2 (KNNT-SZT) ceramics were sintered in a reducing atmosphere using a solid-state reaction. The Sr(Zr 0.5 Ti 0.5 )O 3 (SZT) dopant decreased the Curie temperature T C and the O–T phase transition temperature. The enhanced diffuseness of the ferroelectric phase transition of KNNT-SZT ceramics is attributed to the element doping and the locally inhomogeneous microstructure. High inverse piezoelectric coefficients d 33 * of 883 and 787 pm/V were obtained for the 8- and 9-mol% SZT-doped samples, respectively. These results were attributed to the synergistic effect of ferroelectric domains with different sizes. The diffused O–T phase transition significantly improved the piezoelectric temperature stability of the 9-mol% SZT-doped sample, whose electric-field-induced strain decreased by <10% from room temperature (25°C) to 115°C. The cyclic fatigue test showed that >98% of the initial d 33 * was retained after 10 6 cycles of unipolar electrical loading. The KNNT-SZT ceramics sintered in a reducing atmosphere possessed excellent inverse piezoelectric properties and are expected to be applied in the field of multilayer ceramic piezoelectric actuators with base metal internal electrodes.