Preparation of KNN based lead-free piezoelectric ceramics via composition designing and two-step sintering

0.95(Li0.04Na0.48K0.48)(Nb0.94Sb0.06)O3-0.05(Ba0.5Ca0.5)(Zr0.5Hf0.5)O3 (LNKNbS-BCZH) lead-free piezoelectric ceramics were prepared by the solid-state reaction method via the two-step sintering process. Via composition designing pure perovskite LNKNbS-BCZH ceramics are synthesized, which present complex coexistence of orthogonal and tetragonal ferroelectric phases in rhombohedral matrix and high densification depending greatly on the two-step sintering conditions. Due to the addition of some metal elements and the second component BCZH, there appear dielectric peak at Curie temperature TC/Tm of ∼200 °C and dielectric shoulder around room temperature, and the LNKNbS-BCZH ceramics approach to normal ferroelectrics with some diffused phase transition characteristic. Excellent ferroelectricity and piezoelectricity are obtained via composition designing and two-step sintering, in which the LNKNbS-BCZH ceramics sintered at 1180 °C for 45 min and 1050 °C for 8 h exhibit the largest piezoelectric constant of 232 pC/N, which can be increased further by room-temperature aging and re-poling. The safe working temperature for piezoelectric applications of the LNKNbS-BCZH ceramics should be below 100 °C.