Defect control for enhanced piezoelectric properties in SnO2 and ZrO2 co-modified KNN ceramics fired under reducing atmosphere

The additions of SnO2 and ZrO2 are beneficial to improve the piezoelectric and dielectric properties of the reducing atmosphere fired (K0.5Na0.5)NbO3-based ceramics. The degradation of electrical properties when the pure (Na0.52K0.45Li0.03)NbO3 ceramics sintered in reducing atmosphere is mainly caused by the increasing of oxygen vacancy concentration, as low oxygen partial pressure promote the formation of oxygen vacancy. The 0.3 mol% SnO2 and 0.3 mol% ZrO2 co-modified ceramics sintered in reducing atmosphere exhibit excellent electrical properties (d33 = 198 pC/N, kp = 31.5%, ε33T/ε0 = 304, and tanδ = 0.022), which are comparable to the air fired ceramics with the same composition (d33 = 206 pC/N, kp = 32.6%, ε33T/ε0 = 590, and tanδ = 0.020). By thermally stimulated depolarization current technique, it can be demonstrated that the reduced fired doped ceramics have similar concentration of oxygen vacancy and defect dipole with the air fired ceramics due to the substitution of Sn and Zr into the A-sites and B-sites of perovskite structure. This study not only demonstrate the Sn and Zr co-doped KNN-based systems could possibly co-fire with base metal inner electrode but also broaden the selection of low-cost and eco-friendly materials for multilayer piezoelectric devices.