Improving piezoelectric properties and temperature stability for KNN-based ceramics sintered in a reducing atmosphere

Lead-free 0.955K0.5Na0.5Nb1-zTazO3-0.045Bi0.5Na0.5ZrO3+0.4%MnO ceramics (abbreviated as KNNTaz-0.045BNZ+0.4Mn) were prepared by a conventional solid-state sintering method in a reducing atmosphere (oxygen partial pressure of 1 × 10−10 atm). All ceramics with a pure perovskite structure show the two-phase coexistence zone composed of rhombohedral and tetragonal phase. Ta5+ ions substitute for Nb5+ ions on the B-site, which results in a decrease in the R phase fraction in the two-phase coexistence zone. The R-T phase transition temperature moves to room temperature due to the substitution of Nb5+ ions by Ta5+ ions. A complex domain structure composed of small nano-domains (~70 nm) formed inside large submicron domains (~200 nm) exists in KNNTa0.02-0.045BNZ+0.4Mn ceramics, which can induce a strong dielectric-diffused behavior and improve the piezoelectric properties. The temperature stability for the reverse piezoelectric constant (Formula presented.) for the KNNTaz-0.045BNZ+0.4Mn ceramics can be improved at z = 0.02. Excellent piezoelectric properties (d33 = 328 pC/N, and (Formula presented.) = 475 pm/V at Emax = 20 kV/cm) were obtained for the KNNTa0.02-0.045BNZ+0.4Mn ceramics. © 2018 The American Ceramic Society