Improving the piezoelectric strain and anti-reduction properties of K0.5Na0.5NbO3-based ceramics sintered in a reducing atmosphere

Abstract

Lead-free 0.945K_0.48Na_0.52Nb_0.96Ta_0.04O₃-0.055BaZrO₃ + 6%MnO + xZrO₂ piezoelectric ceramics sintered in a reducing atmosphere were prepared by conventional solid-state reaction methods. The use of the ZrO₂ dopant resulted in an increase in the rhombohedral (R) phase in orthorhombic (O)/R coexisting phases. Nonstoichiometric ZrO₂ dopant addition could effectively improve the anti-reduction properties of KNN-based ceramics via controlling the oxygen vacancy concentration. In particular, 2% mol nonstoichometric ZrO₂ dopant addition could improve the activation energy of the grain boundary (E_gb) via increasing the grain boundary thickness. The addition of the ZrO₂ dopant could improve the fatigue resistance of the unipolar piezoelectric strain of 0.945K_0.48Na_0.52Nb_0.96Ta_0.04O₃-0.055BaZrO₃ + 6%MnO ceramics. The optimum inverse piezoelectric coefficient of ceramics at x = 0.01 reached up to ∼465 pm V⁻¹ at a low driving electric field E of 20 kV cm⁻¹ at room temperature, and the temperature stability of reached 155 °C. After 10⁶ unipolar fatigue cycles, the β value of 0.945KNNT-0.055BZ + 6Mn + xZr ceramics could be preserved to more than 86%. The 0.945K_0.48Na_0.52Nb_0.96Ta_0.04O₃-0.055BaZrO₃ + 6%MnO + xZrO₂ ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.