Abstract
It is a very difficult work to sinter K0.5Na0.5NbO3 (KNN)-based materials with good reduction resistance in strong reducing atmosphere. 0.945K0.48Na0.52Nb0.96Ta0.04O3−0.055BaZrO3 + 0.03ZrO2 + y mol%MnO (KNNT−0.055BZ + 0.03Zr + yMn) ceramics sintered in reducing atmosphere were prepared successfully by conventional solid-state reaction methods. MnO dopant increases grain size at y = 5–8 due to strong lattice distortion and then decreases grain size at y = 9 due to much Mn4Nb2O9 accumulated at the grain boundary. MnO dopant as an excellent sintering aid can effectively reduce volatilization of alkali metal by decreasing the sintering temperature (Tsinter). Reducing alkali metal volatilization can greatly reduce oxygen vacancies and improve piezoelectric properties. MnO dopant can improve the anti-reduction properties. The KNNT−0.055BZ + 0.03Zr + yMn ceramics at y = 6–9 show outstanding anti-fatigue of unipolar piezoelectric strain under the synergistic effect of reduced oxygen vacancies due to reduced volatilization and increased grain size. Piezoelectric properties and temperature stability of KNNT−0.055BZ + 0.03Zr ceramics sintered in reducing atmosphere are improved simultaneously by MnO dopant. Optimum inverse piezoelectric coefficient (d33*) of ceramics at y = 8 reaches up to 480 pm/V under low driving electric field E = 20 kV/cm at room temperature, and its temperature stability of d33* reaches 158 °C. It will be an excellent lead-free material candidate for the preparation of multilayer piezoelectric actuators co-fired with nickel electrode.
Highlights
A great deal of attention for the lead-free piezoelectric materials was recently given to the Na0.5K0.5NbO3(KNN)-based ceramics due to the excellent piezoelectric properties and environmental friendliness [1]
The ΔT decreases from 20 to 10 °C, which suggests the effect of MnO as a sintering aid is weakening and the negative value (−10 °C) of ΔT appears at y = 9
Lead-free KNNT–0.055BZ + 0.03Zr + yMn ceramics sintered in reducing atmosphere were prepared by conventional solid-state reaction methods
Summary
A great deal of attention for the lead-free piezoelectric materials was recently given to the Na0.5K0.5NbO3. The multilayer design of piezoelectric materials brings great hope for the application of lead-free piezoelectric materials It means that multilayer structure design can make up for the lack of piezoelectric strain for KNN-based ceramics. When KNN-based ceramics are sintered in high temperatures, the irreversible volatilization of alkali metals can result in the formation of oxygen vacancy (marked as Vo (II) ). In KNN-based ceramics, the oxygen vacancies will affect fatigue properties, temperature stability, and piezoelectric properties. B-site, we believe that Mn ion doping is very likely to control or decrease the oxygen vacancy in ceramics, improving the fatigue properties, temperature stability, and piezoelectric properties. The KNNT–0.055BZ + 0.03Zr + yMn (yMn: y mol% MnO) ceramics at y = 6–9 show outstanding anti-fatigue of unipolar piezoelectric strain (β > 94%) under the synergistic effect of reduced oxygen vacancies due to reduced volatilization and increased grain size
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