Simultaneously improving piezoelectric properties and temperature stability of Na0.5K0.5NbO3 (KNN)-based ceramics sintered in reducing atmosphere

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 (d 33 * ) 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 d 33 * reaches 158 °C. It will be an excellent lead-free material candidate for the preparation of multilayer piezoelectric actuators co-fired with nickel electrode.

Ultrahigh electric‐field‐induced strain in KNN‐based piezoelectric ceramics sintered in reducing atmosphere

“…The d 33 * values of the KNNT‐SZT ceramics under an electric field of 2 kV/mm at different temperatures were measured, and the ratio of d 33 * at temperature T to d 33 * at room temperature (25°C) is plotted in Figure 7A. When d 33 * at temperature T drops below 90% of d 33 *(25°C), the material is typically considered to have lost the temperature stability of the inverse piezoelectric property, and the corresponding temperature can be labeled T e to indicate the range of temperature stability 27,29 . Another temperature index T d known as the depolarization temperature is shown in Figure 7A.…”

“…In this study, SZT was doped at different contents into KNN‐based piezoelectric ceramics to form PPB. Excess Zr was added to improve system stability in a reducing atmosphere, 28 and excess Mn was added to decrease the sintering temperature and oxygen vacancies 29,30 . The inverse piezoelectric properties, temperature stability, and fatigue performance of the prepared KNN‐based ceramics with different SZT contents were studied.…”

“…Excess Zr was added to improve system stability in a reducing atmosphere, 28 and excess Mn was added to decrease the sintering temperature and oxygen vacancies. 29,30 The inverse piezoelectric properties, temperature stability, and fatigue performance of the prepared KNN-based ceramics with different SZT contents were studied. The origin of the piezoelectric properties of the phase structure and micromorphology was analyzed.…”

Enhanced Thermal Stability in Dielectric Properties of NaNbO3–Modified BaTiO3–BiMg1/2Ti1/2O3 Ceramics for X9R-MLCC Applications

“…High ε r dielectrics are preferred for capacitors and there are some promising lead-based ceramics that have a high ε r value in the range of 10,000-25,000, such as Pb(Fe 1/3 W 2/3 )O 3 , Pb(Mg 1/3 Nb 2/3 )O 3 and Pb(Zn 1/3 Nb 2/3 )O 3 but lead is considered toxic and hazardous to human health [16][17][18][19][20][21][22][23]. Therefore, the use of lead is constrained by the European Union.…”

Enhanced piezoelectric property in Mn‐doped K0.5Na0.5NbO3 ceramics via cold sintering process and KMnO4 solution

“…First, the addition of appropriate Mn can enhance the dielectric constant (ε r ) and then improve the piezoelectric coefficient (d 33 ). 11,12 On the other hand, high-content Mn doping can form the defect dipoles and show pinning effect on the movements of domain walls, 9,[13][14][15] which can improve the electric field-induced strain and mechanical quality factor (Q m ), and reduce the dielectric loss (tan δ) of KNN-based ceramics. In addition, the introduction of Mn is conducive to grain growth, 9,16 and the large grain size is beneficial to improve the piezoelectric property.…”