| Piezoelectric ceramics have been widely used in the piezoelectric material field, but most of them are lead oxide-based piezoelectric ceramics. Lead oxide dust in the preparation process and the volatile out of lead in the process of high temperature synthesis and sintering are harmful to the environment and humans. Therefore, it is imperative to research and develop the lead-free piezoelectric ceramics. K0.5Na0.5NbO3 has been considered as a good candidate for lead–free piezoelectric ceramics due to its good piezoelectric properties.At first, the K0.5Na0.5NbO3 nano-powders were prepared by mixed hydroxide method. The phase structure and microstructure were investigated. The rod-like grain of the sample is uniform and grain boundary is clear.In this paper, 0.98KNN-0.02BNT-xST and 0.98KNN-0.02BNT-xBT ceramics were synthesized by traditional sintering process and effects of the SrTiO3 and BaTiO3 amounts on phase structure, microstructure density and electric properties of KNN-BNT were investigated. X–ray diffraction (XRD) results showed that the two kinds of piezoelectric ceramics samples can not form pure perovskite phase with SrTiO3 or BaTiO3 under the condition of 1080℃. And with the increase of doping, the sample gradually changed from the tetragonal phase to orthorhombic phase. The 0.98KNN-0.02BNT-xBT lead free ceramics exhibits excellent piezoelectric properties with x=0.05, d33 = 157 pC/N, tanδ= 0.044,εr = 571, kp = 0.34, Qm = 92.To further improve the electric properties of the ceramics and reduce the sintering temperature, ceramic was investigated by doping metal oxides. First of all, effects of the CuO and MnO2 amounts on phase structure, microstructure density and electric properties of KNN-BNT were investigated. The XRD analysis results showed that all the ceramics were quadrature phase and there is impurity phase appeared and the density decreased due to liquid phase between the grains. Piezoelectric ceramics exhibits an excellent piezoelectric properties with x=1.5 mol%, y = 1 mol%. Effects of sintering temperature were also studied. It was found that grains gradually increasing with sintering temperature increasing. The lead free ceramics exhibits excellent piezoelectric properties under the condition of 1040℃, d33=162 pC / N,εr = 595, tanδ=0.036, kp=0.35, Qm=168. Secondly, effects of the ZnO amounts on phase structure, microstructure density and electric properties of KNN-BNT were investigated. It was found that the crystal structure of the ceramics was perovskite phase with tetragonal phase structure and the density of the samples is less than the undoped ceramic samples. The samples exhibit an excellent piezoelectric properties with x=1 mol%. The impact of its sintering temperature was also studied. It was found that grains of the samples were developed well and the boundary clear under the condition of 1020℃. And the density of the samples reached the maximum. Under optimum conditions the lead free ceramics exhibits excellent piezoelectric properties, d33=138 pC/N,εr =493,tanδ= 0.042,kp=0.32,Qm=159. |
