Preparation And Electrical Properties Of Modified Sodium Potassium Niobate-based Lead-free Pizoelectric Ceramics

On the basis of absorbing from previous research results on the improvement of KNN-base lead-free ceramics, three different kinds of modified experiments were designed, including new components and new experiment scheme. The testing methods and theoretical analysis are combined in order to investigate the changes of the lattice constants, microstructure and electric properties with contents.The Rhombohedra-phase BiCoO3(BCO for short) was doped in the Tetragonal-phase (K0.475Na0.475Li0.05)(Nb0.8Ta0.2)03(KNLNT for short), the transformation point Tc of BCO-doped KNLNT got a liner decrease with the increase of BCO and Morphotropic phase boundary was got. The effects of the Morphotropic phase boundary and Polymorphic phase transition both influent the electric properties of the samples. The experiment results show that the grain refinement effect due to BCO and the variety of valence of Co can both significantly reduce the electric properties, deviating from the theory analysis. Prolonging the sintering time can weak the grain refinement effect and improve the electric properties to some extent.Sc is selected to take the place of Co. With the doping of Rhombohedra-phase BiScO3(BSO for short), the transformation temperature Tc was decreasing linearly, the Morphotropic phase boundary was got and the lattice constants were got by the refinement of the lattice constants. Though the ion Sc is more stable than Co, the refinement effect is still found due to the dopant BSO. The method of prolonging the sintering time can make the grain grows to a certain degree. Combing the weakness of the effect of the Polymorphic phase transition and enhance of the effect of Morphotropic phase boundary, the maximum of the electric properties appears in the diagram of the variation tendency of piezoelectric constants.Three sets of experiments were designed including taking CuO as the sintering additives, attempting to take Cu2+to replace the A site elements and B site elements of the ABO3perovsike structure (Cu-Z, Cu-A, Cu-B for short). With the theory analysis of the defect chemistry and the refinement of the lattice constants, we got the conclusion that the change of the lattice volume is not able to be the main way to judge where the Cu2+goes. For Cu-Z set samples, the transformation point TO-T has a tiny left shift compared with pure KNN, CuO shows the effects of the grain growing and optimize the density, but the electric properties hasn’t got any obvious change. For Cu-A set samples, TO-T moves left with the increase of CuO, the microstructure is not change like CuO in Cu-Z set samples, part of the Cu2+begins to replace the B site when x=0.006for showing the double hysteresis loop, the electric property reaches its maximum when x=0.003. For Cu-B set samples, with the CuO doping, TO-T moves left, part of the CuO influence the microstructure like sintering additives, the best electric property shows when x=0.003. Using the way dividing the experiment into three parts can help future research on the effects of CuO in the area of modified KNN-base ceramics.