Study On The Doping Modification And Micro Mechanism Of KNN Based Lead Free Piezoelectric Ceramics

Lead based piezoelectric ceramics?PZT?have been widely used in the field of piezoelectric,however,the toxicity of lead has limited its development.With the enhancement of people's environmental protection consciousness,lead-free alkaline niobate piezoelectric materials have been paid more and more attention.The piezoelectric material of niobate modified by doping and casting process for preparation has the same performance as PZT.Therefore,The preparation of high performance Sodium Niobate Lead-free Piezoelectric Ceramics is a hot topic now.This paper mainly through doping and two step sintering and casting method to gradually improve the piezoelectric properties of KNN ceramics.The piezoelectric properties of KNN based ceramics can be greatly improved by the coexistence of two phases,and CaTiO₃,BaTiO₃ and Ba Zr O₃ were used to prepare the?0.91-x?K_0.5Na_0.5NbO₃-0.03BaTiO₃-0.06BaZrO₃-xCaTiO₃?Abbreviated as:?0.91-x?KNN-BT-BZ-xCT?.By changing the content of CaTiO₃,the coevolution region of the square phase of the rhombohedral phase was moved to the room temperature,and the properties of the ceramics were enhanced.According to the KNN phase diagram,it is found that the alkali metal is easy to volatilize in the sintering process of the KNN ceramics,and the composition of the components can be separated,so that the doping in the liquid phase can lead to the decrease of the ceramic properties.In the experiment,the two step sintering?TSS?method was used to effectively reduce and prevent the segregation,decrease the grain size and improve the degree of homogenization.In order to further improve the properties of the doped ceramics,?001?-oriented 0.90KNN-BT-BZ-0.01 CT based ceramics were prepared by casting method using NN?NaNb O₃?as template.Through the three element doping modification,because of the quasi homogeneous phase boundary?PPT?,when the x value is 0.01,the piezoelectric and dielectric properties of?0.91-x?KNN-BT-BZ-xCT ceramics reach the best,which is 185PC/N.Compared with SSS?ordinary solid state method?sintered ceramics,the density of TSS sintered ceramics is higher than 3%,and the piezoelectric properties of the ceramics are increased by 18%,which is about 219PC/N.Through the analysis of XRD and EDS phase,the sintered ceramic phase has lower alkali metal loss.In the casting process,the preparation of NN template is very important.Firstly,the precursor BNN was prepared by molten salt method,and then the anisotropic lamellar NaNbO₃ template was prepared by molten salt method and the chemical reaction.When the content of the template was 5%,the properties of the piezoelectric ceramics were the best,and the texture of the prepared f reached to 86%.Compared with the non-textured ceramics,the texture ceramics reduce the axial ratio?c/a?of the ceramics and the Curie temperature region and the dielectric constant peak in the dielectric temperature spectrum curve,which can improve the temperature dependence of the dielectric constant.The piezoelectric ceramics prepared by different methods have the best piezoelectric properties and electromechanical conversion efficiency.d33 and Kp can reach 236PC/N and 42.2%,respectively.