Effect Of Component Introduction And Doping Modification On The Properties Of KNN Based Lead-free Piezoelectric Ceramics

At present,the widely used piezoelectric ceramics are lead based piezoelectric ceramics represented by lead zirconate titanate（PZT）.The main components are PbO,PbO is a kind of toxic material,which will cause a lot of lead pollution.Therefore,it is of great social and economic value to study high performance lead-free piezoelectric ceramics.On the other hand,with the rapid development of Aeronautics and Astronautics and medical systems,the pressing demand for piezoelectric functional devices that can work in high temperature environment is put forward.KxNa（1-x）NbO3（KNN）lead-free piezoelectric ceramics have become one of the most potential alternatives for lead based piezoelectric ceramics because of their better piezoelectric properties and higher Curie temperature.In this paper,0.94KNN-0.06LS ceramics is modified by two ways of adding new component and ion doping,the details are as follows,（1）Based on 0.94KNN-0.06LS,0.94KNN-（0.06-x）LS-xBNZ ceramics were prepared by introducing component Bi0.5Na0.5ZrO3（BNZ）.All ceramic samples formed a homogeneous perovskite structure.When x=0.04,the phase structure of the samples is in the rhombohedra-tetragonal phase coexistence of Polymorphic Phase Transition（PPT）,and ceramics have the best electrical properties:d33=286pC/N,kp=42%,ε_r=2400,tanδ=0.044.The electrical properties of ceramics increase significantly,the dielectric relaxation behavior is enhanced,and the Curie temperature decrease slightly,but all above 320℃.It is much higher than that of PZT based piezoelectric ceramics,and is suitable for high temperature applications.（2）On the basis of 0.94KNN-0.02LS-0.04BNZ,the effect of CeO2 doping on its properties was studied.The results show that CeO2 can inhibit the growth of ceramic grains,increase dielectric constant and decrease dielectric loss.When x=0.03%,the comprehensive electrical properties of ceramics are the best:d₃₃=252pC/N,k_p=42%,ε_r=2832,tanδ=0.018.（3）On the basis of 0.94KNN-0.02LS-0.04BNZ,the effect of Sm2O3 doping on its properties was studied.The results show that Sm2O3 can enhance the relaxation behavior of ceramics,the maximum ofγis 1.72559 when x=0.4%,and the relaxation characteristics of ceramics are the strongest.When x=0.3%,the electrical properties of ceramics are the best,d₃₃=242pC/N,k_p=39%,ε_r=2547,tanδ=0.038.（4）On the basis of 0.94KNN-0.02LS-0.04BNZ,the effect of La2O3 doping on its properties was studied.The results show that,compared with undoped,the piezoelectric constant and electromechanical coupling coefficient decrease as a whole.When x=0.1%,ceramics have the best comprehensive electrical properties,d₃₃=255pC/N,k_p=39%,ε_r=2637,tanδ=0.02,dielectric constant increases slightly,dielectric loss decreases significantly,and the decreasing amplitude is up to 50%.（5）On the basis of 0.94KNN-0.02LS-0.04BNZ,the effect of Co2O3 doping on its properties was studied.The results show that Co2O3 can promote grain growth of ceramics as a sintering aid.When x=0.2%,the electrical properties of ceramics are the best,d₃₃=244pC/N,k_p=37%,ε_r=2134,tanδ=0.038,and the dielectric loss slightly decreases.（6）Doping with CeO2,Sm2O3 and La2O3 can can inhibit the growth of ceramic grains and enhance the relaxation behavior of ceramics,and the Curie temperature is above 280℃,which are suitable for the relaxor ferroelectrics in high temperature environment.