Preparation,structure And Electrical Properties Of Potassium Sodium Niobate Based Lead-free Piezoelectric Ceramics

Lead based（PZT）piezoelectric materials have been widely used in various electronic devices due to their excellent electrical properties.However,lead element toxicity,high performance of lead-free piezoelectric materials has become a research hotspot.Among them,potassium sodium niobate based lead-free piezoelectric ceramics is a promising alternative to lead-free piezoelectric materials because of its excellent piezoelectric properties and high Curie temperature.Therefore,this paper takes potassium sodium niobate based lead-free piezoelectric ceramics as the research object,through the composition design,the research work is carried out from two aspects of new phase boundary construction and preparation process.The specific research results are as follows:（1）(K_0.48Na_0.52)_1-xL i_x Nb O₃ ceramic samples were prepared by the traditional solid-state sintering method,and the effect of Li⁺addition on the microstructure and electrical properties of KNN-based ceramics was studied.The results show that Li⁺addition can reduce the O-T phase transition temperature and build O-T phase boundary in KNN based ceramics,and improve the electrical properties of KNN based ceramics;at the same time,Li⁺addition can improve the density and Curie temperature of ceramic samples.Near the O-T phase boundary,The samples with x=0.06 possesses the optimum piezoelectric properties:d₃₃～190 p C/N,k_p～0.401,S_max～0.071%,d^*₃₃～223 pm/V,_CT～455℃.（2）（1-x）(K_0.48Na_0.52)_0.935Li_0.65Nb O₃-x Ba Zr O₃ceramic samples were prepared by the traditional solid-state sintering method.Research shows that when x=0.06,the R-T phase boundary coexists at room temperature,and the sample possess the optimum properties,d₃₃～207 p C/N,k_p～0.3 02,in addition,0.94(K_0.48Na_0.52)_{0.9 35}L i_0.65Nb O₃-0.06Ba Zr O₃ were prepared by three-step sintering method.It is found that the three-step sintering method can make the ceramic sample obtain more compact structure and more uniform grain size.At the same time,according to the impedance spectrum analysis,when the three-step sintering method is used to prepare the ceramic,the sample has less oxygen vacancy.When the sintering condition is 1050℃-1150℃/5min-1070℃/20h,the possesses the optimum properties:ρ（28）4.51 g/cm³,d₃₃～258 p C/N,k_p～0.3 49,_CT～328℃.（3）（0.996-x）(K_0.48Na_0.52)Nb O₃-0.004Bi Co O ₃-x Bi_0.5Na₀.₅Hf O₃ ceramic samples were prepared by the traditional solid-state sintering method.By constructing R-O-T phase boundary in KNN based ceramics,the properties of KNN based ceramics can be improved.At the same time,the Curie temperature of KNN based ceramics can be improved by adding Bi Co O₃ with high Curie point.The results show that the samples with x=0.035 possesses the optimum properties:d₃₃～272 p C/N,k_p～0.4 71,S_max～0.145%,d^*₃₃～358pm/V,T_C～333℃.