The Research On Electrical Properties Of Bi-Based Composite Perovskite Doped (K_0.5Na_0.5)NbO₃ Lead-Free Dielectric Ceramics

With the development of electronic equipment to the direction of lightweight,low cost and high quality,the corresponding components should have the characteristics of miniaturization,high performance,low cost and environmental friendliness.Potassium niobate sodium based lead-free dielectric ceramic is a kind of environmentally friendly electronic materials.High comprehensive performance,such as,high Curie temperature,provides a possible to achieve the dielectric temperature stability of the wide range,which makes the multilayer ceramic capacitors（‘‘MLCC’’in English in the field）to use the high temperature applications.So many researchers are focusing on promoting the development of this field.However,the volatilization of metal elements（K,Na）at high temperature will induce the decrease of performance,so it is urgent to improve the electrical performance of KNN.In this paper,Bi(Cu_2/3Nb_1/3)O₃（BCN）,Bi(Ni_2/3Nb_1/3)O₃（BNN）,Bi(Ni_3/4W_1/4)O₃（BNW）,Bi(Mg_3/4Mo_1/4)O₃ and Bi(Li_1/3Ti_2/3)O₃（BLT）bismuth-based composite perovskite compound were designed and doped into KNN-based lead-free dielectric ceramics.The ceramics were prepared by a traditional solid-phase sintering method.The microstructure,dielectric properties and impedance properties of ceramic samples were investigated systematically.（1）The phase structures are of BCN,BNN,BNW,BMM and BLT doped KNN ceramics are the single perovskite structures without the formation of the second phase,indicating that these kinds of dopants form solid solution with KNN..The SEM pictures show that the crystals of ceramic grow well.（2）0.99KNN-0.01BCN ceramics in the temperature range 120oC to 342oC had high dielectric constantε_r¹502,low dielectric loss tanδ≤0.035,good temperature stabilityΔε/ε_120°C≤±15%.The maximum piezoelectric constant could reach 131pC/N,and good ferroelectric performances were obtained.Within 132oC to 346oC,0.99KNN-0.01BNN ceramic exhibited highε_r¹657,Δε/ε_132°C≤±10%,tanδ≤0.037in the temperature range of 132°C³46°C.In addition,the impedance spectrum of（1-x）KNN-xBNN ceramics indicates that the resistance of ceramic materials is mainly contributed by the grain.（3）0.99KNN-0.01BNW ceramics with highε_r¹590（140oC to 350oC）,Δε/ε_140°C≤±15%,tanδ≤0.04 in 140°C⁴11°C were obtained.Within the range of123oC to 348oC,0.99KNN-0.01BMM ceramic exhibited good properties withε_r¹418,Δε/ε_123°C≤±15%,tanδ≤0.036（109°C³48°C）.The impedance spectra of the two groups of ceramics also show that oxygen vacancy is a possible motion channel for ion carriers.（4）As x=0.01,the 0.99KNN-0.01BLT ceramics have performances withε_r¹551,Δε/ε_110°C≤±9%,tanδ≤0.036 in the range of 110oC to 330oC.Besides,the ceramics exhibited the maximum piezoelectric constant of 145 pC/N.Impedance spectroscopy indicates that oxygen vacancy is a possible motion channel for ion carriers.Based on the above results,it can be seen that bismuth-based composite perovskite compounds doped KNN lead-free dielectric materials are good candidates for high temperature devices.