Phase Boundary Construction And Electrical Properties Of Potassium Sodium Niobate-based Lead-free Piezoelectric Ceramics

With the development of industry,piezoelectric ceramics are widely used in military and civilian products,especially lead-based piezoelectric ceramics due to its thermal stability and excellent piezoelectric properties,which can be used as sensors,transducers,Ultrasonic motors and other devices.However,due to the harm of lead to the environment and the human body,some organizations and countries have gradually banned the used of lead.Therefore,replacing lead-based ceramics with lead-free piezoelectric ceramics has become one of the current research hotspots in the field of piezoelectric ceramics.Among them,potassium sodium niobate(KNN)lead-free piezoelectric ceramics are considered to be one of the most likely alternative materials to replace lead-based ceramics due to their high Curie temperature and adjustable performance.In this paper,potassium sodium niobate(KNN)is used as the matrix,and the polycrystalline phase boundary is constructed by doping to improve its piezoelectric performance,and the performance enhancement mechanism is systematically analyzed.Specific research contents and summary are as follows:1.Firstly,the doping experiment of replacing expensive Bi with cheap Al was studied.(1-x)K0.5Na0.5Nb0.965Sb0.035O3-x(Bi0.82Al0.18)0.5Na0.5Zr O3(x=0.02?0.03?0.04and 0.05)were prepared by solid-state method.The XRD analysis results show that with the increase of x,the ceramic undergoes a phase transition from orthogonal(O)to tetragonal(T),and its piezoelectric properties are improved(d₃₃?258 p C/N,k_p?0.40).According to the variation of the Raman displacement of the characteristic vibration mode,the role of small radius ions in the deformation of the KNN lattice is studied,and the lattice deformation and the related phase evolution process are qualitatively deduced.2.On the basis of experiment 1,the formula was further adjusted,and0.955(K_0.5Na_0.5)(Nb_0.965Sb_0.035)O₃-0.045(Bi_1-xAl_x)Na_0.5Zr O₃(x=0.08?0.1?0.12?0.14?0.16?0.20)was prepared by solid-phase method.When x=0.1,a rhombohedral(R)-tetragonal(T)phase boundary and a unique domain structure are formed in the ceramic,which promotes irreversible non 180°domain movement,and makes the ceramic obtain excellent electrical properties(d₃₃?570 p C/N,k_p?0.60),and ceramics have a high Curie temperature(T_c?280?)and low loss(tan??0.28%).3.Based on the previous experiments,the effects of doping substitution of A and B on the properties of ceramics were further studied.The ceramic(1-x)K0.5Na0.5Nb0.965Sb0.035O3-x(Bi0.9Al0.1)0.5Na0.5Zr0.42Hf0.58O3(x=0,0.01,0.02,0.03,0.04,0.045 and 0.05)were prepared by solid state method.The results of XRD refinement,Raman spectroscopy,transmission electron microscopy and dielectric temperature curve analysis show that with the increase of x,the ceramics form rhombohedral-tetragonal(R-T)phase coexistence when 0.04?x?0.05.Under the combined action of the inverse non 180°domain motion,the ceramics show excellent performance when x=0.045 Piezoelectric properties(d₃₃?451 p C/N,d^*₃₃?404 pm/V;k_p?0.46).4.Superfine BiFeO₃ particles were synthesized by hydrothermal method at 180?/6h.Then(1-x)K_0.5Na_0.5Nb_0.965Sb_0.035O₃-x BiFeO3(x=0;0.001;0.002;0.003;0.004;0.005;0.006;0.007 and 0.008)ceramics were prepared by adding nano BiFeO₃ particles into K_0.5Na_0.5Nb_0.965Sb_0.035O₃ ceramics.The microstructure and electrical properties of ceramics were systematically studied,and the mechanism of the remarkable improvement of ceramic properties was deeply analyzed.The results show that that rich T phase is beneficial to improve the properties of the ceramics.In addition,the energy band structure of ceramics should be compared with the conventional solid phase through the above method,and the results show that the ceramic of the above method generates a Schottky barrier at the KNNS and BF interface,which promotes domain rotation.In summary,the piezoelectric properties(d₃₃?220 p C/N and k_p?0.46)are superior to those of traditional solid-state reactions(d₃₃?161 p C/N and k_p?0.39)because the electric domain is more easily moved.