Investigation On The Structure And Electrical Properties Of Element-doped （K,Na）NbO₃ And （Bi,Na）TiO₃ Based Piezoelectric Ceramics

Lead-based piezoelectric materials are widely used in military industry and daily life due to their excellent piezoelectric properties and stable chemistry.However,the producting,using and post-processing of lead-based products will cause harm to the environment and human health.Therefore,some researchers are trying to explore a high-performance lead-free piezoelectric material to replace the lead-based materials.(K_0.5Na_0.5)Nb O₃（KNN）and(Bi_0.5Na_0.5)Ti O₃（BNT）based lead-free piezoelectric ceramics have excellent electrical properties,which makes it possible for lead-free piezoelectric ceramics to replace lead-based ceramics.In this paper,we choose KNN and BNT based piezoelectric ceramics as the research object to prepare multiple lead-free piezoelectric ceramics by constructing a new type solid solution,improving the performance of ceramic,exploring the multifunctional ferroelectric ceramics and other aspects.And we studied the relationship among the phase transition,microstructure and electrical properties.The main research contents and results are as follows:First,we prepared the（1-x）Bi_0.5(Na_0.48K_0.52)_0.5Ti O₃-x Ba ZrO₃ceramics by the solid-phase reaction method（aliased as（1-x）BNKT-x BZ）.It was found that all the samples exhibited the perovskite structure,indicating that the Ba²⁺and Zr⁴⁺ions entered the lattice gap and formed a stable solid solution.It was found that the average grain size of the sample gradually increased with the increase of the doping amount of BZ.Compared with pure BNT ceramics,the introduction of BZ could effectively optimize the electrical properties of（1-x）BNKT-x BZ ceramics.The maximum polarization temperature and the dispersion index of the samples were systematically studied by the modified Curie Weiss law,and the behavior of the negative temperature coefficient for this ceramic is observed by impedance spectroscopy,which is similar to that of a semiconductor.After adjusting the concentration ratio,the best performance parameters were obtained when the ceramics with x=0.06,ε_m=4624,tanδ=0.0028,T_d=51°C,T_m=352°C.Hence,our results indicate that the ceramic can be a promising candidate for high-temperature superconductor applications.Second,we synthesized the（1-x）(K_0.48Na_0.52)Nb_0.96Sb_0.04-x(Bi_0.45Sm_0.05Na_0.5)ZrO₃ceramics with Sm³⁺-doped to improve the properties of the KNN-based ceramics.And by means of XRD,SEM,Raman,dielectric temperature spectrum and PL,the relevant properties such as piezoelectricity,dielectricity,ferroelectricity,and fluorescence property were discussed at length.It was found that for x=0.03～0.04,the R-T phase boundary can be successfully constructed and the two-phase coexistence illustrates relatively superior comprehensive properties(d₃₃=260 p C/N,ε_r=2185,T_C=250 ^oC,P_r=21μC/cm²,E_c=15 k V/cm).Meanwhile,the KNNS-x BSNZ ceramics shows good photoluminescence characteristics at room temperature,which can achieve the combination of the piezoelectric and luminescent properties.Hence,we believe that this work have important reference value for the popularization of the optoelectronic components and multifunctional applications.Third,we choose the SrTiO₃ which has the ABO₃ type perovskite structure as the dopant,and the（0.97-x）(K_0.47Na_0.50Li_0.03)(Nb_0.96Sb_0.04)O₃-0.03(Bi_0.45Na_0.5Sm_0.05)ZrO₃-x SrTiO₃ ternary lead-free piezoelectric ceramic system was prepared.The sintering characteristics,phase structure,microstructure and electric properties of（0.97-x）KNNLS-0.03BSNZ-x ST ceramics were studied.The result shows that the introduction of ST can construct the O-T coexisting phase region in the ceramics,which could lead the increasing of the direction of spontaneous polarization and the probability of domain reversal,thus affecting the mechanical and electrical properties of the materials.With the component of x=0.001,the ceramics show the best performance,d₃₃=298 p C/N,ε_RT=1991,ε_m=7046,T_C=287 ^oC,P_r=17μC/cm²,E_c=14 k V/cm.The excellent electrical properties of the ceramic system make it possible to be used in high performance capacitive materials.