| The piezoelectric ceramic materials possesses excellent properties,and are widely used in piezoelectric ceramic igniter,piezoelectric transformer,piezoelectric ceramic pickup and loudspeaker etc.At present,it is the most widely used lead based piezoelectric ceramic materials,but the lead based piezoelectric ceramic materials can generate lead toxicity in the process of production and it is harmful to human health and the environment.So many countries have imposed a ban on the use of lead based ceramics.Therefore,the development of new lead-free piezoelectric ceramics has attracted the attention of scholars and researchers from all over the world.In this paper,all the samples were prepared by the traditional solid state sintering method,and their piezoelectric properties were systematically studied.Frist,we investigated the effects of Sb5+ on the phase structure,microstructure and electrical properties of KNN piezoelectric ceramics.The results of XRD patterns and microstructure analysis results and it shows:It is range of the Sb5+ doping content when x=0.02?0.03,the samples were pure perovskite structure,with the increase of doping amount and when it is more than 0.03,the samples appeared in the second phase structure;and Sb5+ could effectively improve the solid solubility between KNbO3 and NaNbO3;at the same time with the increase of the Sb5+ content,the sample was transformed from orthorhombic phase to tetragonal phase structure,further increases with the Sb5+ doping content,the sample starts to change to pseudo cubic.With the increase of the sintering temperature,the grain size of the samples decreases first and then increases,which indicates that the Sb5+ has the effect of sintering to a certain extent.When the sintering temperature is 1060 ?,the grain size of the sample is uniform,the arrangement is compact,and the porosity is low.KNN ceramic samples sintered at 1060?and Sb5+ doping content of x=0.02 when the best comprehensive performance of d33=98CP/N;Qm=2456;kp=0.3229;?r;tan? =0.7836%.Then,the effects of the second component BaTiO3 in the KNN based piezoelectric ceramics were studied.The results of XRD patterns and microstructure analysis and it shows:it less of the BaTiO3 doping content,the second phase structure appears in the sample.With the increase of doping content,the solid solubility of solid solution between BaTiO3 and KNN increases,and the second phase disappears when x=0.03.And with the increase of the doping content,there is a transition between orthorhombic and tetragonal phase.The samples were sintered at 1080? and the doping content x=0.02,the best grain distribution was obtained,the grain size was uniform,the arrangement was relatively tight,and the porosity was low.The best comprehensive properties of 0.98KNN-0.02BT ceramic samples sintered at 1080?:d33=108CP/N;Qm=852.29;kp=0.3;?r=1421;tan?=0.528%.On the basis of the second part,we studied the phase structure,microstructure and electrical properties of MnO2 doping.The results are show:the solubility of MnO2 in perovskite crystal structure is small.When the MnO2 doping content is overdose,the impurity phase appears in the sample.When MnO2 was doped in a small amount,the Mn4+ enter into the lattice completely,which is characterized by the "acceptor" doping.However,when the MnO2 is doped,it plays the role of sintering additives.When x=0.01,the sample is pure perovskite structure.When the doping content of MnO2 when x=0.01?0.03 range and the sintering temperature is 1080?,the samples with clear boundaries,closely arranged,smaller porosity.The samples were sintered at 1080? and the best performance was obtained when the doping content was x=0.03:d33=159CP/N;Qm=3435:kp=0.2415;?=701.9;tan? =0.4068%.Finally,we studied the effect of LiNbO3 doping in the phase structure,microstructure and electrical properties of KNN based piezoelectric ceramics.The results are show:the second phase of the diffraction peak appeared after the samples doped with LiNbO3,and with the increase of LiNbO3 doping content,changed the orthorhombic tetragonal between the two samples,and with the further increase of LiNbO3 doping content,the transition between tetragonal phase pseudo cubic phase in the samples.With the increase of LiNbO3 content,the grain size gradually increases,and the samples appear porosity and other defects when x=0.03,and with the increase of the content of LiNbO3 doped samples appeared in the grain boundary was not clear phenomenon when x=0.02,the samples were obtained the best comprehensive performance:d33=116 PC/N;kp=0.326;Q,=2191;?r=699:tan? =0.324%. |
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