Study On The Properties And Doping Modification Of PMN-PNN-PZT Quaternary Piezoelectric Ceramics

0.25Pb(Mg_1/3Nb_2/3)O₃-0.15Pb(Ni_1/3Nb_2/3)O₃-(0.6-x)PbZrO_3-xPbTiO₃ (abbreviated as PMN-PNN-PZT) piezoelectric ceramics was selected as research object, the effect of Ti/Zr ratio on its morphotropic phase boundary ,dielectric and piezoelectric properties was studied.The results show that the system lies in morphotropic phase boundary when Ti/Zr ratio is between 1.55 and 1.655,while rhombohedral phase transforms into tetragonal phase.The best properties are abtained when Ti/Zr=1.643:ε₃₃^T/ε₀=3380,d₃₃=477pC/N,K_p=0.56,Q_m=82, tanδ=2.3%,T_c=205℃.In the paper, the effect of precursor synthesis process compared with oxide compound synthesis process on phase structure, microstructure and properties of PMN-PNN-PZT ceramics was investigated.The experiment indicates that the precursor synthesis process can avoid Pyrochlore Phase, stabilize the chemistry matching,inhibit the big grain growth and improve sintering densities, the material properties can be improved greatly by the process.Also,the effect of sintering temperature on microstructure and material properties was discussed,it is found that, sintered at 1180℃,the crystals is dispersive well ,the average grain size is (3～5)μm and the biggest volume density is 7.89g/cm³ ,while the porosity is lowest, 3%.In the end, the doping modification of PMN-PNN-PZT system piezoelectric ceramics was studied. Some conclusions can be drawed by analyzing the influence of the oxide dopants as La₂O₃,ZnO and CeO₂ upon the material properties,also combining SEM and XRD pictures: the optimal doping amount of La₂O₃,ZnO and CeO₂ is 0.6wt%,0.4wt% and 0.10wt% respectively.Excessive amount of dopants will assemble in the crystal boundary and influence material properties.The material properties can be improved obviously with 0.10wt% CeO₂ doping compared with other dopants:ε₃₃^T/ε₀=3640,d₃₃=507pC/N,K_p=0.61,Q_m=116,tanδ=1.0%,T_c =222℃.The CeO₂ doping can promote crystal grain growth, the biggest crystal grain diameter can attain 20μm.The behavior effect of CeO2 doping on material properties are explained by soft doping and hard doping mechanism.