Study On Preparation And Properties Of Rare Earth Doped PZT-based Relaxor-Ferroelectric Ceramics

Piezoelectric materials are a kind of functional materials with wide range of application,because they can transform mechanical energy into electrical energy,or vice versa.It is the core material of electronic devices such as transducers,drivers,vibration sensors and so on.Lead zirconate titanate（PZT）-based piezoelectric ceramics is the most widely used piezoelectric material on the market nowadays.The modification of PZT-based piezoelectric ceramics to improve its piezoelectric properties has always been a research hotspot in this field.The current development trend of piezoelectric materials is to achieve excellent performance,high sensitivity,good stability,and meet the new needs of integration,multi-function and integration to fit electronic devices.Based on the above background,the ternary lead magnesium niobate-lead zirconate titanate（PMN-PZT）ceramics with excellent piezoelectric properties and good temperature stability was selected as the research system.Through the construction of the morphology phase boundary（MPB）,rare earth Sm doping and the addition of Cu O low-temperature sintering aids,the microstructure and macro-electric properties of the material have been systematically studied.The main contents are as follows:（1）The low PMN content phase boundary of the 0.4%Sm-0.25PMN-x PZ-（0.75-x）PT ternary system was selected as the research system,by constructing a weak relaxor system near the MPB region with different Zr/Ti,and doping of the rare earth Sm to enhance its local structural heterogeneity to achieve a high piezoelectric performance.Result shows the x=0.37 component has obtained with the best electrical properties,and its piezoelectric coefficient d₃₃～824p C/N,dielectric constantε_r～3434,residual polarization P_r～38.7μC/cm²,piezoelectric voltage constant g₃₃～27.1*10^-3 m²/C,electrostrain～0.21%,Curie temperature T_C～178°C.Sample at x=0.37 also has good temperature stability,result shows the variation of electrostrain is less than 5%from room temperature to 150°C,and the variation of piezoelectric coefficient is less than10%from room temperature to 110°C.Therefore,this kind of material is a high-performance piezoelectric material with great application prospects.（2）Through doping different content of Sm into the 0.4%Sm-0.25PMN-x PZ-（0.75-x）PT ceramics at x=0.37 composition,and combining the microstructure and macroscopic properties,it is found that the introduction of Sm will significantly reduce the crystal grain size of the ceramics and gradually destroy the macrodomain structure and increase the number of microdomains.The microdomain can provide a stronger dielectric response,but it will break the macroscopic long-range ferroelectric continuity.Therefore,the introduction of Sm will cause an increase in the macroscopic dielectric constant and dielectric relaxation,however,lower the Curie temperature and remanent polarization.The study shows that,appropriate amount of doping can significantly improve the performance of weak relaxation-ferroelectrics,while excessive doping leads to large-area destruction of long-range ferroelectricity,which will deteriorate the performance.Therefore,adjusting the relationship between the macrodomain and the microdomain in a proper way is the key to promote piezoelectric performance.（3）Cu O was chosen as the low-temperature sintering aid to study the influence of different Cu O content on the sintering temperature,structure and properties of 0.4%Sm-0.25PMN-0.37PZ-0.38PT ceramics.The results show that an appropriate amount of Cu O can greatly promote the sintering of PMN-PZT ceramics,and at the same time,excellent piezoelectric properties can be obtained under low-temperature sintering conditions.Under the sintering condition of 950°C/2h,PMN-PZT ceramics was obtained at Cu O content of 0.3wt.%without the second phase,which with the best piezoelectric coefficient d₃₃ of 552p C/N and the maximum density.While PMN-PZT ceramics shows the maximumε_m～28000（@1k Hz,T_m）and P_r～40.4μC/cm²at Cu O content of 0.45wt.%.Cu O sintering aid can greatly reduce the sintering temperature of PMN-PZT ceramics,save energy consumption in the sintering process,and has great application potential in multi-layer piezoelectric actuators.