| Piezoelectric ceramics have become an indispensable functional ceramic for human beings in medical care,automobiles,digital communications and even public safety due to their characteristics of transforming electrical and mechanical energy.Relaxor ferroelectrics are often used as capacitors and sensors due to their low loss,high energy storage and large electrostriction.Pb(Mg1/3Nb2/3)O3（PMN）is the most typical relaxor ferroelectric,which is often used to dope and modify other ferroelectrics to improve performance,such as（1-x）Pb(Mg1/3Nb2/3)O3-x Pb Ti O3.Moreover,the piezoelectric ceramics with the best comprehensive performance are mainly lead-based ceramics.In recent years,due to the increasing awareness of global environmental protection,lead-based ceramics will volatilize lead in the process of manufacturing,production,use and disposal,which has a great impact on the environment and human health.Therefore,the development of lead-free piezoelectric ceramics has become a demand of the times.Ba(Mg1/3Nb2/3)O3（BMN）as a lead-free of relaxor,can be used to modify other piezoelectric ceramics to improve performance.In this thesis,BaTiO3 is used as the matrix,Ca2+and Ba(Mg1/3Nb2/3)O3are doped successively on the basis.The conventional solid state reaction method is used to prepare BCT-based piezoelectric ceramics with different proportions.The effects of BMN doping on the structure and properties of BCT-based lead-free piezoelectric ceramics were investigated by X-ray diffraction,Scanning electron microscope,dielectric temperature spectrum tester,hysteresis loop tester and quasi-static piezoelectric coefficient tester.Get the following results:Firstly,three sintering temperatures of 1300°C,1350°C and 1400°C are used to sinter BCTx ceramics（x=4,6,8 and 10）.The sintering temperature has an important influence on the grain growth and density improvement of ceramics,which in turn affects the dielectric and ferroelectric properties of the ceramics.The crystal grains of ceramics sintered at 1400°C are obviously enlarged,and the dielectric stability is also improved.Secondly,the sintering process at 1400°C for 3 hr was chosen to sinter the BCTx system ceramics（x=4～25）.The introduction of Ca2+can significantly inhibit the growth of crystal grains and have a significant impact on electrical properties.A proper amount of Ca2+doping can reduce the Curie temperature,improve the frequency dependence of dielectric loss,increase the remanent polarization and coercive field,and reduce the piezoelectric performance of BCTx.The 25%doping level causes Ca2+to exceed the solid solution limit,which causes defects in the microstructure and decreases in electrical properties to varying degrees.Finally,BCT20 was chosen as matrix,and introduce relaxor ferroelectric BMN into it to form a new solid solution（1-x%）Ba80%Ca20%Ti O3-x%Ba(Mg1/3Nb2/3)O3（BCT20-x%BMN）（x=0～8）.The research results show that the doping of BMN successfully introduces relaxor properties.The phase structure of ceramics gradually changes from tetragonal phase to cubic phase,which in turn causes significant changes in dielectric properties,including a decrease in Curie temperature,a substantial increase of dielectric constant at room temperature,a significant increase in frequency dispersion and a significant improve in siffusion coefficient.In addition,the ferroelectric performance has also changed significantly with the introduction of BMN.The P-E hysteresis loops at room temperature has become"slimmer",and the energy storage performance reaches its maximum value at x=6.By measuring the hysteresis loops at different temperatures,it is concluded that the introduction of BMN can improve the stability of energy storage performance.Among them,the energy storage efficiency（η%）of BCT20-6%BMN and BCT20-7%BMN in the range of20℃～150℃has little change,and the overall maintenance is above 80%,Showing the best energy storage efficiency and temperature stability. |
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