Preparation And Doping Modification Of High-Temperature BiFeP₃-BaTiO₃ Based Lead-Free Piezoelectric Ceramics

In recent years,BiFeO3-based lead-free piezoelectric ceramics have attracted much attention due to their high Curie temperature(Tc=830 0C).The BiFeO3-BaTiO3 solid solution exhibits good piezoelectric properties and high Curie temperature(Tc=600 ?)due to the coexistence of rhombohedral(R)and pseudo-cubic(PC)phases at room temperature.However,the ceramics with effectively poled and saturated hysteresis loops are difficult to be achieved due to poorly insulating property and high dielectric loss.Therefore,it is necessary to investigate the mechanism of enhanced insulating and piezoelectric properties for achieving high-insulating and high-piezoelectric ceramics.In this paper,BiFeO3-BaTiO3 lead-free piezoelectric ceramics were prepeared by optimizing the raw materials,calcination temperature,third number doping and component content.The effect of raw materials,calcination temperature,doping and component content on the enchaned insulating and piezoelectric properites of BiFeO3-BaTiO3 lead-free piezoelectric ceramics were investigated in depth,revealing the mechanism of enchaned insulating and piezoelectric properitesThe phase structure,Bi volatilization,reaction mechanism,microstructure,and electrical properties of 0.7BiFeO3-0.3BaTiO3 ceramics prepared by solid-state reaction using BaCO3/TiO2/Bi2O3/Fe2O3(SBC)and nano-BaTiO3/Bi2O3/Fe2O3(SBT)were investigated systematically.The ceramics had different reaction paths,but showed R and PC two-phase coexistence.Compared with the conventional BaCO3/TiO2 raw materials,nano-BaTiO3 inhibited the Bi volatilization of ceramic,resulting in decreased oxygen vacancies and increased density.Compared with SBC ceramic,SBT ceramic exhibited more R phase,less Bi volatilization and Fe2+,higher density,and lower dielectric loss.Based on these,SBT ceramics obtained excellent insulation properties and ferroelectric and piezoelectric properties:Pr=3 1.2 ?C/cm2,d33=210 pC/N,Tc=514 ?,and kp=0.34.The effects of calcination temperature(760-850 ?)of nano-BaTiO3/BizO3/Fe2O3 on the phase structure,Bi volatilization behavior,microstructure,and electrical properties of 0.7BiFeO3-0.3BaTiO3 ceramics were systematically investigated.The ceramics showed R and PC phases coexistence at calcination temperature below 820 ?,and changed to PC phase at calcination temperature above 820 ?.When the calcination temperature was lower than 800? or higher than 800 ?,the Bi of ceramic would be lost in the form of Bi25FeO40 and Bi2O3,resulting in an increase in pores and a decrease in insulation property and density.Therefore,ceramics at calcination temperature of 800 ? exhibited more R phase,less Bi volatilization,fewer voids and oxygen vacancies.Based on these,the ceramics at calcination temperature of 800 ? achieved excellent insulating property and piezoelectric properties:d33=210 pC/N and kp=0.34.Due to high price of nano-BaTiO3,0.67BiFeO3-(0.33-x)BaTiO3-xBi0.5Na0.5TiO3 ceramics with excellent insulating and piezoelectric properties using BaCO3/TiO2 were prepared by traditional solid-state reaction,along with the emphasis on mechanism of ehanced insulating property.The introduction of BNT changed the main phase of the calcined powder to R and PC two-phase coexistence from R phase,but rarely affected the phase structure of the ceramics which have pure PC phase.In addition of phase structure,the introduction of BNT not only promoted the growth of grains,but also reduced the leakage current and tans.Based on the synergistic effect of increased grain size,reduced leakage current and tan8,the excellent piezoelectric properties with Pr=24.2?gC/cm2,d33=1 83 pC/N,kp=0.28 and Tc=467 ? were obtained in x=0.05 samples.In addition,the better ferroelectric and piezoelectric properties with Pr=40 ?C/cm2 and d*33(E=OV)=330pm/V were obtained at 140 ?,indicating a potential application in high temperature.In the BiFeO3-x(0.28BaTiO3-0.05Bi0.5Na0.5TiO3)system,the ceramics with 0.30?x?0.31 were R phase,while the ceramics with 0.33?x?0.34 were PC phase.These results indicate the cermic with x=0.32 was R and PC two-phase coexistence.Due to R and PC two-phase coexistence,the ceramic at x=0.32 achived excellent piezoelectric and ferroelectric properties:d33=193 pC/N and P,=29.7 C/cm2.