Low Temperature Sintering And Doping Modification Of（Ba,Ca）（Ti,Sn）O₃Lead-free Piezoelectric Ceramics

BaTiO3-based lead-free piezoelectric ceramics attract much attention in recent years due to their increased piezoelectric properties.(Ba,Ca)(Ti,Sn)03piezoelectric ceramics with two or more phases at room temperature show excellent piezoelectric properties (d33>400pC/N), but they must be sintered over1450℃to achieve densification, which impedes their practical application to some extent. It is necessary to lower the sintering temperature of high-performance (Ba,Ca)(Ti,Sn)O3piezoelectric ceramics. In this study, Li2CO3, Li2O, CuO, CuO-B2O3doped (Ba0.95Ca0.05)(Ti0.90Sn0.10)03(BCTS) and CuO doped Ba(Tio.9oSno.10)03(BTS) ceramics were prepared by traditional solid state sintering. The effects of sintering aids and sintering temperature (Ts) on the phase structure and electrical properties for BCTS and BTS ceramics were investigated.The dense sintering temperature of BCTS ceramics was reduced to1300℃with adding Li2CO3over2mol%. All BCTSLi2x ceramics have coexisting R and T phases at room temperature, whose specific ratio of R to T phase decreases with increasing Li2CO3. Due to the increased grain size and density as well as the variation in the specific ratio of R to T phase, BCTSLi6ceramic shows better piezoelectric properties of d33=485pC/N and kp=39%.Dense BCTS ceramics were also obtained at1300℃by adding2mol%or more Li2O. All BCTSLix ceramics have coexisting R and T phases at room temperature, along with a decreased specific ratio of R to T phase with increasing Li2O. As increasing Ts from1300℃to1450℃, oxygen vacancy generated by the substitution of Li+for Ti4+or Sn4+decreases and that leaded by the inadequate oxygen supply in environment increases, and the concentrations of oxygen vacancy first decreases and then increases in BCTSLi4ceramics. All BCTSLi4ceramics at room temperature have coexisting R and T phases whose specific ratio changes with increasing Ts. Optimized piezoelectric properties of d33=578pC/N and kp=39%were obtained as as=1350℃, which is attributed to the appropriate specific ratio of R to T phase.The dense sintering temperature of BCTS ceramics was reduced to1150℃as adding2mol%CuO. BCTSCu2ceramics are R-T phase coexistence as sintered at1150-1200℃and R-T-PC phase coexistence as sintered at1250-1450℃. Due to coexisting R, T and PC phases with appropriate specific ratio, BCTSCu2ceramics sintered at1300℃show excellent piezoelectric properties of d33=735pC/N and kp=57%.Adding0.5mol%CuO reduced the densification sintering temperature of BCTS to1200℃. With the increasing of B2O3, B3+enters initially tetrahedral sites and then the sites between an apical O2-and Ti4+and oxygen vacancy. Due to proper proportion of R and T phase, BCTSCu0.5B1.4ceramics show better piezoelectric properties with d33=360pC/N and kp=30%.The addition of1mol%CuO lowered the sintering temperature of BTS to1200℃. BTSCui samples shows coexisting R and T phases with d33=250-360pC/N as Ts=1200-1300℃and R, T and PC phases with d33=500-650pC/N as Ts=1350-1550℃at room temperature. Owing to the coexistence of R, T and PC phases with appropriate component ratio at room temperature, BTSCu1ceramic sintered at1450℃shows excellent piezoelectric properties with d33=650pC/N and kp=52%, which is increased by110%compared with BTS ceramics.BTSCu1and BCTSCu2ceramics show excellent piezoelectric properties with d33=650pC/N and735pC/N at room temperature, which is comparable to that of PZT-5H ceramics. BCTSCu2ceramic with high piezoelectric properties and low sintering temperature is one of the good lead-free candidates to replace the lead-based piezoelectric ceramics.