Structure And Properties Of BiFeO₃-BaTiO₃ Lead-free Piezoelectric Ceramics Via Oxide Sintering Aids

BiFeO₃-BaTiO₃（BFO-BTO）has attracted much attention due to its high Curie temperature and piezoelectric activity,as well as the morphotropic phase boundary structure with the coexistence of rhombohedral phase and pseudocubic phase,where good dielectric,piezoelectric and ferroelectric properties are achieved.However,Bi element in the main crystalline phase of BiFeO₃ is volatile in the sintering process at high temperature,and Fe³⁺is easy to change valence to Fe²⁺,which brings about a high leakage current in BFO-BTO,and it is difficult to fully polarize BFO-BTO material under high temperature and high voltage,and its electrical properties are limited.In this paper,the traditional solid-state reaction method was used to prepare 0.7BiFeO₃-0.3BaTiO₃ ceramics,and the effect of oxide sintering aid Sb₂O₃,SiO₂ and CuO on the sintering,structure and electrical properties of BFO-BTO piezoelectric ceramics was studied,in order to reduce the sintering temperature,improve the insulation performance and piezoelectric properties.The main contents are as follows:Firstly,the effect of Sb₂O₃ doping on the structure and electrical properties of BFO-BTO ceramics was investigated,and the modification mechanism was discussed.Sb₂O₃ doping enhances sintering and grain growth,increases ferroelectric relaxation,and decreases Curie temperature T_c.Sb doping causes lattice distortion of BFO-BTO ceramics,which promotes the transformation of BFO-BTO from normal ferroelectric to relaxor ferroelectric.Conductive characteristics and XPS test results indicate that oxygen vacancy is the main carrier.Sb doping does not change the conductive mechanism of the ceramics,but reduces the oxygen vacancy and Fe²⁺concentration,thus reducing the electrical conductivity and high temperature loss,and improving the insulation.When adding 0.05 wt%Sb₂O₃,good electrical properties of the ceramics are acheived:T_c≈520℃,d₃₃=213 pC/N,k_p=28.8%.Secondly,the effect of SiO₂ doping on the structure and electrical properties of BFO-BTO ceramics was investigated.SiO₂ doping can reduce the sintering temperature,reduce the loss and improve the insulation of ceramics.SiO₂ induces the BFO-BTO ceramics to transform from pseudo-cubic phase to rhombohedral phase with more uniform grain.SiO₂ can markedly increase the relaxation of BFO-BTO ceramics,close to the ideal relaxation ferroelectric,while Curie temperature still maintain a high value（T_c≥520℃）.In general,SiO₂ shows the characteristics by“hard”doping.When the doping amount of SiO₂ is x=0.05,d₃₃=197 pC/N,k_p=0.34,T_d≥400℃.Finally,on the basis of SiO₂ doping,the effect of CuO doping on the structure and electrical properties of BFO-BTO-Si+xCuO ceramics was discussed.CuO doping strengthened the rhombohedral phase structure of BFO-BTO-Si ceramics,enhanced the ferroelectric properties,and significantly increased the Curie temperature.The addition of 0.075 wt%CuO increased the T_c of BFO-BTO-Si ceramics from～500℃to～550℃.Cu and Si co-doping significantly improves the piezoelectric properties of ceramics and widens the sintering range,thus obtaining piezoelectric ceramics with high Curie temperature,piezoelectric properties and good temperature stability.When x=0.10,the ceramics achieved the optimum electrical properties:d₃₃=234 pC/N,k_p=0.37,Q_m=32,T_c≈545℃,T_d≈480℃,tanδ=0.052,E_c=26.15 k V/cm,P_r=25.1μC/cm².