Preparation And Properties Of BiFeO₃-BaTiO₃ Composite Ceramics

Piezoelectric ceramics,as an important functional material which transforms electric energy and mechanical energy into each other,is widely used in electronic devices such as actuators and sensors,and plays an important role in the fields of mechanical manufacturing,military defense and so on.Pb(Zr,Ti)O₃(PZT)system ceramics are the most widely used piezoelectric ceramics at present,but with the increasing demand for environmental protection,it is urgent to find a lead-free piezoelectric ceramics which can replace PZT ceramics.BiFeO₃-BaTiO₃ lead-free piezoelectric ceramics have excellent piezoelectric properties and high temperature stability,which is considered to be the most likely to replace PZT ceramics,and thus has been widely studied.In this paper,The(1-x)BiFeO₃-xBaTiO₃ ceramics were prepared via a conventional solid state method.The oxide compounds Bi₂O₃,Fe₂O₃,BaTiO₃ and TiO₂are used as raw materials.The BiFeO₃-BaTiO₃ composite ceramics were prepared with same conditions after the powders calcined at different temperatures and time,The phase structure,microstructure,ferroelectric,dielectric and piezoelectric properties of the ceramics are studied.The results show that compared with the pure or ion doped BiFeO₃ ceramics previously studied by our research group,the impurity phase is less likely to be formed after solid solution with BaTiO₃,and the remanent polarization value Pr increases from 1?C/cm² to 26.70?C/cm²,the performance is improved significantly.The main conclusions are follows:(1)The(1-x)BiFeO₃-xBaTiO₃(x=0.25,0.30,0.35,0.40)ceramics were prepared via solid state method.XRD shows that all samples are perovskite structure with no impure phase.With the increase of x,the phase structure of ceramics gradually changed from single R phase(x=0.25)to coexistence of R phase and PC phase(x=0.30),MPB appeared,and then changed to single PC phase(x=0.35,0.40).SEM shows that the grain size almost unchanged with change x,and the maximum grain size is 6.70?m when x=0.30.The results of electrical performance test show that when x=0.30,the electrical performance is the best,which the remanent polarization P_r=26.70?C/cm²,coercive field E_C=23.25 k V/cm,and the reverse piezoelectric constant(9^*₃₃=237 pm/V,Curie temperature T_C=419?.(2)With(1-x)BiFeO₃-xBaTiO₃ as basic component,the effects of different Bicontent on properties of 0.70Bi_1+yFeO₃-0.30BaTiO₃(y=-0.02,0,0.02,0.04)ceramics were studied.The results show that when y?0,Although R phase and PC phase coexist in the sample,and MPB appeared,because Biis easy to volatilize during calcination,when Bicontent is insufficient(y=-0.02),a large amount of oxygen vacancy will be produced at high temperature to inhibit grain growth,which will affect its properties.The phase structure of the ceramics will be changed when the Biexcess(y>0),but the phase structure will be changed from MPB to single R phase,and the electrical properties of the ceramics will be reduced.Based on this,the performance of ceramics is the best when Bicontent is equal to stoichiometric ratio(y=0).(3)With(1-x)BiFeO₃-xBaTiO₃as the research object,The influence of calcination temperature on the phase structure,micromorphology and electrical properties of ceramics was studied systematically by taking 750?,800?,850?and 900?as the calcination temperature range.The crystallization property of ceramics is bad and the grain size is too small when the calcination temperature is 750?,which limits the properties of ceramics.When calcination temperature is 850?and 900?,Bivolatilization will be caused,which will cause diffraction angle shift to the right.The shrinkage of crystal cell will limit the growth of grains and affect the grain size during sintering.At 800?,the ceramic exhibits the mixture of R and PC,MPB and high density,large grain size and low leakage current,which are beneficial to the ferroelectric and piezoelectric properties of ceramics.(4)After the optimal calcination temperature is 800?,the effects of different calcination time(t=0.5 h,1.0 h,2.0 h,3.0 h)on ceramics were studied.The results show that the properties of ceramics are not different when the calcination time are t=0.5 h and t=1.0 h.When the calcination time is extended to t=2.0 h,the ceramic properties have been improved obviously,and then the calcination time is prolonged to t=3.0 h,the ceramic properties decrease slightly.This is because the calcination time of the powder is not enough when the calcination time is t<2 h.The nucleation can not be provided in the subsequent sintering process,the growth of the grains is limited,the density of the ceramics is reduced,and the ceramic properties are limited.When the calcination time is over 2 h,the calcination time is too long,which causes partial Biion volatilization,reduces the grain size and improves the leakage current density.Moreover,the phase structure changes from R phase and PC phase to single PC phase,which reduces the ceramic performance.