Addition Of Bi_0.75Y_0.25O_1.5 To Ce_0.8Y_0.2O< Sub>1.9The Effect Of Ceramic Sintering And Electrical Conductivity

CeO₂-based electrolyte has been regarded as a superior oxygen ion conducting ceramic,whereas the poor sintering properties,lower ion conductivity,and inferior physicochemical stability severely limit their extensively application.It has been demonstrated that doped Bi₂O₃ has high ionic conductivity and low melting point.The introduction of doped Bi₂O₃ in the doped CeO₂ can increase the relative density,lower the sintering temperature and improve the grain boundary electrical conductivity of the sample.Therefore,the Y-stable Bi₂O₃(Bi_0.75Y_0.25O_1.5,YSB)as sintering aids was adopted to enhance the ionic conductivity and sintering properties of Y-doped CeO2(Ce0.8Y0.2O1.9,YDC).In this study,Ce_0.8Y_0.2O_1.9(YDC)and Bi_0.75Y_0.25O_1.5(YSB)powders were prepared by sol-gel method and co-precipitation method,respectively.YDC-x YSB composite ceramics were harvested by mixing the above powders in given weight ratio,axially pressing,and then sintering at 1100^°C for 6 h.XRD results showed that YDC-x YSB(x=0,5,10,20,30,40 wt%)dense pellets only consist of YDC and YSB phases.Compared to the pure YDC,the sintering temperature of composite ceramics with5wt%YSB addition can be decreased by 250^°C?300^°C,whereas when the amount of YSB addition greater than 5 wt%,the relative density of composite ceramics gradually decreases due to the raised YSB volatilization.SEM results revealed that the average grain size decrease from 210.5 nm to 85.7 nm when the addition of YSB from 5 wt%to 40 wt%,indicating YSB can inhibit the growth of YDC grain during the sintering process at 1100^°C.TEM analysis displayed that YSB is mainly located in grain boundaries.AC impedance indicated that the total conductivity of YDC-x YSB(x>5wt%)is lower than that of YDC during 200^°C?500^°C,while it gradually exceeds that of YDC during 500^°C?750^°C.At 750^°C,the superior total conductivity value of YDC-30%YSB(6.22×10^-2 S/cm)is about 1.35 times that of YDC.In order to investigate the effect of sintering temperature on the ion conductivity of YDC-x YSB,YDC-30%YSB composite ceramics was sintered from 900^°C to1300^°C.XRD results implied that YDC-30%YSB pellets sintered from 900^°C to1200^°C only contain cubic fluorite phase.However,the impurity phases are generated in the sample when the sintering temperature reach to 1300^°C.The density test suggested that the relative density of YDC-30%YSB is lower than that of YDC when the sintering temperature is less than 1100^°C,while its relative density decrease when the sintering temperature is higher than 1100^°C.Such results can be attributed to the elevated YSB volatilization.On the other hand,as for YDC-30%YSB(900^°C),YSB phase with the shape of flakes is scattered between the crystal grains,generating a fluffy microscopic morphology.Meanwhile,YDC-30%YSB sample sintered at 900^°C and1000^°C have a large number of pores and low crystallinity.However,when the sintering temperature is 1300^°C,YSB can promote the growth of YDC grains.AC impedance test showed that the total conductivity of each YDC-30%YSB sample measured during200^°C?400^°C is lower than that of YDC.When the test temperature rises up to 750^°C,the total conductivity of YDC-30%YSB sintered at 1100^°C exceeds that of YDC and reaches the maximum value(6.22×10^-2 S/cm),while the total conductivity of YDC-30%YSB sintered at 1200^°C and 1300^°C is still lower than that of YDC.To further examine the effect of the addition amount of YSB on the performance of YDC,YDC-x YSB(x=0,0.5,2,4,8 wt%)ceramics were sintered from1100^°C?1300^°C.The XRD results implied that both YDC-x YSB samples sintered at1100^°C or 1300^°C only contain cubic fluorite phase.The density measurement results showed that the relative density of YDC-x YSB(x?4 wt%)sintered at 1100^°C is lower than that of YDC because the YSB phase inhibits the grain boundary migration during the sintered process.The relative density of YDC-YSB achieved the maximum value(99%)when the amount of YSB is 2 wt%.The grain conductivity of YDC-x YSB sintered at 1300^°C reached the maximum value(400^°C,9.98×10^-4 S/cm)when the addition of YSB is 0.5 wt%,which is about 1.31 times higher than that of YDC.However,the further increase of YSB(0.5 wt%<x<8 wt%)will lead to the decrease of grain conductivity.Moreover,owing to the YSB can be regarded as a fast ion channel above 300^°C,the grain boundary conductivity of composite ceramic will be improved with the increase of YSB content at 400^°C.In this respect,the maximum grain boundary conductivity of YDC-8%YSB(4.56×10^-3 S/cm at 400^°C)is about 3.28 times than that of YDC.