Research On Properities Of （ZrO₂）CaO Doped With Small-Content Fe,Ti,Si

10 mol%CaO stablized ZrO2 solid electrolyte(CSZ)was prepared by a chemical coprecipitation method.The influences of drying temperature,ultrasonic treatment time,calcination and sintering temperature on the grain size,dispersion of powder,and the crystal structure,microstructure,density,total ionic conductivity of solid electrolyte were studied by XRD,SEM,TG-DSC and AC impedance spectroscopy.The results showed that:(1)The powder dried at 100℃ has a good dispersion,and the aggregate particles are porous with a size range of 7～10 μm.(2)With the increase of ultrasonic time,the particle size decreases first and then increases.Powder treated by ultrasound for 15～20 min shows the best dispersion,and the aggregate powder size reduce to 0.5～1μm.(3)the crystallization of CSZ was complete at 600℃,and the phase composition is purely cubic.Calcination temperature has little effect on powder agglomeration.(4)As the sintering temperature increases,the grains grow significantly and the degree of densification increases.(5)When the sintering temperature is low(1400℃),the sample calcined at 600 showed higher total ionic conductivity;as the sintering temperature increases to 1500 and 1600℃,the calcination temperature has little influence on the total ionic conductivity.CSZ sintered at 1500℃ for 2h has the highest ionic conductivity(0.008 S·cm-1,850℃),and the activation energy is 1.24ev.CSZTx(x=0.15,0.29,1)and CSZTxSy(x=0.15,0.29,1.y=5,30)were prepared,and the influence of small-content TiO2 and SiO2 on the crystal structure,microstructure,density and total ion conductivity was studied through Archimedes method,XRD,SEM,AC impedance spectroscopy.The results are as follows:(1)CSZTx are composed of c-,tand m-ZrO2.CSZTxSy are composed of c-and m-ZrO2.There is no second phase.TiO2 promotes the transformation of c→t,and SiO2 promotes the formation of monoclinic phase.(2)The microstructures of CSZTx and CSZTxSy are polygonal grains,with the average grain size of 0.7-1.2 μm.The relative densities of samples are higher than 96%.With the increase of TiO2 content,the relative density of the sample decreases,the shrinkage rate increases,and the grain size decreases.With the increase of SiO2 content,the relative density and grain size increases firstly and then decreases.(3)The total ionic conductivities of all samples at 850℃ are above 10-3 S·cm-1,where CSZT0.15S5 is the highest(0.0042 S·cm-1),with activation energy being 0.43eV.The ionic conductivity decreases with the increase of TiO2 content,and decreases first and then increases with the increase of SiO2 content.CSZTxFy(1)(x=0,0.29.y=0,0.11,0.22)were prepared and the influence of small-amount TiO2 and FeO1.5 on the crystal structure,microstructure,density and total ionic conductivity were studied through Archimedes method,XRD,SEM,AC impedance spectroscopy.The results are as follows:(1)CSZTxFy is composed of cubic phase and monocline phase ZrO2,and no second phase generated.All diffraction peaks slightly shifte to the right.(2)The relative densities of all samples are higher than 96%,and the average grain size is 0.79～1.02 μm.FeO1.5 promotes sintering process and increases relative density,but has little effect on grain size.(3)The ionic conductivities at 850℃of all sample are greater than 10-2 S·cm-1,and the activation energy is 0.449～0.488eV.The total ionic conductivity increases as the FeO1.5 content increases.CSZT0.29F0.22 shows the highest total ionic conductivity(0.017 S·cm-1,0.483 eV).CSZTxFy(Ⅱ)(x=0,0.29.y=0,0.11,0.22)were prepared by changing the deposition rate to study the conduction process of grain boundary.The crystal structure,microstructure,relative density and grain boundary,total ionic and electronic conductivities were analyzed by Archimedes method,XRD,SEM,AC impedance spectroscopy and Hebb-Wagner method.The results are as follows:(1)Compared with groupⅠ,the phase composition is the same being cubic phase and monoclonal phase,and the grain size significantly increases,ranging from 15.31 to 21.83 μm,and the relative densities are higher than 96%.The total ionic conductivities are slightly lower than those of group Ⅰ,being 0.005～0.009 S·cm-1,and the activation energy is 1.179～1.199eV.(2)As the temperature increases,the grain boundary resistance decreases rapidly and begins to disappear at 800℃.The total ionic conductivity depends on the bulk resistance at low temperature(<750 ℃)and grain boundary resistance at high temperature(>750 ℃).(3)The grain boundary conductivity decreases with FeO1.5 or TiO2 doping singlely,but increases with FeO1.5 and TiO2 co-doping.(4)The blocking coefficient of CSZT0.29F0.22 is the lowest being 0.026;(5)TiO2 can move SiO2 at the grain boundary to the triple-phase interface and reduce the grain boundary resistance.However,this process needs sintering aids such as FeO1.5 to catalyze.(6)The electronic conductivity increases as the doping content increases,and the electronic conductivity of all samples was 10-8～10-7 S·cm-1.According to the experimental results of the full paper,we can conclude that:(1)Ultrasonic-precipitation method can effectively improve the agglomeration phenomenon of powders and obtain powder with good dispersibility.(2)The type,content and solid solubility of dopant have an important influence on the ionic conductivity.(3)Compared with the Si-Ti codoping,the grain size and relative density of Fe-Ti codoping were similar.However,CSZ doped with Fe and Ti has a higher total ionic conductivity(10-2 S·cm-1,850℃)and low electronic conductivity,which is a kind of excellent solid electrolyte.