Preparation And Conductivity Behavior Of Doped CeO 2 - 2 O ₃ Nanocomposite Ceramics

As an excellent solid oxygen-ion conducting electrolyte, the CeO₂-based solid electrolyte has been widely applyed in the solid oxide fuel cell （SOFC）, oxygen pump, oxygen sensor, etc. It is very importang and significative to improve the ion conductivity of CeO₂ and reduce the working temperature of the solid electrolyte. Meanwhile, developing new oxide ionic conductors based on nanocomposite materials is a very effective way.In this study, the SDC2O-Al₂O₃ nanocomposite ceramics have been prepared by means of doping the transitional elements and the processes of encapulsating the grain particles. The XRD patterns of both the as-deposited and sintered at 1200℃ are consistent with the diffraction data for SDC20 phase with cubic fluorite structure and Al₂O₃. The SEM analysis indicated that the grain size of SDC2O-Al₂O₃ is in the range of 50～100 nm. The HRTEM analysis demonstrated that the experiment obtain a composite structure of SDC20 and Al₂O₃, The results of AC impedance test show that with the increase of temperature, the grain resistance （Rg） and grain boundary resistance （Rgb） all showed a trend of decrease. besides, at the same temperature, the grain boundary resistance （Rgb） is less than the grain resistance （Rg）, in addition, under the same temperature, with the increase of the Al₂O₃ content, grain boundary resistance （Rgb） gradually decreases, and when the Al₂O₃ content is to 30vol%, grain boundary resistance attain the minimum. The conductivity test results indicated that the conductivity of SDC20 encapulsated by Al₂O₃ were higher than the pure SDC20, within 5vol%-30vol% Al₂O₃, with the increase of the content of Al₂O₃, a rapid increase in conductivity of SDC2O-Al₂O₃ nanocomposite ceramics can be observed. At the same time, The ion transference numbers of the SDC2O-Al₂O₃ composite ceramics with different Al₂O₃ content in 300～650℃ were all greater than 0.94, which shows that the complex phase conductivity properties of the ceramic is almost pure ionic conductivity.In order to study the influence of the sintering temperature on the conductivity of nanocomposite ceramics SDC2O-Al₂O₃, The SDC2O-Al₂O₃ of different sintering temperature （1100℃,1200℃,1300℃） were prepared. The SEM results of nanocomposite ceramics cross section showed that with the increase of sintering temperature, the grain size increases gradually, from about 50nm to 95nm, at the same time, the density is also gradually increased with the increase of the temperature. The XRD analysis results showed that when the temperature is higher than 1200℃, a new phase SmAlO₃ was generated. The conductivity test results showed that within a certain range, with the increase of sintering temperature, the total conductivity increased, but when the sintering temperature exceeds 1200℃, the conductivity was decrease instead.In order to study the influence of the heat preservation time on the conductivity of nanocomposite ceramics SDC20-Al₂O₃, the SDC20-Al₂O₃ of different heat preservation time （1h,2h,3h） were prepared. the XRD, AC impedances and conductivity test analysis results showed that when the heat preservation time surpass 2h, which is not conducive to the improvement of electrical conductivity. The reasons may be that the heat preservation time is too long, which caused the growth of grain size and the formation of a new phase SmAlO₃, then, hindered the migration of oxygen vacancy.