The Effect Of Al₂O₃ On The Electrical Conductivity Of SDC20/Al₂O₃ Composite Ceramics

The doped CeO₂-based solid electrolyte is an oxygen ion conductor with fluorite structure.As a conventional fuel for oxide fuel cells YSZ（yttria-stabilized zirconia）,the alternative materials have been widely studied because of its high ionic conductivity in the low and mid temperature range.In this paper,Al₂O₃ were added into 20mol%Sm-doped ceria（SDC20）to prepare SDC20/Al₂O₃ composite ceramics with nanometer scale,and the effects of Al₂O₃ addition on the electrical conductivity of SDC20/Al₂O₃ composite electrolytes were investigated.Firstly,SDC20 solid solution powder was prepared by co-precipitation method and then doped Al₂O₃ with different proportions by the means of Solid phase reaction.XRD analysis showed that there were only solid solution phases of CeO₂ with fluorite structure in the phases of SDC20 powder and SDC20/Al₂O₃ powder,and no other phases appeared.Then the powders above were sintered at 1200°C for 1h to obtain SDC20,SDC20/Al₂O₃ ceramic samples.XRD analysis showed that when the doping ratios were 0%,5%and 10%,only CeO₂ solid solution phase appeared in the SDC20/Al₂O₃ ceramic sample;when the doping ratio was 20%,not only the solid solution phase of CeO₂ but the phase of Al₂O₃ were found;however,when the doping ratios were 30%and 40%,in addition to the above two phases,the diffraction peak of the third substance SmAlO₃ appeared in the X-ray diffraction pattern,and as the Al₂O₃ increases,the intensity of the diffraction peak becomes higher.SEM analysis showed that the grain size of SDC20/Al₂O₃ ceramic samples are all within 100nm,and with the increase of doping ratio,the grain size becomes smaller and smaller.TEM and EDS test analysis showed that SDC20/Al₂O₃ composite ceramics were successfully synthesized.The relative densities of ceramic samples are all above 90%,indicating that reasonable sintering temperature and sintering time were selected in this experiment,which is suitable to the measurement of electrical conductivity of ceramic samples.The AC impedance test results show that the SDC20/Al₂O₃ ceramic sample has the highest grain conductivity and grain boundary conductivity at the same time when the doping ratio was 20%.It is consistent with the results shown by Arrhenius.All samples had ion transport numbers above 0.9.To study the influence of sintering temperature on the performance of SDC20/Al₂O₃ composite ceramics,SDC20/20%Al₂O₃ powder were sintered at1100°C,1150°C,1200°C and 1250°C for 2h,respectively,to obtain SDC20/20%Al₂O₃ composite ceramics.XRD analysis showed that,the diffraction peak of SmAlO₃ was found at 1250℃.SEM analysis showed that,with the increase of sintering temperature,the grain size becomes larger and larger,but the density of ceramic samples is also getting higher and higher.At a temperature of 1250°C,Al₂O₃with a rod-like morphology was observed.The AC impedance results show that when the temperature below 1200°C,the conductivity gradually increases as the temperature increases,reaches the maximum at 1200°C.Continuing to increase the temperature,the electrical conductivity begins to decrease drastically,and the results are consistent with the results shown by the DC.According to the analysis of Vickers microhardness analysis,the hardness increases significantly after adding Al₂O₃,indicating that the addition of Al₂O₃ can increase the mechanical strength of the material.