Effects of dopant ions on the conductivity of Ce0.75Sm0.2M0.05O1.875 (M = Al, Fe, Y, Bi) electrolytes.

In this paper, the relationship between the phase purity, microstructure, conductivity and thermal expansion of the M (Al, Fe, Y and Bi) doped SDC (Ce_0.8Sm_0.2O_1.9) electrolytes was investigated. Ce_0.75Sm_0.2M_0.05O_1.875 (M = Al, Fe, Y, Bi) electrolytes were prepared by sol-gel auto-combustion process. From XRD analysis, the dopant ions (Al, Fe, Y and Bi) are doped in the lattice of cubic fluorite structure of SDC and no second phase is formed for Ce_0.75Sm_0.2M_0.05O_1.875 (M = Al, Fe, Y, Bi) calcined at 700 °C for 4 h. However, the impurity phase of Ce₂O₃ is formed for Ce_0.75Sm_0.2Al_0.05O_1.875 sintered at 1400 °C for 4 h. Moreover, the relative densities of the samples increase after doped with Fe, Y and Bi. While Al doping cannot improve the sintering performance and decreases the density. These results are consistent with the SEM images. In addition, the grain size of Ce_0.75Sm_0.2Bi_0.05O_1.875 is the largest as indicated by SEM microstructure. More importantly, the average thermal expansion coefficient and ionic conductivity of the sintered samples improves after doped with Fe, Y and Bi, which suggests that Ce_0.75Sm_0.2M_0.05O_1.875 (M = Al, Fe, Y, Bi) can be a potential electrolyte for the IT-SOFC. [ABSTRACT FROM AUTHOR]