The Study On The Electrical And Optical Properties Of Sm³⁺ Doped CeO₂ Ion Conductor With Different Dopant Concentration

As one of the most potential electrolytes of SOFCs (Solid Oxide Fuel Cells) which are the fourth generation fuel cells, acceptor doped ceria based electrolytes have been acknowledged to be the most promising electrolytes since their simple preparation methods and higher ionic conductivities in the intermediate temperature range (500-700oC) compared with yttria stabilized zirconia (YSZ).We studied the microstructures, oxygen ionic conductivities and optical properties of samaria doped ceria solid electrolytes with different dopant concentrations in this paper. For the bulk transport properties, the oxygen vacancies concentrations, the transport enthalpy of oxygen vacancies and defect association enthalpy are dependent on the acceptor dopant concentrations. And also, acceptor-doped CeO₂ is present in the form of polycrystals, consequently, the acceptor dopant concentrations often have a significant influence on the grain boundary electrical properties. Series of solid solutions of Ce_1-xSm_xO₂-x/2 with x=0.1, 0.15 and 0.20 were synthesized by glycine-nitrate process. The effects of dopant concentrations on microstructure, the electrical properties and optical properties were investigated. The phase of Ce_1-xSm_xO₂-x/2 sintered in air at 1300oC for 10h were confirmed by X-ray diffraction to have the fluorite structure, the lattice parameter increase with increasing the dopant concentrations. The microstructures were investigated by the scanning electron microscopy (SEM), all samples exhibit a homogeneous structure, the average grain sizes are almost independent on the dopant concentrations. From the AC impedance spectroscopy, the maximum bulk conductivity was found at x=0.10, which was resulted from the smaller transport enthalpy of oxygen vacancies. The maximum grain boundary conductivity was found at x=0.20, which was resulted from the smaller space charge potential and the higher oxygen vacancies concentrations. The total electrical resistance is the sum of bulk resistance and grain boundary resistance and the electrolytes with dopant concentrations between 0.15 and 0.20 would present the best conductivity. The intensities of PL decrease with increasing the dopant concentrations, which was ascribed to the quenching effect due to the higher concentration dopping...