Microstructural and chemical aspects of working-temperature aged Ca-doped CeO2

Aging behavior investigation can provide a necessary basis for evaluating the suitability of doped ceria as the electrolyte material for intermediate temperature solid oxide fuel cells under working circumstances. In the current study, the microstructural and chemical variations of Ca-doped CeO2 with various aging conditions have been systematically investigated by means of transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), X-ray photoemission spectroscopy (XPS) and X-ray diffractometry (XRD). TEM shows that crystal defects in terms of microdomain and superstructure are alleviated by the aging processing. Reduction of the tetravalent Ce can be induced by high temperature aging, and the reduction fraction has been quantitatively determined within a broad temperature range. A new cerium oxide phase with a crystal structure of primitive monoclinic (a = 1.31 ± 0.013 nm, b = 0.38 ± 0.004 nm, c = 3.52 ± 0.035 nm, and β = 94.7 ± 0.3°) has been determined in the high temperature aged specimens. The possible effects of the evolutions in the microstructure and material chemistry on the ionic conductivity are discussed.