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Dense doped ceria films are promising candidate electrolytes for solid oxide fuel cells (SOFCs) operated at intermediate temperature (∼ 500 °C). In this work, detailed microstructural features of Gd-doped ceria (GDC) electrolyte film supported by Ni-GDC cermet anode were studied. Formation of inhomogeneous microstructures in the GDC film was observed, which was enhanced in the region near the film/anode interface due to the Ni diffusion from the anode. Then, the mechanism by which Ni affects the microstructure was explained by computer simulation of formation and development of defect clusters. © 2010 Elsevier B.V. All rights reserved.

Nano-sized domains have been widely observed in rare-earth-doped ceria, but their structure model remains unclear. In this work, based on the study of high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) of Gd-doped ceria, the structure model of the domains was constructed by a combination of defect clusters with oxygen vacancy chains. Then, the SAED patterns were simulated using this structure model. The simulated results are consistent with the observed SAED patterns.

Defect clusters in several rare-earth-doped ceria (doped with Y, Sm, Gd, Dy and Yb) containing up to four oxygen vacancies and eight dopant cations have been simulated and compared. In all doped ceria systems, the binding energy of the clusters increases with increasing cluster size and the oxygen vacancies tend to form curved chains in the clusters. Moreover, the capability of the growth of defect cluster is affected by dopant type, which can explain the dopant type dependency of domain development with increasing doping concentration in heavily doped ceria.

Defect clusters in Gd-doped ceria containing up to four oxygen vacancies and eight dopant cations have been simulated by the Mott–Littleton two-region approach. With increasing cluster size, the magnitude of the binding energy of the clusters increases so that the clusters become more and more stable. Moreover, the oxygen vacancies tend to form curved chains in the clusters, and the adjacent oxygen vacancies are preferentially separated by /2 in the clusters containing more than three oxygen vacancies. It is suggested that the structure of the nano-sized domains that have been reported in heavily doped ceria can be described as an aggregation and combination of these clusters.

Nano-sized domains were studied systematically in 10-30 at.% Gd-doped ceria. By using energy filtering transmission electron microscopy, it was observed that Gd cations could segregate in the domains. Due to the requirement of electrical neutrality, oxygen vacancies may also segregate into the domains with the dopant cations. Through study of electron energy loss spectroscopy, the local ordering of oxygen vacancies in the domains was further confirmed. Furthermore, the nano-sized domains and the local ordering develop with increasing doping concentration. Based on the experimental results, the formation mechanism of the domains and their effect on the ionic conductivity are discussed.