Oxygen vacancy ordering in heavily rare-earth-doped ceria

Abstract

25 at. % Rare-earth (RE)-doped ceria samples (RE=Sm, Dy, Y, and Yb) were examined using transmission electron microscopy and electron energy loss spectroscopy, from which the oxygen vacancy ordering in nanosized domains was confirmed. The relationships of the dopant type, oxygen vacancy ordering, and ionic conductivity of doped ceria were established. It is found that the ordering of oxygen vacancies depends strongly on the dopant type, and the development of nanosized domains with a higher degree of ordering can lead to a more dramatic decrease of ionic conductivity in doped ceria.

Oxygen-vacancy ordering in lanthanide-doped ceria: Dopant-type dependence and structure model

“…Particularly, in nonstoichiometric oxides, it has been suggested that the enhancement of peak B could be introduced by the local ordering of oxygen vacancies. 17,18 For the purpose of quantitative comparison, the integral intensities of peaks B and C ͑I B and I C ͒ were calculated using an energy window of 2 eV open on the peaks ͓as illustrated in the inset of Fig. 1͑a͔͒ and the relative intensity of peak B was calculated as I B / I C .…”

“…17 In this work, the EELS study of oxygen-vacancy ordering was performed at room temperature, while the operating temperature of SOFCs based on doped ceria electrolyte, and thereby the measurement temperature for the ionic conduction in doped ceria, is around 500°C. Nevertheless, the segregation of the dopant 10,12 and the local ordering of oxygen vacancies may also exist at the measurement temperature ͑ϳ500°C͒ and have influence on the electrical conductivity because the microstructural rearrangement in doped ceria is difficult at temperatures much lower than 1000°C.…”

“…14 In addition, the "␦ phase" and the C-type oxide were also suggested in some stabilized zirconia based on the study of selected area electron diffraction ͑SAED͒. 15,16 In our previous work, 17 the local ordering of oxygen vacancies in some heavily rare-earth-doped ceria samples has been demonstrated by the study of electron energy loss spectroscopy ͑EELS͒, which could be affected by dopant type and may partly contribute to the dopant-type dependence of electrical properties of these heavily doped samples. Based on SAED patterns with ͓110͔ axis, a C-typerelated structure was suspected for the ordering.…”

“…Based on SAED patterns with ͓110͔ axis, a C-typerelated structure was suspected for the ordering. 17 However, the confirmation of this structure is required and the detailed structure model, e.g., the manner of the vacancy arrangement and of the dopant-vacancy association, is still unclear.…”

“…To detailedly characterize the oxygen-vacancy ordering, systematic studies of EELS and SAED were performed on 15 and 25 at. % Ln-doped ceria because EELS may be used to detect the oxygen-vacancy ordering in nonstoichiometric oxides [17][18][19] and SAED may provide the structural information of the ordering. Compared with the previous work, 17 clearer relationships of the oxygen-vacancy ordering, the doping level, the dopant type, and the electrical conductivity are obtained from these studies.…”