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

Studies of electron energy loss spectroscopy and selected area electron diffraction (SAED) were systematically performed on 15 and 250.3em0exat.0.2em0ex% lanthanide (Ln)-doped ceria samples (Ln=Sm, Gd, Dy, and Yb), through which the local ordering of oxygen vacancies that develops with increase in doping level was confirmed in the sequence of (Gd,Sm)>Dy>Yb. Furthermore, a monotone correlation between the development of the ordering and the degradation of ionic conductivity with increasing the doping concentration from 15 to 250.3em0exat.0.2em0ex% was observed. Based on the analysis of SAED patterns, a structural model for the ordering of oxygen vacancies has been constructed, in which the arrangement of oxygen vacancies is similar to that in C-type Ln₂O₃ oxides and the 1/2⟨110⟩ pairs of the vacancies are preferred. Then, the factors that can influence the formation of the ordering are discussed.