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

Abstract

Studies of electron energy loss spectroscopy and selected area electron diffraction (SAED) were systematically performed on 15 and $25\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$ lanthanide (Ln)-doped ceria samples ($\mathrm{Ln}=\mathrm{Sm}$, 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 $(\mathrm{Gd},\mathrm{Sm})>\mathrm{Dy}>\mathrm{Yb}$. Furthermore, a monotone correlation between the development of the ordering and the degradation of ionic conductivity with increasing the doping concentration from 15 to $25\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$ 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 ${\mathrm{Ln}}_{2}{\mathrm{O}}_{3}$ oxides and the $\frac{1}{2}⟨110⟩$ pairs of the vacancies are preferred. Then, the factors that can influence the formation of the ordering are discussed.