Insights on oxide ion transport in yttria-doped ceria from molecular dynamics simulations

Yttria-doped ceria (YDC) is one of the most promising solid electrolytes for solid oxide fuel cells (SOFC) operating at intermediate temperatures (500–750∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C) owing to its high oxygen ion conductivity, among other favorable properties. Employing classical molecular dynamics (MD) technique, yttria-doped ceria,YxCe1-xO2-x/2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Y}_{x}\text{Ce}_{1-x}\text{O}_{2-x/2}$$\end{document}, is investigated over the dopant concentrations, x =4 to 40 mol% at 1300 K. The gross structural and dynamical features of the system, such as the variation of lattice parameters and ionic conductivity, from the present study are in good agreement with previous experimental and theoretical reports. The oxygen ion conductivity shows a pronounced maximum around x= 14 mol% of yttrium doping and drops off thereafter. The observed variation in the ionic conductivity is found to be associated with a non-monotonic variation of the residence time of the oxygen ions at their tetrahedral locations in the fluorite lattice. It is noted that the energy of oxygen ions increases systematically with the number of yttrium in their local environment. Further, the microscopic energy barrier for ion hops along the various channels connecting the distinct oxygen environments is also sensitive to the yttrium presence. The statistically averaged barriers along these channels produce a minimum for the high conducting composition, thereby explaining the observed conductivity variation.