Field-enhanced ion transport in solids: Reexamination with molecular dynamics simulations

Classical molecular-dynamics simulations were used to examine the effect of an electric field on the mobility of oxygen ions in the model crystalline oxide ${\mathrm{CeO}}_{2}$. Simulation cells containing oxygen vacancies were subjected at temperatures $1000\ensuremath{\le}T/\mathrm{K}\ensuremath{\le}1600$ to electric field strengths $0.1\ensuremath{\le}E/\mathrm{MV}{\mathrm{cm}}^{\ensuremath{-}1}\ensuremath{\le}40$ to obtain the oxygen-ion mobility ${u}_{\mathrm{i}}(E,T)$. In addition, static nudged-elastic-band calculations were performed to obtain directly the forward/reverse barriers for oxygen-ion migration, $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}^{\mathrm{f}/\mathrm{r}}$. Qualitatively, ${u}_{\mathrm{i}}$ behaves as expected: independent of $E$ at low values of $E$ and exponentially dependent on $E$ at high values. The quantitative (standard) Mott-Gurney treatment, however, underestimates $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}^{\mathrm{f}}$ at high $E$ and thus overestimates ${u}_{\mathrm{i}}$. A new, superior analytical expression for ${u}_{\mathrm{i}}(E,T)$ is consequently derived.