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 CeO₂. Simulation cells containing oxygen vacancies were subjected at temperatures 1000≤T/K≤1600 to electric field strengths 0.1≤E/MVcm^-1≤40 to obtain the oxygen-ion mobility uᵢ(E,T). In addition, static nudged-elastic-band calculations were performed to obtain directly the forward/reverse barriers for oxygen-ion migration, ΔHmigf/r. Qualitatively, uᵢ 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 ΔHmigᶠ at high E and thus overestimates uᵢ. A new, superior analytical expression for uᵢ(E,T) is consequently derived.