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 u(i)(E, T). In addition, static nudged-elastic-band calculations were performed to obtain directly the forward/reverse barriers for oxygen-ion migration, Delta H-mig(f/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 Delta H-mig(f) at high E and thus overestimates ui. A new, superior analytical expression for u(i)(E, T) is consequently derived.