Investigation of the effect of local atomic polarization on field-enhanced ion transport in insulating binary oxides: The case of CeO2

Abstract

Over the course of more than 70 years, several theoretical models for electric field-enhanced ion diffusion in crystalline insulators have been presented. However, there is no assessment of the validity of these models despite the urge to have a correct description of field-enhanced ion diffusion in several emerging technologies. Herein, an assessment of five models was carried out by computing the field-dependent migration enthalpy $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}(E)$ for the oxide ion in ${\mathrm{CeO}}_{2}$. The input to these models is the zero-field and zero-temperature migration pathway and/or the activation barrier obtained from an interatomic potential. $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}(E)$ from these models was compared with reference values obtained from a set of classical molecular-dynamics simulations in the temperature range of $1000\phantom{\rule{4pt}{0ex}}\ensuremath{\le}T\ensuremath{\le}1600\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and the electric field range of $0\phantom{\rule{4pt}{0ex}}\ensuremath{\le}E\ensuremath{\le}30\phantom{\rule{4pt}{0ex}}\mathrm{MV}/\mathrm{cm}$. It is revealed that the most successful theoretical models are those that consider local polarization effects induced in the diffusing ion itself and its vicinity. However, all the models did not account for the effect of the electric field and finite temperature on the local polarization, leading to discrepancies between the predicted and the reference $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}(E)$, particularly at high fields. By comparing results from a rigid-ion potential and a polarizable core-shell potential, it is concluded that an intraionic polarization degree of freedom in the polarizable potential is an important factor in predicting $\mathrm{\ensuremath{\Delta}}{H}_{\mathrm{mig}}(E)$, regardless of the field-enhanced diffusion model particularly for low to moderate field. Future more accurate treatments should consider the field- and temperature-dependent interionic and intraionic local polarization effects.