EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The presence of grain boundaries in solid electrolytes has shown to reduce ionic conductivities. The resistive properties of grain boundaries can be separated into two contributions: an increased potential energy barrier at the grain boundary core as a result of the rearrangement of ions from the bulk crystal structure; and the formation of space-charge regions. Space-charge regions are areas of bulk electrolyte adjacent to the grain boundary core that possess an alter charged defect concentration as a result of the accumulation or depletion of charged defects at the core.

Mott-Schottky and Gouy-Chapman models are often employed to model space-charge regions in solid electrolytes. These one-dimensional, continuum models predict an exponential decay of charged defects away from an interface, using a simple mean-field approach to model interactions between charged species. Whilst these models perform well in the dilute limit, where a mean-field approach to defect interactions is appropriate, they have been shown to perform less well in concentrated systems.

We use kinetic Monte Carlo simulations on a model grain boundary system to test the performance of the Mott-Schottky model beyond the dilute limit. From these simulations we extract space-charge profiles for a number of concentrations and relative permittivities. We find the Mott-Schottky model performs well in a dilute regime, but defect profiles deviate from an exponential decay for concentrated systems. An analytical form is proposed for the profiles resulting from concentrated systems. We hope that this improved understanding of the behaviour of charged defects at interfaces in solid electrolytes will facilitate the generation of methods to reduce interfacial resistance in these materials.