Overscreening and Underscreening in Solid-Electrolyte Grain Boundary Space-Charge Layers

TL;DR

This paper demonstrates that non-dilute solid electrolyte grain boundaries exhibit overscreening and underscreening phenomena similar to those in liquid electrolytes, using Monte Carlo simulations to reveal complex space-charge behaviors.

Contribution

It introduces the first detailed simulation study showing overscreening and underscreening in solid electrolyte grain boundaries beyond the dilute limit.

Findings

Overscreening causes damped oscillatory charge profiles.

Underscreening results in decay lengths longer than Debye length.

Behavior parallels phenomena in concentrated liquid electrolytes.

Abstract

Polycrystalline solids can exhibit material properties that differ significantly from those of equivalent single-crystal samples, in part, because of a spontaneous redistribution of mobile point defects into so-called space-charge regions adjacent to grain boundaries. The general analytical form of these space-charge regions is known only in the dilute limit, where defect-defect correlations can be neglected. Using kinetic Monte Carlo simulations of a three-dimensional Coulomb lattice gas, we show that grain-boundary space-charge regions in non-dilute solid electrolytes exhibit overscreening -- damped oscillatory space-charge profiles -- and underscreening -- decay lengths that are longer than the corresponding Debye length and that increase with increasing defect-defect interaction strength. Overscreening and underscreening are known phenomena in concentrated liquid electrolytes, and the observation of functionally analogous behaviour in solid electrolyte space-charge regions suggests that the same underlying physics drives behaviour in both classes of systems. We therefore expect theoretical approaches developed to study non-dilute liquid electrolytes to be equally applicable to future studies of solid electrolytes.