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 MonteCarlo simulations of a three-dimensional Coulomb lattice gas, we show that grain boundary space-charge regions in nondilute 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 behavior in solid electrolyte space-charge regions suggests that the same underlying physics drives behavior in both classes of systems. We therefore expect theoretical approaches developed to study nondilute liquid electrolytes to be equally applicable to future studies of solid electrolytes.
Highlights
Using kinetic Monte Carlo simulations of a three-dimensional Coulomb lattice gas, we show that grain boundary spacecharge regions in nondilute 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
Weakly coupled systems, we recover the behavior predicted by classic treatments of space-charge behavior, i.e., the linearized Poisson-Boltzmann model—the space-charge profile decays exponentially to the asymptotic bulk value with a decay length equal to the Debye length λD
Strongly coupled systems, we observe damped oscillatory space-charge profiles—overscreening—and space-charge decay lengths that are larger than the corresponding Debye length— underscreening
Summary
Using kinetic Monte Carlo simulations of a three-dimensional Coulomb lattice gas, we show that grain boundary spacecharge regions in nondilute 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. We find that in nondilute solid electrolytes (high defect concentrations) or for strong defect-defect interactions (low relative permittivities) grain-boundary–adjacent spacecharge profiles have a qualitatively different functional form to the monotonic decay predicted by classic spacecharge theory.
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