Spontaneous defect formation as the origin of superionic transitions in antifluorite-type structures
- 1Department of Chemistry and Bioscience, Aalborg University, Fredrik Bajers Vej 7H, Aalborg Ø, Denmark, 9220
Abstract
Solid-state electrolytes offer the possibility of safer and higher energy density batteries, yet only a limited number of materials achieve ionic conductivities suitable for practical applications. Type-II superionic conductors, which undergo continuous temperature-driven transitions between low and high ionic conductivity regimes are strong candidates for high-performance solid state electrolytes, but the transition mechanism is not sufficiently understood. In this study, we investigate the archetypical superionic conductors Li2O and Li2S with the antifluorite structure using long-time-scale molecular dynamics simulations with an Allegro machine-learning force field (MLFF) trained on density functional theory data selected using an on-the-fly active learning procedure. To this end, superionic transitions are identified around 1450 K for Li2O and around 1100 K for Li2S through continuous peaks in the heat capacity. Diffusion coefficients and concentration of Frenkel defects are found to exhibit strong non-Arrhenius behavior coinciding with the superionic transition where both diffusion activation energy and defect formation energy decrease significantly across the transition. This suggests a self-enhanced spontaneous defect formation mechanism, which drives the superionic transition and promotes increased ionic diffusion. These results identifies the microscopic origin of type-II superionic behavior as a result of correlated defect formation and support the design of improved solid-state electrolytes.
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BibTeX
@misc{jamin2026spontaneous,
title = {{Spontaneous defect formation as the origin of superionic transitions in antifluorite-type structures}},
author = {Timothée Jamin and Kasper Tolborg},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010965/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010965/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Spontaneous defect formation as the origin of superionic transitions in antifluorite-type structures
AU - Timothée Jamin
AU - Kasper Tolborg
PY - 2026
DA - 2026/10/23
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010965/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010965/v1
AB - Solid-state electrolytes offer the possibility of safer and higher energy density batteries, yet only a limited number of materials achieve ionic conductivities suitable for practical applications. Type-II superionic conductors, which undergo continuous temperature-driven transitions between low and high ionic conductivity regimes are strong candidates for high-performance solid state electrolytes, but the transition mechanism is not sufficiently understood. In this study, we investigate the archetypical superionic conductors Li2O and Li2S with the antifluorite structure using long-time-scale molecular dynamics simulations with an Allegro machine-learning force field (MLFF) trained on density functional theory data selected using an on-the-fly active learning procedure. To this end, superionic transitions are identified around 1450 K for Li2O and around 1100 K for Li2S through continuous peaks in the heat capacity. Diffusion coefficients and concentration of Frenkel defects are found to exhibit strong non-Arrhenius behavior coinciding with the superionic transition where both diffusion activation energy and defect formation energy decrease significantly across the transition. This suggests a self-enhanced spontaneous defect formation mechanism, which drives the superionic transition and promotes increased ionic diffusion. These results identifies the microscopic origin of type-II superionic behavior as a result of correlated defect formation and support the design of improved solid-state electrolytes.
ER -