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Alternative energy sources and energy storage, including all-solid-state batteries, require the search for innovative materials with promising functionalities. Systems with unusual chemical properties represent an insufficiently explored domain, concealing unexpected features. In particular, solids in eutectic systems typically undergo melting while preserving their chemical identity. Nevertheless, using diffraction and Raman spectroscopy over a wide temperature range, supported by first principles simulations, we unveil a rare phenomenon: phase-dependent chemical interactions between binary components in the NaCl-Ga2S3 system. In this unique occurrence, previously intact binary crystalline species transform upon melting into mixed liquid structural isomers, forming bonds with new partners. The chemical combinatorics, Na-Cl + Ga-S ⇄ Na-S + Ga-Cl, appears to be fully reversible for stable crystals and liquids. Despite this, rapidly frozen glasses out of thermodynamic equilibrium remain in a metastable isomeric state, offering remarkable properties, particularly a high room-temperature Na+ ion conductivity of 2.1 mS cm-1 with an activation energy of 0.249 eV, comparable to the best sodium halide superionic conductors and therefore encouraging for sodium solid-state batteries and energy applications. A rigidity paradigm is responsible for the observed phenomenon, as the extremely constrained Ga2S3 crystal lattice (with an average coordination 〈𝑟〉 = 3.2) does not survive viscous flow, breaking up at a short-range level. The removal of rigidity constraints and dense packing, approaching the optimally constrained disordered network with 〈𝑟〉 = 2.4, leads to a significant increase in empty space, as calculated using Dirichlet-Voronoi tessellation, which is the origin of high sodium diffusivity. Broadly, the rigidity-driven structural isomerism opens up an inspiring path to the discovery of atypical materials.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: all-solid-state batteries, neutron diffraction, X-ray diffraction

Date published: 2024-10-01

Publisher: Wiley

Journal:

• Small Science (ISSN: 26884046) 2400371

Funding:

• Campus France CPER ECRIN
• Foundation for Promotion of Material Science and Technology of Japan 2017A1067
• Foundation for Promotion of Material Science and Technology of Japan 2017B1771 and 2021B1197
• U.S. Department of Energy DEAC02‐06CH11357

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.4891

First published URL: https://doi.org/10.1002/smsc.202400371

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Updated at: 2024-10-25 16:30:19 +0900

Published on MDR: 2024-10-25 16:30:20 +0900