Local Symmetry Breaking Induced Superionic Conductivity in Argyrodites

Argyrodites have complex crystal structures that give rise to extraordinary physical properties, including ultralow thermal conductivity and superior ionic conductivity, which have received wide interest in thermoelectric materials and rechargeable batteries. While the long-range crystallographic structures of argyrodites have been well characterized, the local atomic-scale structural features remain poorly understood. In this work, synchrotron X-ray atomic pair distribution function (PDF) analysis has been carried out to investigate the short-range structural correlations in Ag₈GeS₆ argyrodites and their structure evolution with temperature. Strikingly, the local atomic arrangement shares similarity across the superionic phase transition, and the phenomenon is further validated in other Ag-based argyrodites. Our analysis reveals that the local structural distortion, weak bonding environment, and strong lattice anharmonicity could be the key to understanding the exotic thermal and ion transport behavior. This work explores the critical connection between local structural motifs and macroscopic functionalities in Ag-based argyrodites, proposing a new local-structure-oriented strategy for designing next-generation functional materials.