Atomistic Mechanisms Underlying Non-Arrhenius Ion Transport in Superionic Conductor AgCrSe₂

Superionic conductors have promising applications in energy harvesting and storage. The atomistic mechanisms underlying non-Arrhenius ion transport exhibited by a subclass of these materials, however, remain poorly understood. Here, we use molecular dynamics simulations based on a classical force field to study the long-time diffusional dynamics of Ag⁺ions in AgCrSe₂. The simulations provide quantitative predictions of the order-disorder transition and ionic conductivity across a wide range of temperatures. The simulations also provide insights into ion transport, specifically revealing how non-Arrhenius transport arises from repulsion between ions occupying adjacent sublattice sites, how spatiotemporal correlations lead to distinct ion migration patterns at low versus high temperatures, and how lattice flexibility enhances transport rates by lowering energy barriers along the migration path and mitigating ion-ion repulsion. The transport mechanisms revealed here and the modified activated-transport model of ion diffusion proposed here should be relevant to a broad range of superionic materials.