Probing Anharmonic and Heterogeneous Carrier Dynamics Across Sublattice Melting in a Minimal Model Superionic Conductor

TL;DR

This study introduces a minimal model to understand sublattice melting and ion transport in superionic conductors, revealing how lattice softness and anharmonicity influence ion dynamics and enabling control over the melting process.

Contribution

The paper presents a minimal binary model capturing sublattice melting and ion dynamics, linking lattice properties to transport behavior in superionic conductors.

Findings

Identification of three dynamical regimes: crystalline, sublattice-melt, and fully molten.

Near sublattice melting, carrier motion is strongly anharmonic and heterogeneous.

Sublattice melting can be tuned by adjusting carrier density, affecting ion transport.

Abstract

Despite decades of research, the microscopic origin of sublattice melting and fast ion transport in superionic conductors remains elusive. Here, we introduce a chemically neutral minimal binary model consisting of a rigid host lattice stabilized by short-range steric repulsion and a soft carrier sublattice interacting via long-range Wigner-type forces. This contrast naturally produces distinct melting temperatures and an intermediate sublattice-melting phase in which carriers become fluidlike while the host remains crystalline. Molecular-dynamics simulations identify three dynamical regimes-crystalline, sublattice-melt, and fully molten-marked by sharp changes in diffusivity, structural correlations, and dynamic heterogeneity. Near sublattice melting, carrier motion is strongly anharmonic and spatially heterogeneous, beyond mean-field hopping descriptions. By tuning the density, we demonstrate that sublattice melting can be continuously controlled, establishing a direct link between lattice softness, anharmonicity, and collective ion transport. This work provides a unified microscopic foundation for designing mechanically robust, high-performance superionic conductors operable near ambient conditions.