Mobile chemical cage: Revealing the origin of anomalous lithium diffusion in liquid $Li_{17}Pb_{83}$ alloy

Abstract

The high-temperature performance of liquid $Li_{17}Pb_{83}$, a key fusion reactor material, is governed by its atomic-scale dynamics. Using ab initio molecular dynamics, we discover that lithium diffusion is not free but confined within cages formed by lead atoms, a phenomenon we term the chemical cage effect. Structurally, RDF and CSRO analyses confirm a stable local environment where Li is preferentially surrounded by Pb. Dynamically, the MSD and NGP reveal anomalous, heterogeneous lithium diffusion characterized by repeated cage-breaking events. The double-exponential relaxation of the Li-Pb bond probability further distinguishes the escape dynamics of Li from surface and bulk cages. ELF and DOS analyses identify the polar covalent Li-Pb bond as the electronic origin of this cage. This study establishes the chemical bond-directed synergistic cage effect as the core mechanism in $Li_{17}Pb_{83}$, moving beyond traditional geometric constraint models and providing a new paradigm to understand transport in multi-component liquid alloys.