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

TL;DR

This study uncovers the chemical cage effect in liquid Li17Pb83 alloy, where lithium diffusion is confined by lead atoms due to polar covalent bonds, revealing a new mechanism for atomic transport in liquid alloys.

Contribution

It introduces the chemical cage effect as a new paradigm for understanding lithium diffusion in liquid alloys, based on electronic bonding rather than geometric constraints.

Findings

Lithium diffusion is confined within lead-formed cages.

Polar covalent Li-Pb bonds cause the cage effect.

Heterogeneous diffusion involves cage-breaking events.

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.