Phase Behavior of Rb-Na Liquid Metal Alloys: An Ab Initio-Based Molecular Dynamics Perspective

Liquid alloys of alkali metals have attracted considerable interest for their potential use in cooling systems and batteries, driven by the need for environmental protection and technological advancement. This research thoroughly explores the factors influencing the phase diagram of RbxNa1-x. We have qualitatively reproduced the experimental results using the thermodynamic integration method and machine learning interatomic potentials based on ab initio molecular dynamics simulations. We uncovered the subtle interplay between the energy and entropy factors that affect phase stability. Further analysis reveals the significant roles of volume and atomic mass on the phase diagram. Moreover, the atoms display unique clustering behaviors: Na atoms typically avoid one another, whereas Rb atoms tend to cluster together, likely due to ionization energy differences. In addition, the diffusion behavior also varies; Rb diffuses more at higher concentrations, whereas Na diffuses more at lower concentrations. These findings provide valuable insights into the phase stability and the dynamic and structural properties of these complex liquid metal alloys.