Modeling the Phase Stability of Janus, Core–Shell, and Alloyed Ag–Cu and Ag–Au Nanoparticles

On the basis of the Gibbs free energy (GFE) model of Janus, core–shell, and alloyed structures of Ag–Cu and Ag–Au nanoparticles, the structural stability and size-composition phase diagram are obtained. For phase segregated structure, small size and low temperature are more beneficial at fixed composition. If the temperature is fixed, the segregated phase is favored at small size and low composition. The lowest critical size to phase segregation is 6 nm for Ag–Cu NPs and 4.5 nm for Ag–Au NPs at 400 K and Ag atom fraction of approximately 50%, and raising the temperature reduces the critical size. For Ag–Cu phase diagram, it is found that the core size is dominated by the transformation between Janus and core–shell structure. When the core is sufficient large, the Ag–Cu NPs will keep the core–shell structure. As the core size gets smaller, the core location will be moved from center to off-center until it forms quasi-Janus or Janus NPs. However, for the Ag–Au phase diagram, there is no Janus structure at large scale of composition.