Laser‐Generated CuPdAgPtAu High‐Entropy Alloy Nanoparticles—Thermal Segregation Threshold and Elemental Segregation

ABSTRACT In this study, noble metal HEA NPs (CuPdAgPtAu) are produced from equimolar and Cu‐ or Ag‐enriched bulk targets via laser ablation in liquids, with structural and compositional analyses by advanced electron microscopy and XRD, complemented by atomistic simulations. Equimolar targets and NPs exhibit a single fcc phase. In contrast, Cu‐ or Ag‐enriched targets show phase segregation into two fcc phases, which is not observed in the synthesized NPs. Simulations predict segregation tendencies, including Ag surface enrichment and Pt core enrichment due to surface energy differences. However, experimentally, only a Ag‐rich surface was confirmed, with the individual NPs otherwise remaining compositionally homogeneous. Thermal stability studies reveal that phase segregation can be induced post‐synthesis. Above 430°C, Cu–Ag segregation occurs, forming a second fcc phase similar to bulk targets. These findings demonstrate that rapid quenching during laser ablation suppresses thermodynamically driven segregation and kinetically stabilizes metastable solid solutions under kinetic control. Subsequent slow heating overcomes kinetic barriers, enabling equilibrium phase formation at higher temperatures. The thermal longterm stability of the Cu enriched NPs at 180°C, enrichment beyond equilibrium limits, and their tunable composition makes them promising for catalytic applications under thermocatalytic conditions while reducing noble metal usage.