Phase Separation Prior to Alloying Observed in Vacuum Heating of Hybrid Au/Cu₂O Core–Shell Nanoparticles

The coexistence of decomposition, phase segregation, and alloying behaviors of Au@Cu2O core–shell nanoparticles were found through in situ heating transmission electron microscopy imaging and spectral-analysis techniques. Thermally induced compositional variations (from Cu2O to Cu) were observed to be present in the nanoparticle shells, which was followed by a spontaneous occurrence of Au–Cu alloying. The higher-Cu loading (1:10 Au/Cu) sample displays a clear Cu/Cu2O phase segregation driven by the internal stresses resulting from lattice mismatch. Cu extrusions also occur in this sample after storage in ethanol for 10 days. These in situ observations/findings may help enhance a fundamental understanding of remarkable experimental aspects arising in catalytic processes and other applications as well as provide a valuable reference for testing/refining potential models of hybrid nanoparticles in theoretical calculations.