Structural stability of alloyed and core–shell Cu–Pt bimetallic nanoparticles

Combining the bond-energy model and Debye theory, we generalized the Gibbs free energy model for Cu–Pt nanoparticles (NPs) by introducing a shape factor considering the shape effect. We studied the structural stability of the Cu–Pt NPs and plotted the corresponding composition-, shape- and size-dependent phase diagrams. It is shown that the Cu–Pt NPs can form alloyed structure in a large size range. But when the particle size continues to decrease, the NPs will form the core–shell structure due to surface segregation. Meanwhile, the composition segregation could make the atoms of less-content element to gather in the surface. The predictions from the present calculated phase diagrams are consistent with a series of experimental results in literatures. To further prove the efficiency of the phase diagrams, we synthesized the alloyed Cu–Pt NPs of 4–15 nm by a co-reduction method, which is in agreement with the predictions from the phase diagrams.