Composition-dependent chemical ordering predicted in Pt-Ag nanoalloys.

Pt-Ag nanoalloys display an astonishing chemical organization depending on their size and composition. Reversed size-dependent stabilization of ordered nanophases [J. Pirart et al. , Nat. Commun. , 2019, 10 , 1982-1989] has recently been shown around equiconcentration. We extend this study by a theoretical investigation on the whole range of compositions showing a significant composition-dependent chemical ordering in Pt-Ag nanoalloys. At a low silver content, the surface exhibits a strong Ag segregation coupled to a (2 × 1) superstructure on the (100) facets. By increasing the silver concentration, the system displays an L1 1 ordered phase in the core, interrupted in a narrow range of concentrations by a concentric multishell structure characterized by an alternation of Ag-pure/Pt-pure concentric layers starting from the surface shell to the core. Although the L1 1 ordered phase has been observed experimentally, the concentric multishell structure is lacking due to the difficulty of the experimental characterization.