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 , , 2019, , 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 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 ordered phase has been observed experimentally, the concentric multishell structure is lacking due to the difficulty of the experimental characterization.