Another result reports an fcc-like and core/shell structure under similar experimental conditions and/or similar systems. Some experimental results had previously reported the stabilization of the Ih phase in AuCu and AuFe clusters, being this phase predominant at 25% copper concentration in both systems.
Gold and copper nanoparticles present atomic structures which are either icosahedral (Ih), decahedral (Dh) or octahedral (Oh), depending of the particle size. Finally, the optical properties of Au−Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. Besides an overall shift downward, there is a " tilting " effect on the solidus−liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). Using a regular solution model within a nanothermody-namic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. The alloy Au−Ag system is an important noble bimetallic phase, both historically (as " Electrum ") and now especially in nanotechnology, as it is applied in catalysis and nanomedicine.
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