Physics Department, University of Genoa, Via Dodecaneso 33, 16146, Genoa, Italy.
CINaM UMR 7325, Aix-Marseille University, CNRS, Campus de Luminy, 13288, Marseille, France.
Faraday Discuss. 2023 Jan 31;242(0):52-68. doi: 10.1039/d2fd00113f.
Nanoalloys are often grown or synthesized in non-equilibrium configurations whose further evolution towards equilibrium can take place through complex pathways. In this work, we consider bimetallic systems with tendency towards intermixing, namely AgAu, PtPd and AuCu. We analyze their evolution starting from non-equilibrium initial configurations, such as phase-separated core@shell ones, by means of molecular dynamics (MD) simulations. These systems present some differences, since AuCu bulk alloys make ordered phases at low temperature whereas AgAu and PtPd remain in solid solution. Moreover, Cu, Au and Ag have similar cohesive energies whereas Pt is much more cohesive than Pd. We consider both truncated octahedral and icosahedral initial shapes in the size range between 2 and 3 nm. For each AB system, we consider both A@B and B@A core@shell starting configurations. The evolution is characterized by monitoring the time-dependent degree of intermixing and the evolution of the shape. The simulations are performed up to temperatures close to the melting range. The approach to thermodynamic equilibrium is monitored by MD simulations and compared with the equilibrium chemical configurations obtained by Monte Carlo simulations.
纳米合金通常在非平衡构型中生长或合成，其进一步向平衡态的演化可以通过复杂的途径发生。在这项工作中，我们考虑了具有混合趋势的双金属体系，即 AgAu、PtPd 和 AuCu。我们通过分子动力学（MD）模拟，从非平衡初始构型（如相分离的核壳结构）开始分析它们的演化。这些体系存在一些差异，因为 AuCu 体合金在低温下形成有序相，而 AgAu 和 PtPd 仍处于固溶体中。此外，Cu、Au 和 Ag 的内聚能相似，而 Pt 的内聚能比 Pd 高得多。我们在 2 到 3nm 的尺寸范围内考虑了截断八面体和二十面体的初始形状。对于每个 AB 体系，我们都考虑了 A@B 和 B@A 核壳的起始构型。通过监测混合程度随时间的变化和形状的演化来描述演化过程。模拟进行到接近熔化范围的温度。通过 MD 模拟监测达到热力学平衡的过程，并将其与通过蒙特卡罗模拟获得的平衡化学构型进行比较。
