Institut für Materialwissenschaft, Technische Universität Darmstadt, Petersenstr. 32, D-64287 Darmstadt, Germany.
Beilstein J Nanotechnol. 2012;3:1-11. doi: 10.3762/bjnano.3.1. Epub 2012 Jan 2.
Nanoparticles of Pt-Rh were studied by means of lattice-based Monte Carlo simulations with respect to the stability of ordered D0(22)- and 40-phases as a function of particle size and composition. By thermodynamic integration in the semi-grand canonical ensemble, phase diagrams for particles with a diameter of 7.8 nm, 4.3 nm and 3.1 nm were obtained. Size-dependent trends such as the lowering of the critical ordering temperature, the broadening of the compositional stability range of the ordered phases, and the narrowing of the two-phase regions were observed and discussed in the context of complete size-dependent nanoparticle phase diagrams. In addition, an ordered surface phase emerges at low temperatures and low platinum concentration. A decrease of platinum surface segregation with increasing global platinum concentration was observed, when a second, ordered phase is formed inside the core of the particle. The order-disorder transitions were analyzed in terms of the Warren-Cowley short-range order parameters. Concentration-averaged short-range order parameters were used to remove the surface segregation bias of the conventional short-range order parameters. Using this procedure, it was shown that the short-range order in the particles at high temperatures is bulk-like.
采用基于晶格的蒙特卡罗模拟方法研究了 Pt-Rh 纳米粒子，研究内容涉及有序 D0(22)-和 40-相的稳定性如何随粒径和组成变化。通过半巨正则系综的热力学积分，得到了粒径为 7.8nm、4.3nm 和 3.1nm 的粒子的相图。观察到并讨论了尺寸依赖性趋势，例如临界有序温度降低、有序相的组成稳定性范围变宽以及两相区变窄等，这些趋势都与完整的尺寸相关纳米粒子相图有关。此外，在低温和低铂浓度下会出现有序的表面相。当在粒子的核心形成第二有序相时，观察到随着整体铂浓度的增加，铂表面偏析减少。通过 Warren-Cowley 短程有序参数分析了有序-无序转变。使用浓度平均的短程有序参数消除了传统短程有序参数的表面偏析偏差。通过该程序表明，在高温下粒子中的短程有序类似于体相。
