Taranovskyy Andriy, Tomán János J, Gajdics Bence D, Erdélyi Zoltán
Department of Solid State Physics, Faculty of Science and Technology, University of Debrecen, PO Box 400, H-4002, Debrecen, Hungary.
Phys Chem Chem Phys. 2021 Mar 18;23(10):6116-6127. doi: 10.1039/d0cp06695h.
Determining binary phase diagrams for nanoparticles proves to be a very difficult task regardless if it is tried either by computer simulations, theoretical considerations or experiments. In this work, using 3D Object Stochastic Kinetic Modelling Framework (3DO-SKMF) computer simulations, we reveal some of the reasons why this is the case. First of all, even the expressions "phase diagram" and "phase composition" are usually not well-defined. We show the two different types of phase diagrams that are rarely distinguished. For phase separating nanoparticles, one diagram shows the equilibrium phase compositions in two-phase state while the other represents if the system is in an alloyed or in a separated state. We calculate both diagrams for the case of binary Janus nanoparticles and show their dependences on size and average composition. The equilibrium compositions of the phases change with both the size and the average composition of the particle. This means that the use of 3D phase diagrams is unavoidable even if the size of the particle is fixed. The careful investigation of the simulation results reveals the essential role that the interfaces play in the behaviour of the system hence in the shape of the phase diagrams. We also point out that the methods used to determine the phase compositions in nanoparticles have a substantial influence on the details of both experimentally and theoretically constructed phase diagrams.
事实证明，确定纳米颗粒的二元相图是一项非常困难的任务，无论尝试通过计算机模拟、理论考量还是实验来进行。在这项工作中，我们使用三维物体随机动力学建模框架（3DO-SKMF）进行计算机模拟，揭示了其中的一些原因。首先，即使是“相图”和“相组成”这些表述通常也没有明确的定义。我们展示了两种很少被区分的不同类型的相图。对于相分离纳米颗粒，一种相图显示两相状态下的平衡相组成，而另一种表示系统处于合金化状态还是分离状态。我们计算了二元Janus纳米颗粒情况下的这两种相图，并展示了它们对尺寸和平均组成的依赖性。相的平衡组成随颗粒的尺寸和平均组成而变化。这意味着即使颗粒尺寸固定，使用三维相图也是不可避免的。对模拟结果的仔细研究揭示了界面在系统行为中以及因此在相图形状中所起的关键作用。我们还指出，用于确定纳米颗粒中相组成的方法对实验构建和理论构建的相图的细节都有重大影响。
