Theoretical studies on the ion migration through crystalline materials

离子或原子在固体材料表面或通过固体材料的迁移和扩散不仅对我们对迁移率的基本理解感兴趣，而且对于从燃料电池上的电荷存储设备、膜、聚合物、传感器等各种应用都是有意义的。虽然已经开发了不同的实验技术来获得对此类事件的原子解析的洞察，但原子建模通常限于相当有限和理想化的模型系统。然而，要真正捕捉到现实材料中离子迁移的全部复杂性，需要一个能够描述依赖于浓度的迁移过程以及结构多样性的多尺度方法，例如缺陷或晶界。本项目的目标是研究结构(和组成)之间的关系对阳离子物种的扩散行为的影响，并解决这些固体材料中复杂的势能图景。基于块体材料的结构信息以及HR-TEM(P4 Jooss)和原子探针层析(P3 Volkert)提供的明确的晶界(双晶)，我们将首先使用第一性原理方法(特别是密度泛函理论)研究各个块体系统的形态和电子结构。然后，所获得的信息将被用于优化反应力场，用于随后在不同条件(例如，温度、离子负载、晶格缺陷等)下对系统动力学进行宏正则分子动力学(GC-MD)模拟。在这里，我们已经能够研究与离子储存库接触的块体系统和晶界。这些模拟将提供对材料势能格局以及离子和电子电荷迁移率的作用的见解，这些信息可以与实验性的ToF-SIMS研究(P1 Weitzel)研究相比较。此外，观察到的离子在材料中的分布可以与结构APT(P3 Volkert)和核磁共振(P2 Vogel)分析相比较，而能量学将进入在P1(Weitzel)内进行的平均场模拟和P5(Maass)的蒙特卡罗研究。最后，我们将进行动力学蒙特卡罗模拟，以便在更大的时间和长度尺度上跟踪Cait实验(P1 Weitzel)，其中离子迁移是由浓度梯度引起的。同样，结果将很容易与在P1(Weitzel)中进行的实验以及P3(Volkert)、P4(Jooss)和P2(Vogel)的结构分析相比较。

Migration and diffusion of ions or atoms ontop or through solid materials is of interest not only for our fundamental understanding of mobility but also for various applications ranging from charge storage devices over fuel cells, membranes, polymers, sensors, and many more. While different experimental techniques have been developed to gain even atomically-resolved insights on such events, atomistic modelling is often restricted to rather limited and idealized model systems. However, to really capture the whole complexity of ion migration in realistic materials requires a multi-scale approach that is capable of describing concentration-dependent migration processes as well as structural diversities, e.g. defects or grain boundaries.Focusing on Li-borates as well as on perovskites as model systems that are available as well-defined crystalline materials (P1 Weitzel), the goal of this project is to study the relationship between structure (and composition) on the diffusion behaviour of cationic species and to resolve the complex potential energy landscape in these solid-state materials. Based on structural information on the bulk materials as well as well-defined grain boundaries (bicrystals) provided by the HR-TEM (P4 Jooss) and atom probe tomography (P3 Volkert) we will first study the morphology and electronic structure of the respective bulk systems using first principles methods (in particular DFT). The obtained information will then be used to optimize reactive forcefields for subsequent grand-canonical molecular dynamics (GC-MD) simulations on the system dynamics under varying conditions (e.g. temperature, ion loading, lattice defects, etc.). Here we will already be able to study both bulk systems as well as grain-boundaries in contact with an ion reservoir. These simulations will provide insights into the potential energy landscape of the material as well as the role of ionic and electronic charge mobility, information that can be compared to the experimental ToF-SIMS studies (P1 Weitzel) studies. In addition, the observed ion distribution within the material can be compared to the structural APT (P3 Volkert) and NMR (P2 Vogel) analyses, while the energetics will enter the mean-field simulations performed within P1 (Weitzel) and the Monte-Carlo studies of P5 (Maass). Finally, we will perform kinetic Monte-Carlo simulations in order to follow the CAIT experiment (P1 Weitzel) on larger time- and length-scales, where ion migration is induced by a concentration gradient. Again, the outcome will be readily comparable to the experiments performed in P1 (Weitzel) and the structural analyses of P3 (Volkert), P4 (Jooss) and P2 (Vogel).