FOR 5065 - Subproject: Microscopic perspective on ion transport in amorphous solid ion conductors

Basic data for this project

Description

The complex interplay between potential energy landscapes and atomic-scale structure fundamentally influences ionic motion in solid-state materials. This relationship is of particular importance in modern materials research, especially for energy-related applications. Elucidating these relationships provides a fundamental understanding of these systems and, in the long run, may help to identify possible directions for improving functional materials. In general, simulations of silica systems have already been very helpful in learning about the underlying mechanisms of ion transport in amorphous solid ion conductors below the glass transition. By studying the trajectories, correlated discrete jumps of individual alkali ions in the network structure can be observed. Later, the ion dynamics were described as transitions between well-defined and time-independent sites provided by the silica network. Central to this proposal is the concept of the potential energy landscape (PEL). Studying the PEL for disordered systems can be a very powerful technique to characterize the topology of the local minima as well as their relationship to the resulting dynamical processes. Applying the PEL picture to the lithium silicate system, at the most reduced level one can consider the dynamics of a single lithium ion in the fixed framework provided by the lithium network. The other ions provide only a mean-field background. This corresponds to the particle dynamics in a random 3D PEL. Indeed, many models have been developed to characterize transport in this system. However, corrections to the mean-field picture are very likely already for ambient cation concentrations, so that the static picture of the silicate network needs to be modified. The challenges associated with these aspects are the focus of this project. The work packages planned for the new project P7 deal with the characterization of structural, energetic and dynamical properties of alkali silicate systems in the context of the experiments performed in ELSICS. In particular, a very fruitful interaction with the NMR and CAIT experiments is envisaged. The work packages are organized in three steps. First, we will study individual alkali silicates to elucidate in detail the relationship between energetic and dynamic properties. Next, we will study the properties of mixed alkali systems to explore different possibilities of how two alkali species can share the silica network and how strong the site specificity is. Finally, we plan to simulate the CAIT experiment. Among other things, this will allow us to explicitly test the various hypotheses used to interpret the CAIT experiments. Of particular interest is the effect of site specificity on the dynamical processes in these systems. We focus on lithium, sodium and potassium ions, for which well-tested force fields exist.