Project Details
Projekt
Charge attachment induced transport (CAIT) studies of energy landscapes in ion conducting solids (Quantification of populated site energy distribution in amorphous and crystalline materials)
Applicant
Professor Dr. Karl-Michael Weitzel
Subject Area
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 428906592
The potential energy landscape of mobile ions in solid-state materials and the atomic scale structure are intimately interrelated and determine the function, e.g. ion transport and hardness. Within this project P1 of the research unit FOR5065 the potential energy landscape of ion conducting solids is investigated by a combination of different ion exchange experiments, in particular the charge attachment induced transport (CAIT) and the alkali proton substitution (APS) with the time-of-flight secondary ion mass spectrometry (ToF-SIMS) technique. The goal is the determination of site energy distributions (SED) in the solid as a function of the structural order, i.e. for amorphous, and crystalline samples as well as samples characterized by unique interfaces, e.g. bicrystals. As materials with model character the focus will be on alkali silicates and strontium titanate, and derivatives thereof. For amorphous samples (e.g. silicate glasses) electric field assisted ion exchange experiments imprints concentration depth profiles into the sample which are subsequently quantified by means of ToF-SIMS in combination with Nernst-Planck-Poisson theory. Ultimately, this yields the populated part of the site energy distribution (PSED), which will be directly compared to the distribution of activation energies, g(Eact) derived from solid state NMR (P2 Vogel) and to the saddle point distribution (SPD) derived from molecular dynamics calculations (P7 Heuer). The direct combination of PSED, g(Eact) and SPD information is expected to provide a significantly improved understanding of the energy landscape – transport dynamics in ion conducting solids. For the crystalline and bicrystalline samples the PSED is – to first approximation – a delta function with respect to one mobile ion species. Here, the focus will be on the interrelation between the macroscopic transport coefficients measured with SIMS and the atomically resolved structure derived from HR-TEM (P4 Jooss), APT (P3 Volkert), the charge state verification by XPS and HAXPES (P8 Gottfried) and multi-scale theory (P6 Jacob). Particular attention will be given to a systematic variation of the orientation of transport and probing the result of transport relative to the orientation of a single grain boundary or interfacial boundary. A second focus will be on the systematic variation of defect concentration. As a result we expect to reach a unified understanding bridging atomically resolved information to macroscopic information for structure, energy and function. To this end, the samples of interest are exchanged between the experimental groups (P1, P2, P3, P4, P8) and the theoretical results will be exchanged with the two theory groups (P6 and P7). Ultimately, this work is expected to lead to an improved understanding of the potential energy landscape in ion conducting solids and its interrelation with atomistic structure and macroscopic transport function.
DFG Programme
Research Units
