Relationship between composition, structure and conductivity in ceramic oxygen ion conductors with interstitial mechanism

• Applicant: Professor Dr. Steffen Neitzel-Grieshammer
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 338212203

Solid oxide fuel cells and solid oxide electrolyzer cells allow the direct conversion of chemical to electrical energy and vice versa. Prerequisite for the efficient operation of these cells are solid electrolytes with high oxygen ion conductivity. In common oxygen ion conductors oxygen transport is enabled by oxygen vacancies, while in recent years oxygen ion conductors with an interstitial mechanism have gained increasing attention.In the present project, oxygen ion conductors of various compositions with an interstitial mechanism will be investigated with computational methods. As promising materials apatite- and melilite-structured ion conductors will be investigated, which exhibit high oxygen ion conductivity in experiments. Besides the theoretical and experimental studies on these types of materials only a small fraction of all possible compositions has been investigated and a large number of scientific questions still has to be answered. Therefore, in this study, these materials will be investigated systematically and compositions with highest oxygen ion conductivities are to be identified. The present project is divided into three stages. At the first stage, the structures of various compositions are optimized applying density functional theory calculations and the influence of the composition on the local structure is identified. At the second stage, the migration barriers for interstitial ions are calculated and are fitted to the structural parameters by suitable regression methods. In this way, a relationship between structural parameters and migration energies is established and an efficient screening process for oxygen ion conductors with low migration barriers and high conductivities is possible. At the third stage, the ionic conductivity of promising materials is simulated to identify materials with highest oxygen ion conductivities.The project focuses on two aspects: i) Deeper insight into conduction mechanisms and the relation between structure and conductivity. ii) Prediction of the conductivity of yet unknown compositions.In this context, a successive screening is applied to decrease the computational demand by estimating the migration energy, which is costly to calculate, from the structural parameters of the equilibrium structures. At the end of the project the oxygen ion conductivity of materials can be estimated based on the composition and the structure and the prediction of compositions with high ionic conductivity is possible.

• DFG Programme: Research Grants
• International Connection: Japan
• Cooperation Partner: Professor Masanobu Nakayama, Ph.D.