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The relation between defect interactions, local structure and oxygen ion conductivity in the bulk of fluorite-structured oxides
For the development of solid oxide fuel cells, SOFC, and high-temperature electrolysis, SOEC, an electrolyte which has a high oxygen ion conductivity is required. Potential candidates are fluorite-structured oxides such as doped zirconia and doped ceria. The latter allows a reduction in the operating temperature from 900 °C to 600 °C and is therefore the main focus of this work. The central aim of this project is the detailed understanding of the relationship between defect interactions, the local structure and the macroscopic oxygen ion conductivity in the bulk of fluorite-structured oxides. By combining ab initio density functional theory, DFT, with Kinetic Monte Carlo simulations, KMC, both the local structure and the oxygen ion conductivity should be predict as a function of doping concentration. These results are verified by accompanying experiments such as Extended X-Ray Absorption Fine Structure (EXAFS) and impedance spectroscopy measurements. In this way, a deeper understanding of the underlying mechanisms is obtained in order to make better predictions about material properties.
J. Koettgen, P. C. Schmidt, T. Bučko, M. Martin, Ab initio calculation of the migration free energy of oxygen diffusion in pure and samarium-doped ceria, Phys. Rev. B 97 (2018) 024305.
J. Koettgen, T. Zacherle, S. Grieshammer, M. Martin, Ab initio calculation of the attempt frequency of oxygen diffusion in pure and samarium doped ceria, Phys. Chem. Chem. Phys. 19 (2017) 9957-9973.
J.R. Köttgen, The relation between defect interactions, local structure and oxygen ion conductivity in the bulk of doped ceria, Dissertation, RWTH Aachen University, 2017.
M. Martin, R. A. De Souza, J. Köttgen, F. Draber, P. Hein, Defects and diffusion in solids: Application of new theoretical concepts, Bunsen-Magazin 19.3 (2017) 138-139.
S. Grieshammer, B.O.H. Grope, J. Koettgen, M. Martin, A combined DFT+U and Monte Carlo study on rare earth doped ceria, Phys. Chem. Chem. Phys. 16 (2014) 9974-9986.
T. Leichtweiss, R.A. Henning, J. Koettgen, R.M. Schmidt, B. Holländer, M. Martin, M. Wuttig, J. Janek, Amorphous and highly nonstoichiometric titania (TiOx) thin films close to metal-like conductivity, J. Mater. Chem. A 2 (2014) 6631-6640.
M. Lumeij, J. Koettgen, M. Gilleßen, T. Itoh, R. Dronskowski, Detailed insights into the structural properties and oxygen-pathways in orthorhombic Ba0.5Sr0.5Co0.8Fe0.2O3–δ by electronic-structure theory, Solid State Ionics Vol. 222-223 (2012) 53-58.