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Molecular dynamics study of oxygen self-diffusion in reduced CeO2
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
2007 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 178, no 25-26, 1421-1427 p.Article in journal (Refereed) Published
Abstract [en]

The oxygen self-diffusion in partially reduced CeO2 has been investigated by large-scale Molecular Dynamics simulations, in the temperature range between 800 and 2200 K. Simulation boxes with ~ 4100 and ~ 33,000 ions were investigated for randomly distributed oxygen vacancies and Ce3+ ions. Our calculated self-diffusion coefficients vary between 10−8 and 10−6 cm2/s in the temperature range studied. The activation energy and D0 values are also reported. The oxygen diffusion mechanism has also been analyzed: only a 100 vacancy mechanism is observed.

Place, publisher, year, edition, pages
2007. Vol. 178, no 25-26, 1421-1427 p.
Keyword [en]
Diffusion, Molecular dynamics, Cerium dioxide
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-12092DOI: 10.1016/j.ssi.2007.08.003ISI: 000251539600001OAI: oai:DiVA.org:uu-12092DiVA: diva2:39861
Available from: 2007-11-26 Created: 2007-11-26 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Dynamics in Ceria and Related Materials from Molecular Dynamics and Lattice Dynamics
Open this publication in new window or tab >>Dynamics in Ceria and Related Materials from Molecular Dynamics and Lattice Dynamics
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In discussions of heterogeneous catalysis and other surface-related phenomena, the dynamical properties of the catalytic material are often neglected, even at elevated temperatures. An example is the three-way catalyst (TWC), used for treatment of exhaust gases from combustion engines operating at several hundred degrees Celsius. In the TWC, reduced ceria (CeO2-x) is one of the key components, where it functions as an oxygen buffer, storing and releasing oxygen to provide optimal conditions for the catalytic conversion of the pollutants. In this process it is evident that dynamics plays a crucial role, not only ionic vibrations, but also oxygen diffusion.

In this thesis, the structure and dynamics of several ionic crystalline compounds and their surfaces have been studied by means of Molecular dynamics (MD) simulations and Lattice dynamics (LD) calculations. The main focus lies on CeO2-x, but also CeO2, MgO and CaF2 have been investigated.

The presence of oxygen vacancies in ceria is found to lead to significant distortions of the oxygen framework around the defect (but not of the cerium framework). As a consequence, a new O-O distance emerges, as well as a significantly broadened Ce-O distance distribution.

The presence of oxygen vacancies in ceria also leads to increased dynamics. The oxygen self-diffusion in reduced ceria was calculated from MD simulations in the temperature range 800-2000 K, and was found to follow an Arrhenius behaviour with a vacancy mechanism along the crystallographic <100> directions only.

The cation and anion vibrational surface dynamics were investigated for MgO (001) using DFT-LD and for CaF2 (111) in a combined LEED and MD study. Specific surface modes were found for MgO and increased surface dynamics was found both experimentally and theoretically for CaF2, which is isostructural with CeO2.

Many methodological aspects of modeling dynamics in ionic solids are also covered in this thesis. In many cases, the representation of the model system (slab thickness, simulation box-size and the choice of ensemble) was found to have a significant influence on the results.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 48 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 249
Keyword
Inorganic chemistry, molecular dynamics, diffusion, surface dynamics, ionic surfaces, Oorganisk kemi
Identifiers
urn:nbn:se:uu:diva-7374 (URN)91-554-6746-6 (ISBN)
Public defence
2006-12-19, Häggsalen, The Ångström Laboratory, Uppsala, 10:15
Opponent
Supervisors
Available from: 2006-11-28 Created: 2006-11-28 Last updated: 2014-01-28Bibliographically approved

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Spångberg, DanielHermansson, Kersti

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