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Ionic conductivity in Sm-doped ceria from first-principles non-equilibrium molecular dynamics
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.ORCID iD: 0000-0002-3933-9066
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0001-6083-091X
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
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2016 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 296, 47-53 p.Article in journal (Refereed) Published
Abstract [en]

Sm-doped ceria is a prospective electrolyte material for intermediate-temperature solid-oxide fuel cells (IT-SOFC). Equi- librium ab initio molecular dynamics (AIMD) studies of oxygen ion diffusion in this material are currently impractical due to the rareness of diffusive events on the accessible timescale. To overcome this issue we have performed ab ini- tio non-equilibrium molecular dynamics calculations of Sm-doped ceria using the color-diffusion algorithm. Applying an external force field we have been able to increase the frequency of diffusive events over the simulation time, while keeping the physical mechanism of diffusion intact. We have investigated the temperature dependence of the maximum strength of the applied external field that could be used while maintaining the response of the system in a linear regime. This allows one to obtain the diffusivity at zero field. The bulk ionic conductivity has been calculated and found to match the experimental data well. We have also compared the description of the diffusion process by our method to previous findings and show that the migration mechanism and site preference of oxygen vacancies with respect to the Sm dopants is well reproduced. 

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 296, 47-53 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-192499DOI: 10.1016/j.ssi.2016.08.011OAI: oai:DiVA.org:kth-192499DiVA: diva2:968976
Note

QC 20160913

Available from: 2016-09-13 Created: 2016-09-13 Last updated: 2016-09-13Bibliographically approved
In thesis
1. First-principles studies of kinetic effects in energy-related materials
Open this publication in new window or tab >>First-principles studies of kinetic effects in energy-related materials
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum mechanical calculations based on first-principles (lat. ab initio) methods have over the past decades proved very successful for the study of many materials properties. Based solely on the fundamental constants of physics, the strength of these methods lies not only in describing existing materials, but also in predicting completely new ones. This thesis contains work both related to the quest for improved materials, and to the development of new methods.

Equilibrium ab initio molecular dynamics methods are powerful for simulating diffusion in solids but are accompanied with high computational costs. This is related to the inherent slowness of the diffusion process in solids. To tackle this problem, we implement the color-diffusion algorithm into the Vienna ab initio simulation package to perform non-equilibrium ab initio molecular dynamics (NEMD) simulations. Ion diffusion in ceria doped with Gd and Sm is studied, and the calculated conductivities is found to agree well with experiment. However, although the NEMD method significantly lowers the computational cost, statistical quality in the calculated conductivity still comes expensive. Knowing the error resulting from limited statistics is therefore important.

We derive an analytical expression for the error in calculated ion conductivity, which is verified numerically using the Kinetic Monte Carlo (KMC) method. Being developed particularly for the simulation of slow events, the great advantage of the KMC method over the NEMD method is that it is much less computationally expensive. This allows for long simulation times and large system sizes. The effect of dopant type and dopant distribution on the oxygen ion diffusivity is investigated with KMC simulations of rare-earth doped ceria. The full set of diffusion barriers in the simulation cell is calculated from first-principles within a density functional theory (DFT) framework.

This Thesis also includes a study of processes involving water on a rutile TiO2(110) surface. The basic processes are: diffusion, dissociation, recombination, and clustering of water molecules. The barriers for these processes are calculated with DFT employing different exchange-correlation (XC) functionals. Using the barriers calculated from two XC functionals, we perform KMC simulations and find that the choice of XC functional radically alters the dynamics of the simulated water-titania system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 68 p.
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-192343 (URN)9789177291022 (ISBN)
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Public defence
2016-10-07, F3, Lindstedsvägen 26, Stockholm, 09:00 (English)
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Note

QC 20160913

Available from: 2016-09-13 Created: 2016-09-09 Last updated: 2016-09-13Bibliographically approved

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