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Thermal properties of materials from first principles
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the search of clean and efficient energy sources intermediate temperature solid oxide fuel cells are among the prime candidates. What sets the limit of their efficiency is the solid electrolyte. A promising material for the electrolyte is ceria. This thesis aims to improve the characteristics of these electrolytes and help provide thorough physical understanding of the processes involved. This is realised using first principles calculations.

The class of methods based on density functional theory generally ignores temperature effects. To accurately describe the intermediate temperature characteristics I have made adjustments to existing frameworks and developed a qualitatively new method. The new technique, the high temperature effective potential method, is a general theory. The validity is proven on a number of model systems.

Other subprojects include low-dimensional segregation effects, adjustments to defect concentration formalism and optimisations of ionic conductivity.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 62 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1453
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-78755ISBN: 978-91-7519-884-2 (print)OAI: oai:DiVA.org:liu-78755DiVA: diva2:535576
Public defence
2012-06-15, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 14:00 (English)
Opponent
Supervisors
Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2012-06-20Bibliographically approved
List of papers
1. Lattice dynamics of anharmonic solids from first principles
Open this publication in new window or tab >>Lattice dynamics of anharmonic solids from first principles
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 18, 180301- p.Article in journal (Refereed) Published
Abstract [en]

An accurate and easily extendable method to deal with lattice dynamics of solids is offered. It is based on first-principles molecular dynamics simulations and provides a consistent way to extract the best possible harmonic-or higher order-potential energy surface at finite temperatures. It is designed to work even for strongly anharmonic systems where the traditional quasiharmonic approximation fails. The accuracy and convergence of the method are controlled in a straightforward way. Excellent agreement of the calculated phonon dispersion relations at finite temperature with experimental results for bcc Li and bcc Zr is demonstrated.

Place, publisher, year, edition, pages
American Physical Society, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-72810 (URN)10.1103/PhysRevB.84.180301 (DOI)000297099800001 ()
Note
Funding Agencies|Swedish Research Council (VR)||Available from: 2011-12-09 Created: 2011-12-08 Last updated: 2017-12-08
2. Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures
Open this publication in new window or tab >>Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures
Show others...
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, 125406-1-125406-7 p.Article in journal (Refereed) Published
Abstract [en]

We study the structural properties of ultrathin AgxPd1−x films on top of a Ru(0001) substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer (4-ML) Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.

Place, publisher, year, edition, pages
APS, 2008
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44362 (URN)10.1103/PhysRevB.77.125406 (DOI)76396 (Local ID)76396 (Archive number)76396 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13Bibliographically approved
3. Charge Redistribution Mechanisms of Ceria Reduction
Open this publication in new window or tab >>Charge Redistribution Mechanisms of Ceria Reduction
2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 13, 135504- p.Article in journal (Refereed) Published
Abstract [en]

Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities.

Place, publisher, year, edition, pages
American Physical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76952 (URN)10.1103/PhysRevLett.108.135504 (DOI)000302173000017 ()
Note
Funding Agencies|Swedish Research Council, (VR)||Swedish Government||Available from: 2012-05-02 Created: 2012-04-27 Last updated: 2017-12-07
4. Tuning ionic conductivity in ceria by volume optimization
Open this publication in new window or tab >>Tuning ionic conductivity in ceria by volume optimization
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Effect of volume change on the ionic conductivity in ceria has been studied in the framework of the density functional theory. We show that properly controlling external conditions one can treat the lattice constant of ceria as an adjustable parameter and change the topology of the energy landscape for the oxygen ion diffusion. We reveal the existence of the narrow range of lattice parameters, which optimize the ionic conductivity in ceria.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78752 (URN)
Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2012-06-20Bibliographically approved
5. Temperature dependent effective potential method for accurate free energy calculation of solids
Open this publication in new window or tab >>Temperature dependent effective potential method for accurate free energy calculation of solids
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We have developed a thorough and accurate method of determining anharmonic free energies. The technique is based in ab initio molecular dynamics and map a model Hamiltonian to the fully anharmonic system. We can accurately deal with low-symmetry systems, such as random alloys. The formalism and the numerics are described in great detail. A number of practical examples are given, and favourable results are presented, both with respect to experiment and established techniques.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78753 (URN)
Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2012-06-20Bibliographically approved
6. Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations
Open this publication in new window or tab >>Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations
Show others...
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 9Article in journal (Refereed) Published
Abstract [en]

Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. First-principles simulations are based on ab initio molecular dynamics (AIMD). Computational efficiency of the method is greatly enhanced by a careful preparation of the initial state of the simulation cell that minimizes or completely removes a need for equilibration and therefore allows for parallel AIMD calculations. Elastic constants C11, C12, and C44 are calculated. A strong dependence on the temperature is predicted, with C11 decreasing by more than 29% at 1800 K as compared to its value obtained at T=0 K. Furthermore, we analyze the effect of temperature on the elastic properties of polycrystalline TiN in terms of the bulk and shear moduli, the Young's modulus and Poisson ratio. We construct sound velocity anisotropy maps, investigate the temperature dependence of elastic anisotropy of TiN, and observe that the material becomes substantially more isotropic at high temperatures. Our results unambiguously demonstrate the importance of taking into account finite temperature effects in theoretical calculations of elastic properties of materials intended for high-temperature applications.

Place, publisher, year, edition, pages
American Physical Society, 2013
National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-78754 (URN)10.1103/PhysRevB.87.094114 (DOI)000316791600001 ()
Note

Funding Agencies|Swedish Research Council|621-2008-5535621-2011-4426|Swedish Foundation for Strategic Research (SSF) programs|10-0026|project Designed Multicomponent Coatings (MultiFilms)||Erasmus Mundus doctoral program DocMase||Ministry of Education and Science of the Russian Federation within the framework of Program Research and Pedagogical Personnel for Innovative Russia|14.B37.21.089010.09.2012|

Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2017-12-07Bibliographically approved

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