Change search
ReferencesLink to record
Permanent link

Direct link
Self-diffusion in MgO-a density functional study
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
2011 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 34, 345402- p.Article in journal (Refereed) Published
Abstract [en]

Density functional theory calculations have been performed to study self-diffusion in magnesium oxide, a model material for a wide range of ionic compounds. Formation energies and entropies of Schottky defects and divacancies were obtained by means of total energy and phonon calculations in supercell configurations. Transition state theory was used to estimate defect migration rates, with migration energies taken from static calculations, and the corresponding frequency factors estimated from the phonon spectrum. In all static calculations we corrected for image effects using either a multipole expansion or an extrapolation to the low concentration limit. It is shown that both methods give similar results. The results for self-diffusion of Mg and O confirm the previously established picture, namely that in materials of nominal purity, Mg diffuses extrinsically by a single vacancy mechanism, while O diffuses intrinsically by a divacancy mechanism. Quantitatively, the current results are in very good agreement with experiments concerning O diffusion, while for Mg the absolute diffusion rate is generally underestimated by a factor of 5-10. The reason for this discrepancy is discussed.

Place, publisher, year, edition, pages
2011. Vol. 23, no 34, 345402- p.
Keyword [en]
National Category
Condensed Matter Physics
URN: urn:nbn:se:kth:diva-39014DOI: 10.1088/0953-8984/23/34/345402ISI: 000294061500007ScopusID: 2-s2.0-80051930670OAI: diva2:439165
Available from: 2011-09-06 Created: 2011-09-06 Last updated: 2012-03-12Bibliographically approved
In thesis
1. Helium Filled Bubbles in Solids: Nucleation, Growth and Swelling
Open this publication in new window or tab >>Helium Filled Bubbles in Solids: Nucleation, Growth and Swelling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Heliumfyllda bubblor i fasta material : Kärnbildning, tillväxt och svällning
Abstract [en]

When nuclear fuel, fabricated for the purpose of transmuting spent fuel is irradiated, significant amounts of He is produced from alpha particles mainly emitted when 242Cm decays into 238Pu. From irradiation experiments it is known that the presence of He in the solids alters the swelling behaviour of the material. The thesis presents the theoretical background from which nucleation models of He bubbles can be formulated. Such models are presented for He in metals, and the case of He in Mo is studied as an example. MgO, which together with Mo is suggested as a matrix material in transmutation fuel is also studied and the stability of He containing bubbles in this material is discussed.

By calculating parameters for a rate theory model derived from atomistic modelling, it is shown that He can stabilise vacancy clusters and cause cluster growth at temperatures and irradiation doses where nucleation and growth would not otherwise occur. At the initial stages of nucleation He can stabilise small bubbles while larger bubbles are unstable. This results in an incubation time of swelling, which implies that He does not always cause increased swelling, but can at certain irradiation conditions slow down the growth of large vacancy clusters and thereby delay swell\-ing beyond the time of the irradiation.

When comparing the behaviour of bubble nucleation in Mo and MgO, it is found that He has a significant impact even at very low concentrations in Mo. In contrast, the concentration of He has to be considerably higher in MgO to affect the swelling behaviour. For an inert matrix fuel, designed for transmutation purposes, this implies that the Mo matrix will have a tendency to swell considerably at rather high temperatures due to He stabilised vacancy clusters. If operated at lower temperatures, the swelling could instead be reduced due to the incubation time. In a MgO matrix, the swelling behaviour will instead depend largely on the production rate of He. For a low production rate, the material will have a swelling behaviour similar to the one seen when He is not present in the material. A high production rate implies that He will remain in vacancy clusters, thereby stabilising the clusters and enhancing the growth and swelling.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 83 p.
Trita-FYS, ISSN 0280-316X ; 2012:06
Helium, Radiation Damage, DFT, molybdenum, MgO
National Category
Condensed Matter Physics
urn:nbn:se:kth:diva-90960 (URN)978-91-7501-263-6 (ISBN)
Public defence
2012-04-04, F3, Lindstedtsvägen 23, KTH, Stockholm, 13:00 (English)
Available from: 2012-03-12 Created: 2012-03-05 Last updated: 2012-03-12Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Runevall, OddSandberg, Nils
By organisation
Reactor Physics
In the same journal
Journal of Physics: Condensed Matter
Condensed Matter Physics

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 27 hits
ReferencesLink to record
Permanent link

Direct link