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Heavy Metal Compounds and Hydrogen Storage Materials from Ab Initio Calculations
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In principle, most of the properties of solids can be determined by their electronic structures. So the understanding of electronic structures is essential. This thesis presents two classes of materials using ab initio method based on density functional theory. One is heavy metal compounds like Ta2AlC, ThO and the other one is hydrogen storage material namely MgH2 surfaces.

The study of correlation and relativistic effects in Ta2AlC are presented. Based on our results, Ta2AlC is a weakly correlated system. Our study shows that the spin - orbital coupling does not play a very important role where as the other relativistic corrections such as mass velocity and Darwin terms have a significant effect on the electronic properties.

The stability of rock salt like ThO has been proposed based on the first principle calculation. ThO can be stabilized under pressure. The driving force is the sd to f charge transfer in Th.

We have investigated the energetics of hydrogen desorption from the MgH2 (110) and (001) surfaces. The doping of foreign metal elements and strain were used to reduce the dehydrogenation energy. The reduction in dehydrogenation energy is caused by the charge localization on the metal atoms which leads to destabilization and the weakening of metal - hydrogen bonds.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vii, 32 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-120062ISBN: 978-91-7501-675-7 (print)OAI: oai:DiVA.org:kth-120062DiVA: diva2:613306
Presentation
2013-04-10, Sal M131, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130327

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2013-03-27Bibliographically approved
List of papers
1. Role of correlation and relativistic effects in MAX phases
Open this publication in new window or tab >>Role of correlation and relativistic effects in MAX phases
2012 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 47, no 21, 7615-7620 p.Article in journal (Refereed) Published
Abstract [en]

We have performed the ab initio calculations to study the role of correlation and relativistic effects in MAX phases. As of now, there are more than 50 MAX phases reported in the literature; however, we have chosen two MAX phases, namely Cr2AlC and Ta2AlC, as representatives of MAX phases for our study as they are very poorly described from calculation point of view. Our results show that correlation effects are very important to understand the electronic and mechanical properties of Cr2AlC, but not so important for Ta2AlC. We have also studied the relativistic effects on Ta2AlC and our calculations show that going from scalar to fully relativistic effects does not have any significant effect on the electronic and mechanical properties of Ta2AlC. We conclude that Ta2AlC is a weakly correlated system, whereas Cr2AlC is a strongly correlated system. Further experiments are needed to explain the discrepancy between theory and experiments.

Keyword
Generalized Gradient Approximation, Initio Molecular-Dynamics, Band-Structure, Ti3sic2, Cr, Transition, Solids, Ta2alc, Energy, Ta
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-102336 (URN)10.1007/s10853-012-6609-6 (DOI)000307520900026 ()2-s2.0-84865248947 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20120914

Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
2. Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface
Open this publication in new window or tab >>Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface
Show others...
2013 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, no 2, 27006- p.Article in journal (Refereed) Published
Abstract [en]

On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (ΔH) of MgH2 (001) systems have been analyzed. The maximum improvement in ΔH has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of ΔH when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in ΔH. The doping of Ti on MgH 2 (001) is also very beneficial even without strain. The reduction in ΔH is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds.

Keyword
Magnesium Hydride, Ab-Initio, Ti, Storage, Al, Metals, Alloy, Mn
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-119674 (URN)10.1209/0295-5075/101/27006 (DOI)000314677100029 ()2-s2.0-84874136891 (Scopus ID)
Funder
Formas
Note

QC 20130320

Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2017-12-06Bibliographically approved
3. The effects of strain and doping on hydrogen storage material of the MgH2(110) surface
Open this publication in new window or tab >>The effects of strain and doping on hydrogen storage material of the MgH2(110) surface
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-120060 (URN)
Note

QS 2013

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2014-12-19Bibliographically approved
4. The stable rock salt like ThO chemically synthesized under pressure by theory
Open this publication in new window or tab >>The stable rock salt like ThO chemically synthesized under pressure by theory
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The rock salt like ThO was predicted to be stable under pressure by ab initio method. The procedure is applying pressure to the following reaction: Th+ThO2=) ThO. ThO is energetically favored in a range of 14 GPa - 26 GPa by the proof of reaction enthalpy. The lattice dynamic of ThO shows its stability under high pressure. In this reaction, Thorium metal plays signicant role on the reaction by the contributing of the transformation s, d to f orbital occupation. It is found that the lled f electrons mainly are at expense of s electrons. The newly stabilized ThO is metallic. The stabilizer is the hybridization of d - p electrons. The concentration of oxygen bonded to Th induce crystal eld splitting in d and f bands. The lled f electrons do inuence the energy level of d bands. We also found that ThO2 has a indirect band gap at 20 GPa.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-120059 (URN)
Funder
Swedish Research Council
Note

QS 2013

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2013-03-27Bibliographically approved

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