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Ab initio prediction of high-pressure structural phase transition in BaH2
2007 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 446, 405-408 p.Article in journal (Refereed) Published
Abstract [en]

We have performed ab initio electronic structure calculations to calculate the structural properties and high-pressure phase transition in Barium dihydride (BaH2). Our results show that BaH2 crystallizes the orthorhombic phase (CoSi2-type structure) with Pnma space group at ambient conditions. A phase transition to the hexagonal (Ni2In-type structure) with P6(3)/mmc space group is found at pressure around 4 GPa. At the phase transition, the coordination number of hydrogen increases from 9 to 11 and the average bond length of Ba-H increases. The results show a band gap of 2.9 eV for orthorhombic and 1.8 eV for hexagonal phase. In addition, it was also found that more energy is required to desorb hydrogen atom from high-pressure phase as compared to ambient phase.

Place, publisher, year, edition, pages
2007. Vol. 446, 405-408 p.
Keyword [en]
Earth metal-hydrides, neutron-diffraction, crystal-structure
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-24676DOI: 10.1016/j.jallcom.2006.12.103ISI: 000250822900086OAI: oai:DiVA.org:kth-24676DiVA: diva2:352711
Note
QC 20100921Available from: 2010-09-22 Created: 2010-09-21 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Theoretical Investigations of Compressed Materials
Open this publication in new window or tab >>Theoretical Investigations of Compressed Materials
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of high pressure as a tool to design new materials as well as to investigatematerials properties has become increasingly important during last one decade. The maingoal of the present thesis is to enhance the significance of the high pressure method as aquantitative tool in solid state investigations. Virtually all of the properties of solids aredirectly determined by their electronic structure. Similarly, the changes in the propertiesof solids under pressure are determined by the changes in the electronic structure underpressure. We have attempted to provide a comprehensive description of the resulting theoryin a electronic structure and the properties of condensed matter.

The theoretical basis for these investigations is the density functional theory, in combinationwith ab initio method. The study of pressure induced phase transitions for thecompounds of CaF2, Cr2GeC, Ti3SiC2, as well as V at 0 K are presented. The latticeparameters, the phase transition pressures, the equation of states, the electronic structureshave been calculated and shown a good agreement with experimental results.

A lattices dynamic study of the body center cubic (bcc) Fe under high pressure andhigh temperature is presented. The bcc iron could dynamical stabilize in the Earth innercore conditions. The unusual phase transition of bcc V under high pressure is investigatedand it is shown that the driving mechanism is electron-phonon interaction.

Finally, a method based on the LDA+U approach has been applied to study spin statetransition in FeCO3. Our results show that magnetic entropy play a significant role in spinstate transition.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 34 p.
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-24641 (URN)9789174157352 (ISBN)
Public defence
2010-10-08, Sal D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100920Available from: 2010-09-20 Created: 2010-09-20 Last updated: 2010-09-22Bibliographically approved

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