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Electronic and elastic properties of CaF2 under high pressure from ab initio calculations
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2009 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, no 41Article in journal (Refereed) Published
Abstract [en]

Calcium fluoride CaF2 has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF2 is the fluorite structure (Fm (3) over barm), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni2In-type structure (P6(3)/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the (Fm (3) over barm) and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine p(z)-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the c(h) (or a(o)) direction for the orthorhombic phase is stronger than that in the hexagonal crystal.

Place, publisher, year, edition, pages
2009. Vol. 21, no 41
Keyword [en]
augmented-wave method, optical-properties, fluorite caf2, phase, crystal, transformation, constants, solids
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-18787DOI: 10.1088/0953-8984/21/41/415501ISI: 000270110000009Scopus ID: 2-s2.0-70349331505OAI: oai:DiVA.org:kth-18787DiVA: diva2:336834
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 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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