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Unusual lattice dynamics of vanadium under high pressure
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2007 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, no 42, 16428-16431 p.Article in journal (Refereed) Published
Abstract [en]

The electronic structures and lattice dynamics of pressure-induced complex phase transitions [bcc -> hRl(110.5 degrees) -> distorted-hRl(108.2') -> bcc] in vanadium as a function of pressure up to 400 GPa have been investigated with an ab initio method using density functional perturbation theory (DFPT). At ambient pressure, the soft transverse acoustic phonon mode corresponding to Kohn anomaly appears at a wave vector q = 2k(F) along [xi 00] Gamma -> H high symmetry direction. The nonclegenerate transverse acoustic branches TA(1) on < 110 > and TA(2) on < 001 > show an exceptionally large split at high symmetry point N (0.5 0.5 0.0). The lattice dynamical instability starts at a pressure of 62 GPa (V/V-0 = 0.78, where V-0 is experimental volume of bcc-V at ambient conditions), derived by phonon softening that results in phase transition of bcc -> hR1 (alpha = 110.5 degrees). At compression around 130 GPa (V/V-0 = 0.67), the rhombohedral angle of hR1 phase changed to 108.2 degrees, and the electronic structure changed drastically. At even higher pressure, approximate to 250 GPa (V/V-0 = 0.57), lattice dynamic calculations show that the bcc structure becomes stable again.

Place, publisher, year, edition, pages
2007. Vol. 104, no 42, 16428-16431 p.
Keyword [en]
ab initio calculation, phonon, structure phase transition, phonon-dispersion, pseudopotentials
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-17061DOI: 10.1073/pnas.0707377104ISI: 000250373400010Scopus ID: 2-s2.0-36749027665OAI: oai:DiVA.org:kth-17061DiVA: diva2:335104
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-09-22Bibliographically 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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