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Ab initio based investigation of the oxygen and nitrogen interstitial ordering in hcp Hf, Zr, and Ti: An ab initio study
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.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, 134110- p.Article in journal (Refereed) Published
Abstract [en]

We investigate the ordering of oxygen and nitrogen interstitials in hcp Zr, Hf, and Ti using the corresponding oxygen-oxygen and nitrogen-nitrogen interactions obtained in the state-of-the-art first-principles calculations. Two main contributions, chemical and strain induced, to the interstitial-interstitial interactions are obtained by different techniques. We find that there is the strong repulsion between interstitial atoms at the nearest-and next-nearest-neighbor coordination shells, which is solely determined by the chemical interaction determined on a fixed ideal lattice, while both contributions are important for more distant coordination shells. The Monte Carlo simulations reveal the existence of three stoichiometric compositions, MeI1/6, MeI1/3, and MeI1/2, for the ground-state structures of interstitials, having different ordering types. Our results for the structures of oxygen interstitials are in good agreement with existing experimental data for the Ti and Hf alloys. In the case of Zr-O interstitial alloys, we correctly predict the general type of ordering, although the detailed structure is at variance the experimental observations. The ordering transition temperatures in some cases are overestimated by a factor of 2. We also predict the ordering type of nitrogen interstitials in hcp Ti, Zr, and Hf, which are similar to those in the case of oxygen interstitials.

Place, publisher, year, edition, pages
2010. Vol. 82, no 13, 134110- p.
Keyword [en]
O SOLID SOLUTION; HEAT-CAPACITY MEASUREMENT; DISORDER TRANSFORMATION; POTENTIAL MODEL; ALLOYS; TRANSITION; METALS; TITANIUM; ATOMS; APPROXIMATION
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7897DOI: 10.1103/PhysRevB.82.134110ISI: 000282937600001Scopus ID: 2-s2.0-78049404211OAI: oai:DiVA.org:kth-7897DiVA: diva2:13061
Note
QC 20100624 Uppdaterat från manuskript till artikel 20110106Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2012-03-19Bibliographically approved
In thesis
1. Point defect interactions and structural stability of compounds
Open this publication in new window or tab >>Point defect interactions and structural stability of compounds
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Theoretical studies of point defect interactions and structural stability of compounds have been performed using density functional theory. The defect-related properties, such as activation energy of diffusion, electronic and magnetic structure of selected materials have been studied.

The major part of the present work is devoted to a very important material for semiconductor industry, GaAs. The formation energies of intrinsic point defects and the solution energies of 3d transitions in GaAs have been calculated from first principles. Based on the calculated energies, we analysed the site preference of defects in the crystal. The tendency of defects to form clusters has been investigated for the intrinsic defects as well as for impurities in GaAs. The magnetic moment of 3d impurities has been calculated as a function of the chemical environment. The possibility of increasing the Curie temperature in (Ga,Mn)As by co-doping it with Cr impurities has been examined on the basis of calculated total energy difference between the disordered local moment and the ferromagnetically ordered spin configurations. We found that, in order to reach the highest critical temperature, GaAs should be separately doped with either Cr or Mn impurities. Also, we have shown that diffusion barrier of interstitial Mn depends on the charge state of this impurity in (Ga, Mn)As. The formation of defect complexes between interstitial and substitutional Mn atoms, and their influence on the value of diffusion barrier for interstitial Mn, has been studied.

The pair interactions energies between interstitial oxygen atoms in hcp Zr, Hf and Ti have been calculated using first principles. Based on the calculated energies, the oxygen ordering structures in IVB transition metal solid solutions have been explained. A prediction of nitrogen ordering in Hf-N solid solution has been made.

The thermodynamic description of intermetallic compounds in the Zr-Sn binary system has been obtained. The conclusion has been made that Zr substitution on the Sn sites takes place in the Zr4Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound.

The influence of pressure on the phase stability in the Fe-Si system has been investigated. We have found instability of the hcp Fe0.9Si0.1 random alloy with respect to the decomposition onto the Si-poor hcp Fe alloy and the B2 FeSi under high pressure. The tendency of this decomposition becomes stronger with increasing the applied pressure.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007
Keyword
first principles, ab initio, density functional theory, point defects interactions, diluted magnetic semiconductors, structural stability, zirconium alloys
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4605 (URN)978-91-7178-842-9 (ISBN)
Public defence
2008-01-28, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100624Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2012-03-19Bibliographically approved

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