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Describing interstitials in close-packed lattices: first-principles study
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2010. , 32 p.
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-31124ISBN: 978-91-7415-880-9OAI: oai:DiVA.org:kth-31124DiVA: diva2:402781
Presentation
2011-03-25, Konferensrummet, Materialvetenskap, KTH, Brinellvägen 23, Stockholm, 10:00
Note
QC 20110309Available from: 2011-03-09 Created: 2011-03-09 Last updated: 2011-03-09Bibliographically approved
List of papers
1. Completeness of the exact muffin-tin orbitals: application to hydrogenated alloys
Open this publication in new window or tab >>Completeness of the exact muffin-tin orbitals: application to hydrogenated alloys
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 4Article in journal (Refereed) Published
Abstract [en]

We investigate the basis set convergence of the exact muffin-tin orbitals by monitoring the equation of state for Al, Cu, and Rh calculated in the conventional face-centered-cubic lattice (str-I) and in a face-centered-cubic lattice with one atomic and three empty sites per primitive cell (str-II). We demonstrate that three (spd) muffin-tin orbitals are sufficient to describe Al in both structures, but for str-II Cu and Rh at least five (spdfg) orbitals are needed to get converged equilibrium Wigner-Seitz radius (within <= 0.8%) and bulk modulus (<= 3.3%). We ascribe this slow convergence to the nearly spherical densities localized around the Cu and Rh atoms, which create strongly asymmetric charge distributions within the nearest cells around the empty sites. The potential sphere radius dependence of the theoretical results for structure str-II is discussed. It is shown that a properly optimized overlapping muffin-tin potential in combination with the spdfg basis yields acceptable errors in the equilibrium bulk properties. The basis set convergence is also shown on hydrogenated Sc and Sc-based alloys.

Keyword
total-energy calculations, initio molecular-dynamics, wave basis-set, ab-initio, electron-gas, surface-energy, ground-state, metals, approximation, semiconductors
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-19159 (URN)10.1103/PhysRevB.81.045122 (DOI)000274002500053 ()2-s2.0-77954824021 (ScopusID)
Funder
Swedish Research Council
Note
QC 20110121Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-11-18Bibliographically approved
2. Influence of Magnesium on hydrogenated ScAl1-xMgx alloys: a theoretical study
Open this publication in new window or tab >>Influence of Magnesium on hydrogenated ScAl1-xMgx alloys: a theoretical study
2011 (English)In: Computational materials science, ISSN 0927-0256, Vol. 50, no 10, 2848-2853 p.Article in journal (Refereed) Published
Abstract [en]

Ab initio total energy calculations, based on the projector augmented wave method and the exact mu±n-tin orbitals method in combination with the coherent-potential approximation, are used to examine the effect of magnesium on hydrogen absorption/desorption temperature and phase stability of hydrogenated ScAl1-xMgx (0 ≤ x ≤ 0:3) alloys. According to the  experiments, ScAl1-xMgx adopts the CsCl structure, and upon hydrogen absorption it decomposes into ScH2 with CaF2 structure and Al-Mg with face centered cubic structure. Here we demonstrate that the stability field of the hydrogenated alloys depends sensitively on Mg content and on the microstructure of the decomposed system. For a given microstructure, the critical temperature for hydrogen absorption/desorption increases with Mg concentration.

Keyword
Hydrides, Sc-based alloys, Hydrogen storage materials, First-principles calculations
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-31070 (URN)10.1016/j.commatsci.2011.04.040 (DOI)000293486900011 ()2-s2.0-79959506804 (ScopusID)
Funder
Swedish Research CouncilEU, European Research Council
Note
Updated from submitted to published.Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2011-11-18Bibliographically approved
3. The bain path of paramagnetic Fe-Cr based alloys
Open this publication in new window or tab >>The bain path of paramagnetic Fe-Cr based alloys
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 1, 013708- p.Article in journal (Refereed) Published
Abstract [en]

Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe-Cr-M (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have non-vanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of Fe-Cr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-31079 (URN)10.1063/1.3603024 (DOI)000292776500055 ()2-s2.0-79960548131 (ScopusID)
Note
Updated from submitted to published.Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2011-11-18Bibliographically approved
4. Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Open this publication in new window or tab >>Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Show others...
2011 (English)In: 2010 MRS Fall Meeting, 2011, 68-79 p.Conference paper (Refereed)
Abstract [en]

Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest sub-category of stainless steels having as the main building blocks the paramagnetic substitutional disordered Fe-Cr-Ni-based alloys. Because of that, austenitic steels represent the primary choice for non-magnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from first-principles theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact Muffin-Tin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Fe-based alloys.

Series
, Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1296
Keyword
magnetic properties, elastic properties, steel
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-31081 (URN)10.1557/opl.2011.1448 (DOI)2-s2.0-84859142705 (ScopusID)978-161839509-2 (ISBN)
Conference
2010 MRS Fall Meeting; Boston, MA
Note

QC 20110308

Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2014-09-04Bibliographically approved

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