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Describing interstitials in close-packed lattices: first-principles study
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
2010 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology , 2010. , s. 32
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-31124ISBN: 978-91-7415-880-9 (tryckt)OAI: oai:DiVA.org:kth-31124DiVA, id: diva2:402781
Presentation
2011-03-25, Konferensrummet, Materialvetenskap, KTH, Brinellvägen 23, Stockholm, 10:00
Merknad
QC 20110309Tilgjengelig fra: 2011-03-09 Laget: 2011-03-09 Sist oppdatert: 2011-03-09bibliografisk kontrollert
Delarbeid
1. Completeness of the exact muffin-tin orbitals: application to hydrogenated alloys
Åpne denne publikasjonen i ny fane eller vindu >>Completeness of the exact muffin-tin orbitals: application to hydrogenated alloys
2010 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 4Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
total-energy calculations, initio molecular-dynamics, wave basis-set, ab-initio, electron-gas, surface-energy, ground-state, metals, approximation, semiconductors
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-19159 (URN)10.1103/PhysRevB.81.045122 (DOI)000274002500053 ()2-s2.0-77954824021 (Scopus ID)
Forskningsfinansiär
Swedish Research Council
Merknad

QC 20110121

Tilgjengelig fra: 2010-08-05 Laget: 2010-08-05 Sist oppdatert: 2017-12-12bibliografisk kontrollert
2. Influence of Magnesium on hydrogenated ScAl1-xMgx alloys: a theoretical study
Åpne denne publikasjonen i ny fane eller vindu >>Influence of Magnesium on hydrogenated ScAl1-xMgx alloys: a theoretical study
2011 (engelsk)Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 50, nr 10, s. 2848-2853Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
Hydrides, Sc-based alloys, Hydrogen storage materials, First-principles calculations
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-31070 (URN)10.1016/j.commatsci.2011.04.040 (DOI)000293486900011 ()2-s2.0-79959506804 (Scopus ID)
Forskningsfinansiär
Swedish Research CouncilEU, European Research Council
Merknad

QC 20161216

Tilgjengelig fra: 2011-03-08 Laget: 2011-03-08 Sist oppdatert: 2017-12-11bibliografisk kontrollert
3. The bain path of paramagnetic Fe-Cr based alloys
Åpne denne publikasjonen i ny fane eller vindu >>The bain path of paramagnetic Fe-Cr based alloys
2011 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, nr 1, s. 013708-Artikkel i tidsskrift (Fagfellevurdert) 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.

HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-31079 (URN)10.1063/1.3603024 (DOI)000292776500055 ()2-s2.0-79960548131 (Scopus ID)
Merknad
Updated from submitted to published.Tilgjengelig fra: 2011-03-08 Laget: 2011-03-08 Sist oppdatert: 2017-12-11bibliografisk kontrollert
4. Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Åpne denne publikasjonen i ny fane eller vindu >>Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Vise andre…
2011 (engelsk)Inngår i: 2010 MRS Fall Meeting, 2011, s. 68-79Konferansepaper, Publicerat paper (Fagfellevurdert)
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.

Serie
Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1296
Emneord
magnetic properties, elastic properties, steel
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-31081 (URN)10.1557/opl.2011.1448 (DOI)2-s2.0-84859142705 (Scopus ID)978-161839509-2 (ISBN)
Konferanse
2010 MRS Fall Meeting; Boston, MA
Merknad

QC 20110308

Tilgjengelig fra: 2011-03-08 Laget: 2011-03-08 Sist oppdatert: 2014-09-04bibliografisk kontrollert

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