| 1. |
- Delczeg, Lorand, et al.
(författare)
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Assessing common density functional approximations for the ab initio description of monovacancies in metals
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:20
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Tidskriftsartikel (refereegranskat)abstract
- Using the exact muffin-tin orbitals method, we investigate the accuracy of five common density functional approximations for the theoretical description of the formation energy of monovacancies in three close-packed metals. Besides the local density approximation (LDA), we consider two generalized gradient approximation developed by Perdew and co-workers (PBE and PBEsol) and two gradient-level functionals obtained within the subsystem functional approach (AM05 and LAG). As test cases, we select aluminum, nickel, and copper, all of them adopting the face centered cubic crystallographic structure. Our results show that, compared to the recommended experimental values, LDA is be the most reliable approximation for the vacancy formation energies in these metals. However, taking into account also the performances of the functionals for the equation of state changes the final verdict in favor of the generalized gradient approximations.
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| 2. |
- Punkkinen, Marko Patrick John, et al.
(författare)
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Adhesion of the iron-chromium oxide interface from first-principles theory
- 2013
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:49, s. 495501-
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Tidskriftsartikel (refereegranskat)abstract
- We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.
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| 3. |
- Delczeg-Czirjak, Erna Krisztina, 1978-, et al.
(författare)
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Ab initio study of the elastic anomalies in Pd-Ag alloys
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio total-energy calculations, based on the exact muffin-tin orbital method, are used to determine the elastic properties of Pd1-xAgx random alloys in the face-centered-cubic crystallographic phase. The compositional disorder is treated within the coherent-potential approximation. The single crystal and polycrystalline elastic constants and the Debye temperature are calculated for the whole range of concentration, 0 <= x <= 1. It is shown that the variation in the elastic parameters of Pd-Ag alloys with chemical composition strongly deviates from a simple linear or parabolic trend. The complex electronic origin of these anomalies is demonstrated.
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| 4. |
- Delczeg-Czirjak, Erna K., et al.
(författare)
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Monovacancy formation energies and Fermi surface topological transitions in Pd-Ag alloys
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:22
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Tidskriftsartikel (refereegranskat)abstract
- Using first-principles mean-field alloy theory, we calculate the vacancy formation energies of the face-centered-cubic Pd-Ag alloys as a function of chemical composition. The effect of Fermi surface topological transition on the composition dependence of the vacancy formation energies is detectable and is consistent with what has previously been shown for the bulk properties of Pd1-xAgx.
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| 5. |
- Gercsi, Z., et al.
(författare)
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Magnetoelastic effects in doped Fe2P
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:2, s. 024417-
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Tidskriftsartikel (refereegranskat)abstract
- We use combined high resolution neutron diffraction (HRPD) with density functional theory (DFT) to investigate the exchange striction at the Curie temperature (T-C) of Fe2P and to examine the effect of boron and carbon doping on the P site. We find a significant contraction of the basal plane on heating through T-C with a simultaneous increase of the c axis that results in a small overall volume change of similar to 0.01%. At the magnetic transition the Fe-I-Fe-I distance drops significantly and becomes shorter than Fe-I-Fe-II. The shortest metal-metalloid (Fe-I-P-I) distance also decreases sharply. Our DFT model reveals the importance of the latter as this structural change causes a redistribution of the Fe I moment along the c axis (Fe-P chain). We are able to understand the site preference of the dopants, the effect of which can be linked to the increased moment on the Fe-I site, brought about by strong magnetoelasticity and changes in the electronic band structure.
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| 6. |
- Punkkinen, M. P. J., et al.
(författare)
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Does Bi form clusters in GaAs1-xBix alloys?
- 2014
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 29:11, s. 115007-
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Tidskriftsartikel (refereegranskat)abstract
- GaAs1 - xBix alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 - xBix with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 - xBix film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.
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| 7. |
- Arora, Monika, et al.
(författare)
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Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys
- 2021
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetic damping properties of polycrystalline Fe-V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%-20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53 +/- 0.08) x 10-3, which is approximately a factor of 3 higher than our calculated value of 0.48 x 10-3. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.
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| 8. |
- Cedervall, J., et al.
(författare)
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Magnetic and mechanical effects of Mn substitutions in AlFe 2 B 2
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 482, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe 2 B 2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe 2 B 2 . The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe 2 B 2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB 2 . Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe 2 B 2 . The Mn-Mn exchange interactions in AlMn 2 B 2 are found to be very small.
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| 9. |
- Cedervall, Johan, et al.
(författare)
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Magnetic structure of the magnetocaloric compound AlFe2B2
- 2016
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 664, s. 784-791
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic a-axis. The magnetic entropy change from 0 to 800 kA/m was found to be - 1.3 J/K kg at the magnetic transition temperature.
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| 10. |
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