| 1. |
- Gorbatov, O. I., et al.
(författare)
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Dependence of vacancy-solute interactions on magnetic state in dilute iron-based alloys
- 2011
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Ingår i: Solid-Solid Phase Transformations in Inorganic Materials. - Zurich-Durnten, Switzerland : TRANS TECH PUBLICATIONS. ; , s. 979-984
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Konferensbidrag (refereegranskat)abstract
- Vacancy-solute interactions play a crucial role in diffusion-controlled phase transformations, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. The knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) under irradiation, as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on density functional theory and employing the locally self-consistent Green’s function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Ti – Cu), and 4d (Nb – Ag) elements. Interactions within the first two coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a very strong effect on the vacancy-solute interactions.
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| 2. |
- Gorbatov, O. I., et al.
(författare)
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Vacancy-solute interactions in ferromagnetic and paramagnetic bcc iron : Ab initio calculations
- 2011
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 419:1-3, s. 248-255
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Tidskriftsartikel (refereegranskat)abstract
- Vacancy-solute interactions play a crucial role in diffusion-controlled processes, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. Detailed knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on the density functional theory and employing the locally self-consistent Green's function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Sc-Cu), and 4d (Y-Ag) elements. Unrelaxed interactions within the first three coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a strong effect on the vacancy-solute interactions. Implications of the obtained results for interpreting the effects of vacancy trapping and enhanced impurity diffusion are discussed.
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| 3. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Exploring monovalent copper compounds with oxygen and hydrogen
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:3, s. 686-689
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Tidskriftsartikel (refereegranskat)abstract
- New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu(2)O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal.
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| 4. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Thermodynamic properties of copper compounds with oxygen and hydrogen from first principles
- 2010
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Rapport (refereegranskat)abstract
- We employ quantum-mechanical calculations (based on density functional theory and linear response theory) in order to test the mechanical and chemical stability of several solid-state configurations of Cu1+, Cu2+, O2–, H1–, and H1+ ions. We begin our analysis with cuprous oxide (Cu2O, cuprite structure), cupric oxide (CuO, tenorite structure), and cuprous hydride (CuH, wurtzite and sphalerite structures) whose thermodynamic properties have been studied experimentally. In our calculations, all these compounds are found to be mechanically stable configurations. Their formation energies calculated at T = 0 K (including the energy of zero-point and thermal motion of the ions) and at room temperature are in good agreement with existing thermodynamic data. A search for other possible solid-state conformations of copper, hydrogen, and oxygen ions is then performed. Several candidate structures for solid phases of cuprous oxy-hydride (Cu4H2O) and cupric hydride (CuH2) have been considered but found to be dynamically unstable. Cuprous oxy-hydride is found to be energetically unstable with respect to decomposition onto cuprous oxide and cuprous hydride. Metastability of cuprous hydroxide (CuOH) is established in our calculations. The free energy of CuOH is calculated to be some 50 kJ/mol higher than the average of the free energies of Cu2O and water. Thus, cuprite Cu2O is the most stable of the examined Cu(I) compounds.
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| 5. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Thermodynamics of stable and metastable Cu-O-H compounds
- 2011
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Konferensbidrag (refereegranskat)abstract
- We apply density functional perturbation theory together with experimental studies in order to investigate the structure and physical properties of possible stable and metastable copper(I) compounds with oxygen and hydrogen. Copper(I) hydride, CuH, is found to be a metastable phase which decomposes at ambient conditions and exhibiting a semiconducting gap in the electronic spectrum. The calculated structure and phonon spectra are found to be in good agreement with experimental data. The phonon spectra of a novel metastable phase, copper(I) hydroxide, are also determined.
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| 6. |
- Razumovskiy, Vsevolod I., 1985-, et al.
(författare)
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Ab-initio calculations of kinetic properties in ZrC and TiC carbides
- 2011
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Konferensbidrag (refereegranskat)abstract
- Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).
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| 7. |
- Razumovskiy, Vsevolod I., 1985-, et al.
(författare)
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Effect of temperature on the elastic anisotropy of pure Fe and Fe0.9Cr0.1 random alloy
- 2011
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 107:20
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Tidskriftsartikel (refereegranskat)abstract
- The elastic properties of pure iron and substitutionally disordered 10 at. % Cr Fe-Cr alloy areinvestigated as a function of temperature using first-principles electronic-structure calculations bythe exact muffin-tin orbitals method. The temperature effects on the elastic properties are includedvia the electronic, magnetic, and lattice expansion contributions. We show that the degree ofmagnetic order in both pure iron and Fe90Cr10 alloy mainly determines the dramatic change of theelastic anisotropy of these materials at elevated temperatures. The effect of lattice expansion isfound to be secondary but also very important for quantitative modeling.
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| 8. |
- Razumovskiy, Vsevolod I., et al.
(författare)
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First-principles study of elastic properties of Cr- and Fe-rich Fe-Cr alloys
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:2
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Tidskriftsartikel (refereegranskat)abstract
- Elastic properties of substitutionally disordered Cr- and Fe-rich Fe-Cr alloys are derived from first-principles calculations using the exact muffin-tin orbitals method and the coherent potential approximation. A peculiarity in the concentration dependence of elastic constants in Fe-rich alloys is demonstrated and related to a change in the Fermi surface topology. Our calculations predict high values for the elastic constants of Cr-rich Fe-Cr alloys, but at the same time show that these alloys could be rather brittle according to the Pugh criterion (the ratio between shear and bulk moduli is calculated to be greater than 0.5).
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