| 11. |
- Golosova, N. O., et al.
(författare)
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Magnetic and structural properties of FeCO3 at high pressures
- 2017
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:13
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Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of siderite FeCO3 have been studied by means of neutron powder diffraction at pressures up to 7.5 GPa and first-principles theoretical calculations. The lattice compression in the rhombohedral calcite-type structure is dominated by the reduction of the Fe-O bonds, while the changes of the C-O bonds are much less pronounced. The Neel temperature of the antiferromagnetic ( AFM) ground state increases substantially under pressure with a coefficient dT(N)/dP = 1.8K/GPa, which is about 1.5 times larger in comparison with those predicted by the empirical Bloch rule. The ab initio calculations were performed in the framework of the density functional theory including Hubbard-U correction. The calculated structural parameters and Neel temperature as functions of pressure provide a reasonable agreement with the experimental results. The analysis of the density of electronic states points toward increased covalent bonding between the Fe and O atoms upon pressure, giving rise to unexpectedly large pressure coefficient of the Neel temperature and reduced ordered magnetic moments of Fe atoms.
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| 12. |
- Mukhamedov, B. O., et al.
(författare)
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Thermodynamic and physical properties of Zr3Fe and ZrFe2 intermetallic compounds
- 2019
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Ingår i: Intermetallics (Barking). - : ELSEVIER SCI LTD. - 0966-9795 .- 1879-0216. ; 109, s. 189-196
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Tidskriftsartikel (refereegranskat)abstract
- Experimental differential scanning calorimetry measurements and ab-initio simulations were carried out to define the heat capacities of Zr3Fe and C15-ZrFe2 compounds from 0 K up to their maximum stability temperatures. Experimental measurements of heat capacity of each compound were performed for the first time in wide range of temperatures. Density functional theory and quasi-harmonic approximation (QHA) were employed to calculate the free energy of the studied systems as a function of volume and temperature. A good agreement was observed between theoretical and experimental heat capacities within validity range of the QHA. This makes it possible to combine theoretical and experimental data to determine the standard entropies of intermetallic compounds.
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| 13. |
- Ponomareva, A. V., et al.
(författare)
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Effect of pressure on phase stability in 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. ; 84:9, s. 094422-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of hydrostatic pressure on the phase stability of Fe-Cr alloys has been studied using ab initio methods. We show that while pressure decreases the tendency toward the phase separation in the paramagnetic state of bcc alloys, in the ferromagnetic state it reduces the alloy stability at low Cr concentration and vice versa, makes the solid solution more stable at higher concentrations. This behavior of the phase stability can be predicted from the deviation of the lattice parameter from Vegard's law in bcc Fe-Cr alloys. On the atomic level, the pressure effect can be explained by the suppression of the local magnetic moments on Cr atoms, which gives rise to a decrease of the Fe-Cr magnetic exchange interaction at the first coordination shell and, as a result, to the observed variation of the ordering tendency between the Fe and Cr atoms.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Abrikosov, I. A., et al.
(författare)
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Correlation between electronic structure, magnetism and physical properties of Fe-Cr alloys : Ab initio modeling
- 2008
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Ingår i: MATERIALS ISSUES FOR GENERATION IV SYSTEMS. - Dordrecht : Springer Netherlands. ; , s. 153-168
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Konferensbidrag (refereegranskat)abstract
- We review recent developments in the field of ab initio electronic structure theory and its application for studies of phase stability of alloy systems. Basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of intermetallic compounds and alloys based on the density functional theory are outlined. We concentrate on methods that allow for an efficient treatment of disorder effects, and illustrate their predictive power for the case of Fe-Cr system. We show that in the ferromagnetic alloys there are peculiarities of the mixing enthalpy in the low-Cr region in the bee phase. Thus the stability of the Cr containing steels stems from the negative mixing enthalpy at low concentrations of chromium. We explain the effect by the strong concentration dependence of the interatomic interactions in Fe-Cr system.
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| 19. |
- Abrikosov, Igor, et al.
(författare)
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Recent progress in simulations of the paramagnetic state of magnetic materials
- 2016
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Ingår i: Current opinion in solid state & materials science. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-0286 .- 1879-0348. ; 20:2, s. 85-106
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Forskningsöversikt (refereegranskat)abstract
- We review recent developments in the field of first-principles simulations of magnetic materials above the magnetic order disorder transition temperature, focusing mainly on 3d-transition metals, their alloys and compounds. We review theoretical tools, which allow for a description of a system with local moments, which survive, but become disordered in the paramagnetic state, focusing on their advantages and limitations. We discuss applications of these theories for calculations of thermodynamic and mechanical properties of paramagnetic materials. The presented examples include, among others, simulations of phase stability of Fe, Fe-Cr and Fe-Mn alloys, formation energies of vacancies, substitutional and interstitial impurities, as well as their interactions in Fe, calculations of equations of state and elastic moduli for 3d-transition metal alloys and compounds, like CrN and steels. The examples underline the need for a proper treatment of magnetic disorder in these systems. (C) 2015 Elsevier Ltd. All rights reserved.
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| 20. |
- Barannikova, S A, et al.
(författare)
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Significant correlation between macroscopic and microscopic parameters for the description of localized plastic flow auto-waves in deforming alloys
- 2012
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Ingår i: Solid State Communications. - : Elsevier. - 0038-1098 .- 1879-2766. ; 152:9, s. 784-787
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of mechanical properties of materials and a possibility to predicting them from ab initio calculations have fundamental importance for solid state theory. In this work we establish a significant correlation between the product of the macroscopic parameters of localized plastic flow auto-waves in deforming alloys, their length and propagation rate and the product of the microscopic (lattice) parameters of these materials, the spacing between close-packed planes of the lattice and the rate of transverse elastic waves. Thus, these products can be regard as invariants of plastic and elastic deformation processes, respectively. Moreover, the established regularity suggests that the elastic and the plastic processes simultaneously involved in the deformation are closely related. Our work also demonstrates that ab initio simulations can be used for the prediction of parameters of localized plastic flow auto-waves in deforming alloys.
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