| 1. |
- Andersson, David A., et al.
(författare)
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First-principles based calculation of binary and multicomponent phase diagrams for titanium carbonitride
- 2008
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Ingår i: Calphad. - : Elsevier BV. - 0364-5916 .- 1873-2984. ; 32:3, s. 543-565
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Forskningsöversikt (refereegranskat)abstract
- In this paper we have used a combined first principles and Calphad approach to calculate phase diagrams in the titanium-carbon-nitrogen system, with particular focus on the vacancy-induced ordering of the substoichiometric carbonitride phase, TiCxNy (x + y <= 1). Results from earlier Monte Carlo simulations of the low-temperature binary phase diagrams are used in order to formulate sublattice models for TiCxNy within the compound energy formalism (CEF) that are capable of describing both the low temperature ordered and the high-temperature disordered state. We parameterize these models using first-principles calculations and then we demonstrate how they can be merged with thermodynamic descriptions of the remaining Ti-C-N phases that are derived within the Calphad method by fitting model parameters to experimental data. We also discuss structural and electronic properties of the ordered end-member compounds, as well as short range order effects in the TiCxNy phase.
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| 2. |
- Arapan, Sergiu, et al.
(författare)
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Effect of the boundary roughness on the conductance of double quantum wire in a magnetic field
- 2003
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Ingår i: EUROPHYSICS LETTERS. ; 64, s. 239-245
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Forskningsöversikt (populärvet., debatt m.m.)abstract
- We investigate the effect of the boundary roughness scattering on the conductance of a disordered tunnel-coupled quantum wire in the presence of a magnetic field. It is shown that the average distance between the neighboring discontinuities of the boundary profile plays an important role in the transport properties of the system and the manifestation of the localization-delocalization effect. Present studies point out a new effect consisting in thedecrease of the conductance with the increase of the disorder correlation length.
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| 3. |
- Isaev, E. I., et al.
(författare)
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Phonon related properties of transition metals, their carbides, and nitrides : A first-principles study
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:12
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Forskningsöversikt (refereegranskat)abstract
- Lattice dynamics of body-centered cubic (bcc) V-b-VIb group transition metals (TM), and B1-type monocarbides and mononitrides of IIIb-VIb transition metals are studied by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Ground state parameters of transition metals and their compounds are correctly reproduced with the generated ultrasoft pseudopotentials. The calculated phonon spectra of the bcc metals are in excellent agreement with results of inelastic neutron scattering experiments. We show that the superconductivity of transition metal carbides (TMC) and transition metal nitrides (TMN) is related to peculiarities of the phonon spectra, and the anomalies of the spectra are connected to the number of valence electrons in crystals. The calculated electron-phonon interaction constants for TM, TMC, and TMN are in excellent agreement with experimentally determined values. Phonon spectra for a number of monocarbides and mononitrides of transition metals within the cubic NaCl- and hexagonal WC-type structures are predicted. Ideal stoichiometric B1 crystals of ScC, YC, and VC are predicted to be dynamically stable and superconducting materials. We also conclude that YN is a semiconductor.
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| 4. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Electronic structure and effective chemical and magnetic exchange interactions in bcc Fe-Cr alloys
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:5, s. 054202-
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Forskningsöversikt (refereegranskat)abstract
- Electronic structure calculations are employed in order to investigate the cohesive properties (lattice parameter, enthalpy of formation, and bulk modulus) of random Fe-Cr alloys as a function of composition and magnetic state, as well as to derive the chemical and magnetic exchange interactions of the constituent atoms. The calculations predict certain anomalies in the cohesive properties of ferromagnetic alloys at a concentration of about 7 at % Cr; these anomalies may be related to the changes in Fermi-surface topology that occur with composition in this alloy system. The obtained interatomic interactions are used as parameters in the configurational (Ising) and magnetic (Heisenberg) Hamiltonians for modeling finite-temperature thermodynamic properties of the alloys. We discuss the approximations and limitations of similar modeling approaches, investigate the origin of existing difficulties, and analyze possible ways of extending the theoretical models in order to capture the essential physics of interatomic interactions in the Fe-Cr or similar alloys where magnetism plays a crucial role in the phase stability.
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| 5. |
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| 6. |
- Vitos, Levente, et al.
(författare)
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Modeling of alloy steels
- 2002
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Ingår i: Materials Today. - 1369-7021. ; 5:10, s. 14-23
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Forskningsöversikt (refereegranskat)abstract
- The use of computational quantum mechanics for the theoretical modeling of material properties of steel was described. Steel properties depend on the microstructure formed during the manufacturing process as well as on the concentartion and distribution of alloying elements and impurities. The computational methods allows reserachers to separate the effect of alloying elements on physical and chemical properties and to map the compositional distribution into the property distribution with arbitrary accuracy. The computational material design approach based on quantum theory with thermodynamics constitutes a profound advance in the design process of industrially relevant materials.
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