| 1. |
- Isaev, Eyvas, et al.
(författare)
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Impact of lattice vibrations on equation of state of the hardest boron phase
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 83:13, s. 132106-
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Tidskriftsartikel (refereegranskat)abstract
- An accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.
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| 2. |
- Krasilnikov, O M, et al.
(författare)
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Elastic phase transitions in metals at high pressures
- 2012
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Ingår i: Journal of Physics. - : Institute of Physics. - 0953-8984 .- 1361-648X. ; 24:19, s. 195402-
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Tidskriftsartikel (refereegranskat)abstract
- The elastic phase transitions of cubic metals at high pressures are investigated within the framework of Landau theory. It is shown that at pressures comparable with the magnitude of the bulk modulus the phase transition is connected with the loss of stability relative to uniform deformation of the crystalline lattice. Discontinuity of the order parameter at the transition point and its equilibrium value are expressed through the second-to fourth-order elastic constants. The second-, third- and fourth-order elastic constants and phonon dispersion curves of vanadium under hydrostatic pressure are obtained by first-principles calculations. Structural transformation in vanadium under pressure is studied using the obtained results. It is shown that the experimentally observed at P approximate to 69 GPa phase transition in vanadium is the first-order phase transition close to a second-order phase transition.
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| 3. |
- Krasilnikov, O M, et al.
(författare)
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Elastic properties, lattice dynamics and structural transitions in molybdenum at high pressures
- 2014
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 81, s. 313-318
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Tidskriftsartikel (refereegranskat)abstract
- The structural phase transitions in molybdenum under pressures are investigated on the basis of first principle analysis of elastic constants behavior and phonon dispersions. The definition of the effective elastic constants of nth order ( nP2), governing the elastic properties of a loaded crystal, is given. The effective elastic constants of second and third order and the phonon dispersions are calculated by DFT methods in the pressure range of P = 0 - 1400 GPa, T = 0 K. The calculation results at P = 0 are in good agreement with the available experimental data. On the basis of the obtained results the stability of the bcc phase of molybdenum under pressure and the possibility of the phase transition are investigated. It is shown that the effective elastic constant eC0 which corresponds to the tetragonal uniform strain of a loaded crystal undergoes significant softening at P andgt; 400 GPa. In the same pressure range the frequencies of the transverse branch T-[110](-) [zeta zeta 0] also begin to soften and already at P approximate to 1000 GPa they become imaginary near the wave vector [1/4 1/4 0]. The bcc -andgt; dhcp phase transition associated with the softening of eC0 and the soft mode T-[110](-)[1/4 1/4 0] is discussed.
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| 4. |
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| 5. |
- 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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| 6. |
- Belov, Maxim, et al.
(författare)
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Hydrogen in palladium: Anharmonicity of lattice dynamics from first principles
- 2015
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Ingår i: Physics of the solid state. - : M A I K Nauka - Interperiodica. - 1063-7834 .- 1090-6460. ; 57:2, s. 260-265
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Tidskriftsartikel (refereegranskat)abstract
- The interaction potentials of the palladium and hydrogen sublattices at different hydrogen concentrations have been obtained in terms of the density functional theory and ab initio pseudopotentials. It has been shown that the anharmonicity of this interaction depends on the hydrogen concentration. The phonon spectrum of palladium hydride PdH has been calculated in the harmonic approximation and taking into account the anharmonic effects. The temperature-dependent effective potential technique accounting for the anharmonic effects of lattice vibrations has been described.
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| 7. |
- Belov, M P, et al.
(författare)
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Ab initio lattice dynamics of CoH and NiH
- 2011
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 509, s. S857-S859
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Tidskriftsartikel (refereegranskat)abstract
- Ground state parameters and lattice dynamics of CoH and NiH phases are studied by means of the state-of-the-art ab initio pseudopotentials methods. Calculated ground state parameters and phonon DOS are in rather good agreement with available experimental data. No phase transformation for CoH and NiH was found in a wide pressure and temperature range.
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| 8. |
- Belov, M P, et al.
(författare)
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Hydrogen in the approximant i-TiZrHf: The energy state, charge, and diffusion
- 2010
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Ingår i: PHYSICS OF THE SOLID STATE. - : Springer Science Business Media. - 1063-7834. ; 52:6, s. 1111-1114
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Tidskriftsartikel (refereegranskat)abstract
- The energy of hydrogen dissolution in different tetrahedral pores of a 1/1 approximant of the icosahedral TiZrHf quasicrystal has been determined in terms of the density functional theory and ab initio pseudopotentials. At low and high degrees of loading of TiZrHf with hydrogen, the charges of atoms involved in the system and the Mayer bond order have been calculated for all possible M-M and M-H pairs. The diffusion coefficient of a single hydrogen atom in the system under study has been estimated numerically.
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| 9. |
- Bleskov, I D, et al.
(författare)
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Electronic structure and ground state parameters of Ru1-x Me (x) Al refractory alloys
- 2010
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Ingår i: PHYSICS OF THE SOLID STATE. - : Springer Science Business Media. - 1063-7834. ; 52:9, s. 1803-1809
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and ground state parameters of B2 RuAl-based refractory alloys have been investigated in the framework of the density functional theory using the exact muffin-tin orbital method in combination with the coherent potential approximation. It has been demonstrated that the number of states at the Fermi level for the Ru1 - x Me (x) Al alloys as a function of the alloying metal content has a minimum, which indicates a change in the Fermi surface topology and the presence of specific features in the behavior of elastic constants. It has been concluded that the electronic structure of the alloys can be described in terms of the rigid band model. The nonlinear variations of the lattice parameters of the alloys has been explained.
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| 10. |
- 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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| 11. |
- Isaev, Eyvaz, et al.
(författare)
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Intrinsic defects and transition metal impurities in GaAs
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 272:3, s. 1961-1962
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamics of intrinsic point defects, 3d-transition metal (TM) impurities, and various defect pairs in GaAs have been studied by means of the locally self-consistent Green's function method. Antisite defects, As-Ga, are found to be the most energetically favorable defects in the As-rich GaAs. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The magnetic moments of TM impurities in the GaAs host are calculated under the assumption that orbital moments of TM are quenched and the total magnetization is due to spill ordering of electrons in the crystal. Thermodynamic possibility of formation of complexes between TM-atoms is investigated.
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| 12. |
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| 13. |
- Krasilnikov, O. M., et al.
(författare)
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Comment on "Nonlinear elasticity of prestressed single crystals at high pressure and various elastic moduli"
- 2022
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 105:22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We show that elastic moduli of higher (third and fourth) order of prestressed single crystals at high pressure, obtained from the Gibbs free energy, enter the relation between the Cauchy stress and Lagrange finite-strain tensor the same way they do for the second-order elastic moduli and, therefore, directly describe the nonlinear elasticity of prestressed crystals.
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| 14. |
- Krasilnikov, O. M., et al.
(författare)
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Nonlinear elasticity of epsilon -Fe: The pressure effect
- 2019
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:18
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Tidskriftsartikel (refereegranskat)abstract
- Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Gruneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Gruneisen parameters for the high-symmetry directions. The latter are directly compared with the Gruneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.
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| 15. |
- Mosyagin, Igor, et al.
(författare)
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Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach
- 2017
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Ingår i: Computer Physics Communications. - : ELSEVIER SCIENCE BV. - 0010-4655 .- 1879-2944. ; 220, s. 20-30
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Tidskriftsartikel (refereegranskat)abstract
- We present a description of a technique for ab initio calculations of the pressure dependence of second and third-order elastic constants. The technique is based on an evaluation of the corresponding Lagrangian stress tensor derivative of the total energy assuming finite size of the deformations. Important details and parameters of the calculations are highlighted. Considering body-centered cubic Mo as a model system, we demonstrate that the technique is highly customizable and can be used to investigate non-linear elastic properties under high-pressure conditions. (C) 2017 Elsevier B.V. All rights reserved.
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| 16. |
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| 17. |
- Ponomareva, A V, et al.
(författare)
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Effect of Re content on elastic properties of B2 NiAl from ab initio calculations
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 586, s. S274-S278
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Tidskriftsartikel (refereegranskat)abstract
- The effect of substitutional alloying of Re on elastic properties of B2 NiAl has been studied using first-principles electronic-structure calculations by the exact muffin-tin orbitals method and the coherent potential approximation. Our calculations have shown that elastic constants C-12, C-44 and bulk modulus B of (Ni1-xRex) Al alloys increase with Re composition almost linearly, but concentration dependence of elastic constants C-11, Young modulus E, shear modulus G, G/B ratio and the Cauchy pressure P-C is strongly nonmonotonously and has peculiarities near the concentration x = 30 at.% Re. Analyzing the density of states and Fermi surface sections we have a direct connection between the behavior of the elastic constants of (Ni1-xRex) Al alloys and changes in the interatomic bonding and Fermi surface topology.
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| 18. |
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| 19. |
- Ponomareva, A V, et al.
(författare)
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Site preference and effect of alloying on elastic properties of ternary B2 NiAl-based alloys
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:14, s. 144117-
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Tidskriftsartikel (refereegranskat)abstract
- Using the exact muffin-tin orbitals method in conjunction with the coherent potential approximation, we study the site preference of transition metal impurities X (X = Sc, Ti, V, Cr, W, Re, Co) in B2 NiAl and their effect on its elastic properties. Analyzing interatomic bonding of NiAl-X alloys and elastic characteristics evaluated from the elastic constants C-11, C-12, and C-44, we predict that the addition of W, V, Ti, and Re atoms could yield improved ductility for B2 NiAl-X alloys without significant changes in the macroscopic elastic moduli.
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| 20. |
- Ponomareva, A. V., et al.
(författare)
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Surface segregation energy in bcc Fe-rich Fe-Cr alloys
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:24, s. 5406-
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Tidskriftsartikel (refereegranskat)abstract
- The exact muffin-tin orbitals (EMTO) technique in conjunction with the coherent-potential approximation (CPA) as well as the projector-augmented-wave (PAW) method have been used to calculate the surface segregation energy of Cr at the (100) surface of Fe-rich bcc Fe-Cr alloys. We find that PAW results strongly depend on the supercell size used in the calculations. In particular, for large supercells, the surface segregation energy of Cr is positive, which means that Cr should not segregate toward the surface of diluted alloys. This is in agreement with our EMTO-CPA results as well as previous surface Green's-function calculations. However, the surface segregation energy of Cr is negative if small unit cells are used for simulations. This is in agreement with previous full-potential supercell calculations. We explain such a size dependence by a peculiar concentration dependence of interatomic interactions in ferromagnetic Fe-Cr alloys.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Razumovskiy, Vsevolod I., 1985-, et al.
(författare)
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Effect of Alloying Elements and Impurities on Interface properties in Aluminum Alloys
- 2011
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Ingår i: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 53:11, s. 2189-2193
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Tidskriftsartikel (refereegranskat)abstract
- The segregation energies of B, Si, P, Cr, Ni, Zr, and Mg on the special grain boundary (GB) Σ5 (210)[100] and on the open (210) surface of aluminum have been determined and the GB splitting energy has been calculated by the density functional theory methods. It has been shown that all elements listed above enrich the GB; for B, Si, P, Cr, Ni and Zr, Mg, interstitial and substitutional sites are preferred, respectively. The effect of alloying elements on the GB binding has been estimated using the parameter η equal to the change in the fracture work of the aluminum GB when adding alloying element atoms. From the viewpoint of strengthening the GB binding forces, Zr, Cr, Ni, and Mg are efficient, Si and B are neutral and phosphorus weakens GBs.
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| 26. |
- Razumovskiy, Vsevolod I., et al.
(författare)
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The effect of alloying elements on grain boundary and bulk cohesion in aluminum alloys : An ab initio study
- 2011
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 65:10, s. 926-929
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Tidskriftsartikel (refereegranskat)abstract
- The effect of B, Si, P, Cr, Ni, Zr and Mg impurities on cohesive properties of Al and its special grain boundary (GB) Sigma 5 (2 1 0) [1 0 0], as well as their segregation behavior at the GB and (2 1 0) surface are studied from first principles. Our analysis determines Ni to be the best and P the worst alloying elements in regard to the overall resistance to decohesion of Al alloys.
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| 27. |
- Razumovskiy, Vsevolod I., 1985-, et al.
(författare)
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The influence of alloying elements on grain boundary and bulk cohesion in aluminum all : Ab initio study
- 2012
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Ingår i: Thermec 2011 Supplement. - : Trans Tech Publications Inc.. - 9783037853047 ; , s. 417-422
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Konferensbidrag (refereegranskat)abstract
- The effect of B, Si, P, Cr, Ni, Zr and Mg on cohesive properties of Al and the specialgrain boundary (GB) Σ5 (210)[100], as well as their segregation behavior at the GB and the (210)surface are studied by first principles method. The analysis of these parameters allows us to singleout Ni as the best and phosphorus as the worst interatomic bond strengthening alloying elements.
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