| 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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