| 1. |
- Smirnova, E. A., et al.
(författare)
-
Effect of band filling on the pressure-induced structural transition in Mo-Re alloys
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed investigation of the combined effect of alloying and compression on the structural stability of random bcc and hcp alloys in the Mo-Re system. We use the linear-muffin-tin-orbital Green's-function method within the coherent potential approximation (LMTO-GF-CPA) and the full-potential linear-muffin-tin-orbital (FP-LMTO) method. For pure Mo we find a bcc to hcp transition pressure to take place at 620 GPa (FP-LMTO) or 730 GPa Mbar (LMTO-GF-CPA). The calculated equation of states for Mo68Re32 alloy is in good agreement with the experimental data, and the calculated bcc-hcp transition pressure is above 400 GPa. This number is much higher than the one anticipated in earlier model calculations. The agreement between the model calculations, ab initio calculations, and the experiment is restored when self-consistent occupation numbers of sp and d electrons are used.
|
|
| 2. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
-
Constitutional and thermal point defects in B2 NiAl
- 2000
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:9, s. 6003-6018
-
Tidskriftsartikel (refereegranskat)abstract
- The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects (antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively) are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.
|
|
| 3. |
- Baykov, Vitaly, et al.
(författare)
-
Ab Initio Studies of the Energy Characteristics and Magnetic Properties of Point Defects in GaAs
- 2005
-
Ingår i: Physics of the solid state. - : Pleiades Publishing Ltd. - 1063-7834 .- 1090-6460. ; 47:10, s. 1831-1836
-
Tidskriftsartikel (refereegranskat)abstract
- The formation energies of intrinsic point defects and solution energies of transition metal impurities in gallium arsenide are determined on the basis of ab initio calculations using the method of a locally self-consistent Green's function, which is a generalization of the coherent potential approximation. Based on the calculated energies, the conclusion is made that the As-Ga antisite defect is the most common intrinsic defect in GaAs. Calculations showed that transition metal impurities, except for Ni, preferentially occupy gallium sites substitutionally. The magnetic moments of impurity atoms are calculated as a function of the chemical environment. It is shown that, in compensated GaAs, Mn atoms tend to form clusters.
|
|
| 4. |
- Bleskov, I. D., et al.
(författare)
-
Ab initio calculations of elastic properties of Ru1-xNixAl superalloys
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:16
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio total energy calculations based on the exact muffin-tin orbitals method, combined with the coherent potential approximation, have been used to study the thermodynamical and elastic properties of substitutional refractory Ru1-xNixAl alloys. We have found that the elastic constants C' and C11 exhibit pronounced peculiarities near the concentration of about 40 at. % Ni, which we ascribe to electronic topological transitions. Our suggestion is supported by the Fermi surface calculations in the whole concentration range. Results of our calculations show that one can design Ru-Ni-Al alloys substituting Ru by Ni (up to 40 at. %) with almost invariable elastic constants and reduced density.
|
|
| 5. |
|
|
| 6. |
- Isaev, E. I., et al.
(författare)
-
Dynamical stability of Fe-H in the Earth's mantle and core regions
- 2007
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 104:22, s. 9168-9171
-
Tidskriftsartikel (refereegranskat)abstract
- The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp -> hcp -> fcc sequence of structural transitions.
|
|
| 7. |
|
|
| 8. |
- Isaeva, E. I., et al.
(författare)
-
Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
- 2004
-
Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 129:12, s. 809-814
-
Tidskriftsartikel (refereegranskat)abstract
- The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.
|
|
| 9. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
-
Defect-induced magnetic structure in (Ga1-xMnx)As
- 2002
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88:18, s. 187202-
-
Tidskriftsartikel (refereegranskat)abstract
- We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga1-xMnx)As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga1-xMnx)As . We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.
|
|
| 10. |
- Ponomareva, A., et al.
(författare)
-
Ab initio investigations of surface magnetism in V-Mo
- 2004
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 272-276, s. 1198-1200
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic properties of the (0 0 1) surface of pure vanadium and disordered binary Mo-V alloys have been investigated from the first-principles by means of the LMTO-GF-CPA technique, the fixed spin moment method, and the direct exchange Monte-Carlo statistical mechanics simulations. The binary alloys, as well as pure constituent metals, are nonmagnetic in the bulk. However, we have shown that the (1 0 0) surface of uniformly random and segregated Mo-V alloys is magnetic. The magnetism of the V monolayer on the Mo(0 0 1) surface has also been studied. In particular, the surface relaxation effect has resulted in a reduction of the magnetic moments for V atoms, but the surface magnetism is still present in the system. Including of semi-core states as valence ones does not alter this conclusion.
|
|
