| 1. |
- Alling, Björn, et al.
(författare)
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Metastability of fcc-related Si-N phases
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:13, s. 132103-132103
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of superhardening in TiN/SiNx nanocomposites and the prediction of extreme hardness in bulk gamma-Si3N4 have attracted a large interest to this material system. Attempts to explain the experimental findings by means of first-principles calculations have so far been limited to static calculations. The dynamical stability of suggested structures of the SiNx tissue phase critical for the understanding of the nanocomposites is thus unknown. Here, we present a theoretical study of the phonon-dispersion relations of B1 and B3 SiN. We show that both phases previously considered as metastable are dynamically unstable. Instead, two pseudo-B3 Si3N4 phases derived from a L1(2)- or D0(22)-type distribution of Si vacancies are dynamically stable and might explain recent experimental findings of epitaxial SiNx in TiN/SiNx multilayers.
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Bleskov, I. D., et al.
(författare)
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Ab initio calculations of elastic properties of Ru1-xNixAl superalloys
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:16
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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.
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| 6. |
- 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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| 7. |
- Bleskov, Ivan, et al.
(författare)
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Elastic constants of Ru100-xMexAl refractory alloys
- 2011
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Ingår i: SOLID STATE COMMUNICATIONS. - : Elsevier Science B.V., Amsterdam.. - 0038-1098. ; 151:3, s. 242-244
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Tidskriftsartikel (refereegranskat)abstract
- Elastic constants of disordered refractory Ru100-xMexAl alloys are calculated from first principles using a density-functional-theory based exact muffin-tin orbitals method combined with a coherent potential approximation. As alloying elements we considered Me = Ni, Co, Ir and Fe. We have found that peculiarities in the concentration dependencies of elastic constants on alloying metals content depend on their position in the Periodic Table with respect to Ru. These peculiarities can be connected with the changes in the electronic structure which take place upon alloying.
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| 8. |
- Isaev, Eyvas, et al.
(författare)
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Ab initio Calculations of Elastic Constants of Superalloys
- 2011
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Ingår i: JAPANESE JOURNAL OF APPLIED PHYSICS. - : Japan Society of Applied Physics / Japanese Journal of Applied Physics; 1999. - 0021-4922. ; 50:5
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Tidskriftsartikel (refereegranskat)abstract
- Using the-state-of-the-art ab initio method we have studied elastic constants of alloys potentially interesting for high temperature applications. We have shown that Cr substitutes the Al sublattice in B2 NiAl at concentration up to 40 at. %, but at higher Cr content it prefers the Ni-sublattice. Alloying of NiAl with Cr yields reduced strength but improves the ductility of the alloys. Alloying of NiAl with W which substitutes the Al sublattice, leads to a strong decrease of the shear modulus, and near 50 at.% of W the alloy becomes mechanically unstable as elastic constant C is negative. This is in agreement with our phonon calculations where we found soft modes along the [110] direction for B2 NiW. According to our calculations in (Ru,Ni)Al alloys the shear modulus is almost constant up to 40 at.% of Ni, at higher Ni concentrations it is drastically reduced. We have shown that the changes in elastic properties of (Ru-X)Al alloys are due to electronic topological transitions.
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| 9. |
- 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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| 10. |
- Isaeva, Leyla, et al.
(författare)
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Ab initio Phonons in Magnetic Ni2MnAl
- 2011
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Ingår i: Japanese Journal of Applied Physics. - : Japan Society of Applied Physics / Japanese Journal of Applied Physics; 1999. - 0021-4922 .- 1347-4065. ; 50:5, s. 05FE07-
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we report the results of ab initio studies of electronic and dynamic properties of nickel based Heusler alloy Ni2MnAl. The total magnetic moment and elastic constants were also evaluated and compared to experimental results where possible. We found that the phonon dispersion relations calculated in this work within the linear response method did not reveal any softening of the transversal acoustic mode TA(2) along [xi, xi, 0] direction in accordance with the experiment and in controversy to previous theoretical studies.
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