S. E. Kulkova

Hydrogen adsorption on Pd/TiFe (110) surface

Adsorption of hydrogen on the TiFe (110) surface covered by palladium monolayer was investigated using the full potential linearized augmented plane wave method within the local density approximation. Influence of palladium coating to adsorption properties of the TiFe (110) surface as well as difference it from Pd/TiFe (100) are discussed.

Hydrogen adsorption on low-index surfaces of B2 titanium alloys

Systematic first-principles calculations of hydrogen adsorption on two surfaces (001) and (110) of B2 titanium alloys with inclusion of complete relaxation of the system are performed for the first time within the electron-density functional theory. The equilibrium sites of hydrogen on metal surfaces are determined with respect to the surface termination and its orientation. It is shown that the hydrogen adsorption on the (001) surface in the series of titanium alloys under investigation is more preferred on the titanium-terminated surface. The relaxation effects change the adsorption energy by ∼0.10–0.25 eV, although, in general, tendencies revealed for ideal films remain unchanged. Among the hydrogen sites studied on the TiMe(110) surface, the pseudo-threefold-centered F1 site with predominance of titanium atoms is most preferred for the alloys of the beginning of the series (TiFe, TiCo). For the TiNi, TiPd, and TiPt alloys, the adsorption energies in the F1 site and the titanium bridge site are nearly equal. The calculated curves of local and partial densities of states are used to explain the mechanisms of interaction between hydrogen and the surface.

Theoretical study of the electronic structure and hydrogen adsorption properties in B2-TiFe thin films with Pd coating

Abstract The electronic structure of Pd-covered TiFe (0 0 1) surface was studied using the full-potential linearized augmented plane wave method with local density approximation for the exchange-correlation potential. The electronic structure changes introduced by Pd in the surface layers of B 2 -TiFe (0 0 1) are analyzed. The influence of hydrogen and oxygen on the electronic properties and surface electronic structure of clean B 2 -TiFe (0 0 1) and with monolayer of Pd is discussed.

Electronic structure and adhesion on metal-aluminum-oxide interfaces

This paper reports on the results of the systematic analysis of the atomic and electronic structure of the Me/α-Al2O3(0001) interfaces for two series of isoelectronic metals (Me = Cu, Ag, Au and Ni, Pd, Pt), depending on the termination of the oxide substrate and the configuration of oxide films. The calculations have been performed by the pseudopotential method in the plane-wave basis set. The adhesion energy of metal films has been calculated depending on the cleavage plane. It has been shown that the adhesion energy is maximum at the oxygen interface, which is caused by the ion component in chemical bonding at this interface. The aluminum and aluminum-enriched interfaces are characterized by the metallic type of bonding. The local densities of states and the charge distribution near the interface have been analyzed. It has been demonstrated that oxygen vacancies at the interface substantially weaken the adhesion due to the partial breaking of Me-O bonds.

Changes in the electronic structure upon the B2–B19′ martensitic transformation in titanium-nickel

The self-consistent band structure of a TiNi intermetallic compound in two phases is calculated by the full-potential linearized augmented-plane-wave (FLAPW) method. The features of changes in the density of states upon B2–B19′ martensitic transformation are discussed. The influence of atomic positions on the electronic structure of the martensitic monoclinic phase is examined. The frequency dependence of the optical conductivity and the emission, absorption, and the characteristic electron-energy-loss spectra are calculated with due regard for the transition probability matrix element. The results of calculations are in reasonable agreement with the available experimental data.

Theoretical study of oxygen sorption and diffusion in the volume and on the surface of a γ-TiAl alloy

The oxygen sorption on the low-index (001), (100), and (110) surfaces of a γ-TiAl alloy is studied by the pseudopotential method with the generalized gradient approximation for the exchange-correlation functional. The most preferred sites for oxygen sorption in the bulk and on the surface of the alloy are determined. The titanium-rich octahedral site is shown to be preferred for oxygen sorption in the bulk material. The effect of the oxygen concentration on the atomic and electronic structures of the stoichiometric TiAl(100) surface is studied. It is shown that, at the first stage of oxidation, oxygen prefers to form bonds with titanium. The energy barriers for oxygen diffusion on the stoichiometric (100) surface and in the bulk of the material are calculated. The energy barriers are shown to depend substantially on the local environments of oxygen and to increase during diffusion from titanium-rich sites. The most possible mechanism of oxygen diffusion from the (100) surface to the bulk of the material is oxygen migration through tetrahedral sites.

Chlorine adsorption on the InAs (001) surface

Chlorine adsorption on the In-stabilized InAs(001) surface with ζ-(4 × 2) and β3′-(4 × 2) reconstructions and on the Ga-stabilized GaAs (001)-ζ-(4 × 2) surface has been studied within the electron density functional theory. The equilibrium structural parameters of these reconstructions, surface atom positions, bond lengths in dimers, and their changes upon chlorine adsorption are determined. The electronic characteristics of the clean surface and the surface with adsorbed chlorine are calculated. It is shown that the most energetically favorable positions for chlorine adsorption are top positions over dimerized indium or gallium atoms. The mechanism of chlorine binding with In(Ga)-stabilized surface is explained. The interaction of chlorine atoms with dimerized surface atoms weakens surface atom bonds and controls the initial stage of surface etching.

Point defects and mechanical behavior of titanium alloys and intermetallic compounds

First principles calculations were carried out to investigate the energetics of point defects, including solute atoms, vacancies, and antisite defects, in titanium solid solution and intermetallics. Their influence on the mechanical behavior of titanium alloys and intermetallic compounds were discussed. The self consistent procedure proposed by the authors was applied to TiAl intermetallic compounds. The ordering parameter was redefined to include the contribution of vacancies to the disordering of intermetallic compounds, so that the new approach can be applied to both strongly and weakly ordered compounds. Concentrations of point defects of various kinds can be estimated for intermetallics of different composition at different temperature. The solid solution strengthening of alloying elements through short range ordering was studied for titanium alloys and the solid solution hardening rate was estimated for various alloying elements. The solute-vacancy interaction in titanium alloys was calculated and its influence on the diffusion and creep behavior was discussed. These calculations provided some useful information for the selection of alloying elements in designing new titanium alloys.

Interaction of hydrogen with impurities in group IVB metals

The energetics of hydrogen bonding with Group IVB metals and the interaction of hydrogen with impurities of 3d-transition and simple metals (Al, Ga, Si, Ge) have been investigated using the projector-augmented-wave (PAW) method within the framework of the density functional theory (DFT). It has been found that the solubility of hydrogen in Ti, Zr, and Hf increases upon their alloying with metals located in the middle of the 3d period. The relationship between the interaction energy of hydrogen with impurities, the lattice distortions, and the electronic structure of the studied systems has been analyzed. It has been shown that impurities do not affect the preferred hydrogen sorption positions in titanium but can change these positions in zirconium and hafnium. The influence of impurities and hydrogen on the electronic structure of metals has been examined. The obtained results have demonstrated that, in the studied metals, the interactions of hydrogen with impurities of 3d-transition and simple metals are determined by different mechanisms: the attraction of hydrogen by transition metal impurities is caused by the size effect, whereas the repulsion of hydrogen by simple metals can be associated with the electronic factors.

Change in the electronic properties of an InAs (111)A surface at oxygen and fluorine adsorption

Based on ab initio calculations, the adsorption of oxygen and fluorine on reconstructed (2 × 2) and unreconstructed (1 × 1) InAs (111)A surfaces is studied. The most stable adsorption positions are determined. It is shown that adsorption of oxygen on both surfaces gives rise to electronic states in the band gap. The preferential positions for oxygen adsorption on an InAs (111)A (2 × 2) surface are those where oxygen is bonded both to indium atoms and to arsenic atoms in the surface layer and also the vacant site between three indium atoms (the “In-hollow position). Adsorption of fluorine brings about a pushing of the surface states out of the band gap; the position above indium atoms (the “In-top position) is preferential for adsorbed fluorine. Adsorption of fluorine on an InAs (111)A (1 × 1) surface leads to the elimination of the surface state formed by indium p orbitals and to an unpinning of the Fermi level.