Surface properties of 3d transition metals

Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.     

Combined interpolation scheme for calculating the electron energy spectra of alloys of 3d transition metals

A model Hamiltonian is used as the basis of a combined interpolation scheme for calculating the spectra of ordered alloys of 3d transition elements with the CsCl and Cu₃Au structures. The parameters of the model Hamiltonian are found for the alloys FeCo and Co₃Ti and the histograms of the density of states are calculated at 165 points in 1/48-th part of the Brillouin zone. The results are evidence of the effectiveness of the use of such a combined interpolation scheme in calculating the integrated characteristics of the electron structure of alloys with large numbers of atoms in a unit cell.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 65–70, June, 1980.     

Catalytic effect of 3d transition metals on hydrogen storage properties in mechanically milled graphite

In this paper, we examined the catalytic effect of 3d transition metals on hydrogen storage properties in nanostructural graphite prepared by ball milling under hydrogen atmosphere. The Fe-doped nanostructured graphite shows the most marked hydrogen storage properties among the Fe-, Co-, Ni- and Cu-catalyzed graphite systems. The absorbed hydrogen concentration reaches up to ∼4 wt% by mechanically milling for 32 h (∼7 wt% for 80 h), and two peaks of hydrogen (mass number=2) around 730 and 1050 K were observed in the thermal desorption mass spectra (TDS). The starting temperature for hydrogen desorption was ∼600 K. On the other hand, the Co-doped graphite indicates that absorbed hydrogen concentrations reaches up to ∼2 wt% by mechanically milling for 32 h. The TDS spectrum showed only a broad peak around 1100 K, but the starting point for hydrogen desorption lowered down to ∼500 K. The Ni- and Cu-doped graphites did not show any significant improvement for hydrogen storage. These results suggest that the catalytic effect on hydrogen storage properties strongly depends on the affinity of graphite and doped metals.     

Theory of chemisorption of hydrogen on transition metals and their alloys

A theoretical discussion is given of the changes in the heat of chemisorption of a hydrogen atom upon alloying a group-VIII metal with a group-IB metal. The emphasis is on two concepts: the ensemble effect and the ligand effect. The ensemble effect ascribes the changes in the heat of chemisorption primarily to changes in the geometry of the adsorption complex, whereas the ligand effect also takes into account changes in bond strength due to a different intrinsic activity of the bonding metal atoms.     

Invar properties in the rare earth-3d transition metal alloys

The RCo₂ and R₂Fe₁₇ compounds (R = rare earth) exhibit Invar-like thermal expansion anomalies below their ordering temperatures. These spontaneous volume magnetostrictions are discussed by considering their magnetic properties. In RCo₂ compounds there is no intrisinc Co-moment is induced by the exchange and applied fields. The volume expansion anomaly is associated with the onset of the 3d magnetic moment. IN R₂Fe₁₇ compounds there is an intrisinc Fe- moment. Magnetic structures give evidence for positive and negative exchange interactions between Fe atoms which are strongly distance dependent. The thermal expansion anomaly is a result of this distance of the magnetic interactions.     

Energy of intermetallide formation for 3d transition metals

By the method of a model electron-density functional, the energy of alloy formation in the systems Fe-Ti, Co-Ti, Ni-Ti is calculated as a function of the volume, concentration, and degree of long-range order. The energy benefit of the appearance of compounds FeTi, CoTi, NiTi in the CsCl structure is established. For the given compounds, the equilibrium volumes and the magnitude of charge transfer are calculated. An analysis of the ordering energy as a function of the concentration and degree of long-range order is performed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 47–51, May, 1982.     

Trends in hydrogen chemisorption on transition metals

A systematic study of H adsorption on the close-packed surfaces of the transition metals in the 3d and 4d series is presented. The effect of the TM d band on the chemisorption bond is investigated, by embedding a cluster of TM muffin tins at the surface of an effective jellium-like medium. It is found that the broad and incomplete H/jellium resonance is narrowed, shifted down and made to contain more electrons as a result of hybridization with the TM d states. These effects are larger in the case of the 4d metals, thus indicating a greater participation in the chemisorption bond of the d electrons for these metals than for the 3d metals. Calculation of one-electron energy differences on going from the H on jellium system to that of H on the TM cluster are presented. Trends for the one-electron energy differences are compared to trends in experimental chemisorption energy. H adsorption in the three-fold hollow site with no secondlayer TM atom below the H site is favoured for the hcp metals, while no discernible preference between the two hollow sites is recorded for the fcc metals, with the exception of Rh where the site with no second-layer TM atom below is preferred.     

X-ray absorption spectra: K-edges of 3d transition metals,L-edges of 3d and 4d metals,and M-edges of palladium

The X-ray absorption spectra of the 3d and 4d transition metals have been calculated within the single-particle approximation by a new linearized augmented plane wave method. The spectra, calculated with sharp atomic and band-structure single-particle levels, have been convoluted with a Lorentzian broadening function whose width is the sum of that of the core hole and the excited electrons. Plots are shown for (i) the K-edge fine structures up to at least 100 eV above the edge for Ca, Ti, Cr, Co, Cu, and Zn, (ii) the L_{2, 3} white lines for Ca, Ti, Cr, Co, and Cu, (iii) the L₃ white lines for Sr, Zr, Nb, Ru, Rh, and Pd, and (iv) the M_{2, 3} and M_4,5 spectrum of Pd. Systematic features which depend on the crystal structure and the placement of the Fermi level with conduction band are briefly discussed.     

Electron correlations in alloys of simple and transition metals

The effect of dynamical electron-electron correlations on the electronic structure of the paramagnetic disordered binary alloy of the transition and simple metals is studied for the Anderson model extended to arbitrary concentration of the transition metal impurities. We use the terminal-point approximation for the many-body quantities, which allows us to solve the random part of the problem within the single-site approximation. The many-body part of the problem is treated within the selfconsistent T-matrix approximation, valid for low, but finite concentration of particles ( ? 0.3/atom/spin). For low concentration of the transition metal impurities we obtain results identical with those for the Anderson model. The theory is illustrated numerically for a simple bandstructure model.     

Analysis of the liquid structure of 3d transition metals from the Wills-Harrison model

Calculations of the liquid structure of 3d transition metals from the effective pair interactions of Wills and Harrison are performed by using the optimized random phase approximation in order to point out the influence of thes-electron pseudopotential on the repulsive and attractive forces governing the liquid structure. Our results are compared to those obtained in the Weeks, Chandler Andersen approximation and in the thermodynamic variational method.     

Features of laser radiation interaction with metals having cryogenic temperature

In this paper we determine the features of the thermophysical processes involved in the interaction of laser radiation with metals that have cryogenic temperature. To do so, we use a one-dimensional model that involves heating a semi-infinite solid by a point thermal source with a constant flux density. Temperature fields, heating and cooling rates in the laser-irradiated zone for iron and titanium at the ambient temperatures of 77 (liquid nitrogen), 293 and 573 K were calculated. The intensity of the laser irradiation enabled the melting temperatures of 1933 K and 1812 K on the Ti and Fe surface, respectively, to be reached. The duration of the laser pulse was 4.5 ms. We show that a drop in ambient temperature from 573 to 77 K leads to a rise in cooling rate from 3.25 × 10³ and 6.4 × 10⁶ K/s to 4.25 × 10³ and 1.3 × 10⁷ K/s in the Ti and Fe targets, respectively. Agreement was good between the calculated depths of melting and phase transformation isotherms and the experimental depths of the interfaces of melting and heat-affected zones.