Contribution Of D-electrons Research Articles

Structural, vibrational and electronic properties of D03 FeNi3

The Fe-Ni invar alloys attract the great interest of researchers due to their anomalously low coefficient of thermal expansion for Fe-rich compositions and numerous technological and practical applications. The structural, vibrational and electronic properties of D03 FeNi3 studied using the first-principles plane wave self-consistent method with the Ultrasoft pseudopotential scheme under the framework of DFT. Calculated equilibrium lattice constant and isothermal bulk modulus for D03 FeNi3 presented with the other available results. Existence of imaginary phonon frequencies in the phonon dispersion curves of D03 FeNi3 suggest the dynamical instability of it. Significant contribution of d-electrons to the total electronic density of states is in agreement with the previously reported work. Electronic charge density plots for D03 FeNi3 predict weak metallic bonding between Fe and Ni compared to between Fe-Fe metal atoms. Fermi surface topology exhibit electron and/or hole character at different high symmetrical points of the Brillouin zone based on the crossing of bands at EF in the electronic band structure. Conclusions based on the phonon dispersion curves, phonon density of states, electronic band structure along with the total and projected density of states, electronic charge density and Fermi surface are summarized.

Beyond the Drude model in transport and optical properties of dense plasma of silver

We calculate optical and transport properties of dense silver plasma via quantum molecular dynamics together with the Kubo-Greenwood formalism and compare the results with ones obtained using a semi-analytical Drude-like model. The quantum molecular dynamics highlights an important contribution of d-electrons to the properties of silver, and thus the thermal conductivity is not described by the Drude model. At the same time, the imaginary part of dielectric function can be fitted by the Drude-like model with reasonable accuracy in the optical range of frequencies.

Magnetic Phase Transition in Antiferromagnetic SrMnO3 Perovskites

We study thermal properties of SrMnO3 starting from analysis of the low-energy electronic structure of the Mn4+ ion in oxygen surroundings. As a start point of the studies, simulations of a SrMnO3 unit cell were performed with using the density functional theory (DFT). The DFT calculations have revealed ionic character of the compound. In the next stage of calculations the Mn4+ ion was treated as an atomic-like strongly-correlated 3d3 system with the 28-fold degenerated ground term 4F. This degeneracy is lifted under the combined action of the dominant octahedral crystal field and the on-site spin-orbit coupling. This study was concentrated on the explanation of the temperature dependence of the specific heat showing a pronounced λ-type peak at TN. We have calculated the d-electron contribution to the specific heat both in the antiferromagnetic and paramagnetic states. We have found that the entropy of the magnetic contribution is close Rln4 - a value expected from the 4A2g ground subterm of the Mn4+ ions. e.g. 11.5 J/Kmol.

Nonlinear Optical Constants of Superionic Conductors: A Study from the Bond Orbital Theory

According to the bond fluctuation model of superionic conductors, the polarizability of a material that exhibit high ionic conductivity must be large. That is, the model predicts that ion conducting materials must have large values of optical constants. This prediction has been confirmed recently, through a comparative study of the nonlinear optical constants of ion conducting and non-conducting glasses. In the present report, the values of the nonlinear optical constants χ (3) of R 2 O–B 2 O 3 (R = Rb, Cs, Ag) glasses have been estimated by using the bond orbital theory. For the Rb 2 O–B 2 O 3 and Cs 2 O–B 2 O 3 glasses, a good agreement between the calculated and the measured values has been found. On the other hand, for the Ag 2 O–B 2 O 3 system, a deviation was observed. Such a disagreement has been explained by taking into account the contribution of d-electrons of the Ag ions, which plays also a fundamental role in the ion transport mechanism.

Calculation of longitudinal surface plasmon frequencies in noble metal nanorods

The longitudinal surface plasmon oscillation frequencies of long enough noble metal nanorods are analyzed theoretically. An expression for frequency dependence on aspect ratio accounting for the contribution of d-electrons into the dielectric function of metal is obtained. The results of calculations for gold nanorods in aqueous solution are compared with various experiments and good agreement is demonstrated. An analytical expression for the surface plasmon resonance sensitivity with respect to changes in the refractive index of surrounding media is obtained.

Facing target sputtered iron-silicide thin film

The FeSi x thin films with the flatness to an atomic scale for mechanical and optical applications can be grown by a facing target sputtering method. Optical properties indicate the films contain nano-crystalline FeSi 2. The nano-indentation hardness of 10 GPa was obtained. An interesting point is that Young's modulus is larger than that of the carbon-based materials with the same hardness. This means that the FeSi x is more elastic, which could be characteristic of the chemical bonding of the FeSi 2 with the large contribution of d-electrons. Furthermore, results of the Hall measurement at room temperature shows that the films have p-type conductivity, a carrier concentration of p = 2.49 × 10 20 cm − 3 and a Hall mobility of μ = 6.42 cm 2 V − 1 s − 1 .

Synthesis and Magnetic Studies of Nanocrystalline Nickel Nitride Material

Single domain Ni 3 N nitride particles are synthesized by simultaneous decomposition and nitridation in ammonia atmosphere of [Ni(NH 3 ) 6 ](NO 3 ) 2 complex crystals at 650 K. The Ni 3 N phase crystallizes in the hexagonal structure with unit cell parameters a = 4.624(4) A and c = 4.316(4) A, and has a crystallite size of 16 nm. In TEM study, these nanosize particles show spherical shape, and form particle aggregates of 18 nm size. Ni 3 N particles exhibit a Curie temperature of T C = 634 K. In the field dependence magnetic measurements, the presence of hysteresis loop indicates ferromagnetic behavior with σ s = 1.678 emu/g, σ R = 0.50 emu/g and μ 0 H c = 0.022 T. In this phase, the density of states (DOS) of Ni is dominated by 3d states and is mixed with 2p DOS of N. The contribution of d-electrons in the intra-band polarization affects the magnetic moment of Ni and thus the magnetic moment of Ni 3 N.

Atomistic simulation of titanium. I. A bond-order potential

Abstract The bond-order potential for hcp Ti has been constructed in the framework of a tight-binding description of the binding energy. In this scheme the energy consists of two parts: the bond part that comprises the d-electron contribution to bonding, and a pairwise part. Both parts contain fitting parameters but are treated independently. The bond part reproduces the most important characteristics of the d-band and Cauchy pressures, and the pairwise part complements the bond part so as to reproduce exactly the equilibrium lattice parameters and to a good approximation the elastic moduli. The potential is tested by examining the mechanical stability of the hcp lattice with respect to a variety of large deformations. It is applied to a study of dislocation behaviour in Ti in the accompanying paper, part II.

From the transition metals to the rare earths — via the actinides

The calculated equations of state of the transition metals are dominated by the d-electron contribution to bonding and at the end of the 3d series the metals become magnetic. In contrast, the calculated equations of state of the rare earths are characterized by the lack of any f-electron contribution to bonding at ambient pressure and the metals are normally magnetic. Electronic structure calculations for the light actinides show that they fall naturally between the transition metals and rare earths. There is a large f-electron contribution to bonding, analogous to the d-electron contribution in the transition metals, and the light actinide metals are not magnetic. Relativistic effects upon the valence electrons are also much larger than in the transition metals and in actinide compounds, which frequently are magnetic, the composition of the magnetic moments contains features of both rare earth and transition metal magnetism.

Hybridized nearly-free-electron tight-binding-bond approach to interatomic forces in disordered transition-metal alloys. I. Theory.

A hybridized nearly-free-electron tight-binding-approach to interatomic forces in disordered transition-metal alloys is presented. The s-electron contribution to the pair and volume forces is calculated in a pseudopotential perturbation expansion; the d-electron contribution, within a tight-binding-bond approach. The bond order is calculated analytically on a Bethe-lattice reference system. It is shown that the bond order depends strongly on the form of the d band in the alloy. As the electronic density of states changes from a common band to a split-band form, the pair forces in the alloy change from a set of additive pair potentials to nonadditive potentials with a strong preference for the formation of pairs of unlike atoms and short bond distances in the AB pairs. This is illustrated for a series of Ni-M alloys (with transition metal : M=Y, Zr,. . ., or Pd) as a function of alloy composition.

Surface core-level spectroscopy of Cu(100) and Al(100).

We present experimental and theoretical results for the surface core-level binding-energy shifts of Al(100), representative of an sp metal, and Cu(100), representative of a transition metal. Our analysis of these results leads to a unified interpretation for the different behavior of sp and transition metals. The d-electron contribution to smaller surface core-level binding energies is elucidated.

Resistivity and superconductivity of uranium based metallic glasses

Amorphous U-Fe, U-Co and U-Ni alloys were prepared by splat quenching over the uranium concentration range of 50 – 83 at%. The temperature dependence of the electrical resistivity, ρ (T), was investigated in the range of 4.2 – 300 K. The results below the Debye temperature ( θ ≃ 165 K) may be explained within the frame of the extended Ziman theory and the paramagnon model. The concentration dependence of ρ and of the superconducting transition temperature T c might be explained by the variation of the d-electron contribution.

Induced anisotropy of conductivity and electronic structure of glassy ZrNi alloys

A change in resistivity, due to uniaxial stress in the elastic region has been measured for several amorphous Zr 1− x Ni x alloys. The strain gauge factor ( K) decreases linearly with x and is independent of temperature (80 K < T < 300 K) which makes these alloys useful for strain gauges. The induced anisotropy of conductivity (γ) at room temperature was measured and the change in resistivity with volume (−δ) evaluated. The values of δ are in good agreement with those obtained from the measurements under hydrostatic pressure. In Zr 1− x Ni x alloys γ decreases faster with x than in Zr 1− x Cu x , and reaches zero for x = 0.65. This variation of γ with x compares well with the observed decrease in the electronic density of states at the Fermi level with x and lends further support to the relation between γ and the d-electron contribution to conductivity.

Physisorption interaction of H 2 with simple metals

Calculations of the physisorption interaction between a H 2-molecule and simple metal surfaces are reported. The physisorption wells of simple and noble metals having the same s-electron densities are markedly different. The former are shallower because there is no contribution of d-electrons to the Van der Waals force. The physisorption energies are found to depend strongly on the bulk density, varying from 25 meV (Al) to 2.7 meV (K). Results for three Al surfaces show a face dependence due to the different work functions that may be measurable.

Physisorption interaction of H 2 with simple metals

Calculations of the physisorption interaction between a H 2-molecule and simple metal surfaces are reported. The physisorption wells of simple and noble metals having the same s-electron densities are markedly different. The former are shallower because there is no contribution of d-electrons to the Van der Waals force. The physisorption energies are found to depend strongly on the bulk density, varying from 25 meV (Al) to 2.7 meV (K). Results for three Al surfaces show a face dependence due to the different work functions that may be measurable.

Improved description of the Van der Waals interaction in physisorption

The attractive interaction between an atom and a metal surface is calculated, taking into account the d-electron contribution to the metal response, together with an atomic polarizability going beyond the dipole approximation. A numerical calculation is presented for helium on noble metals, giving a slightly deeper physiosorption well compared to the “standard” treatment.

On the magnitude of the electrical resistivity of liquid and glassy transition metal alloys

We discuss the magnitude and the concentration dependence of the electrical resistivity of liquid and glassy transition metal alloys. We present the measured resistivities of Cu-Zr glasses (25–75 at % Zr) and analyze the results in terms of a simple two-band model. On the basis of a semi-empirical fit of the experimental data, we conclude that at the Zr rich end, the contribution of d-electrons to the total conductivity should not be neglected.

Superconductivity in tight-binding approximation

An interpretation of Barišić's relation for transition elements between the d-electron contribution to the cohesive energy and the local atomic parameter η is presented. We extend this relation to a lattice with more than one atom per unit cell in the tight-binding approximation of rigid ions. It is conjectured that Barišić's relation is correct to first order approximation for transition metal alloys, provided the phonon induced d- d coupling is the dominant mechanism for superconductivity.

On the nature of cohesion in copper

The origin of cohesion in copper is discussed on the basis of calculations performed in a simplified nearly-free ( s) electron-tight binding ( d) electron model. While the atomic radius dependence of the s-electron energy is obtained similar to earlier ab initio results, the d-electron contribution to the total energy is found not to be the traditional monotonic repulsion, but slightly attractive in the neighbourhood of the observed lattice spacing.

Electronegativity and crystal field splittings in rare earth compounds

Crystal field studies in a variety of 4 f-and some 5 f electron-systems reveal a correlation between crystal field splittings, i.e. sign and charge strength of simple ligands and their electronegativities. Deviations occur in several very dilute f.c.c. noble metals, as well as noble metal compounds presumably due to the d-electron contribution and perhaps ill-defined valence states, in particular in transition metal compounds.