Sp-d Hybridization Research Articles

Electronic structures and stability of Ag-In-Ca surfaces

Surface properties and stability of quasicrystal-related complex metallic compounds Ag-In-Ca has been studied theoretically. Optimal structures of surface is obtained by relaxing the atoms in a slab to their force-free positions by the first-principles method. It is found that, after relaxation, In is at topmost position near the vacuum, Ag intrudes into the bulk and Ca is located at intermediate layers between In and Ag. To simulate STM images for the slab model, we calculate the charge distribution constructed from the electronic states in an appropriate energy range. We find that bright contrast is observed on different subsets of the In sites on surface for the charge distributions calculated from occupied and unoccupied states. Roles of the low-lying unoccupied Ca-3d states and the sp-d hybridization on surface electronic structures are discussed.

Entropy of mixing for AgxIn1−x and AgxSn1−x liquid binary alloys

The entropy of mixing for Ag(x)In(1-x) and Ag(x)Sn(1-x) liquid binary alloys has been systematically investigated by using the perturbation theory. The interionic interactions as one of the basic ingredients are described by a local model pseudopotential. Since the metals forming the concerned alloys are less simple in nature the effect of the sp-d hybridization is appropriately taken into account through the interionic interactions. Results of our calculations across the full range of Ag concentrations are found to be good in agreement with the available experimental data.

Electron localization, the psudogap, and replica symmetry breaking in the quasicrystal-like system

We have discussed the origin of psudogap around the Fermi energy in the Al-based quasicrystal-like system by using the termal Green's function technique and the effective Lagrangian of diffusion modes, taking into account the sp-d hybridization.

Amorphous/crystalline transition of copper at room-temperature

When a glassy alloy Cu 60.6Zr 29.4Ti 10.0 ribbon was immersed in weak acid HF solution at room-temperature, selective complete leaching out of the Zr and Ti elements occurred, resulting in the formation of a self-organized crystalline copper ribbon with grain size of 32 nm, by accelerated self-diffusion of Cu. Since the glassy alloy is formed by spd hybridization bonding, based on a combination of valence electrons ( Eg) that exceeds the electrons ( Ec) predicted by crystalline metallic bond theory, disappearance of its extra valence electrons, i.e., Δ E ( Eg – Ec = 0.24 eV) for copper, due to leach-out of the Zr and Ti elements, facilitates on crystallization of the copper agglomerate.

Role of valence electrons for formation of glassy alloys

The role of valence electrons for formation of glassy alloys was investigated as a function of their valence electron concentration (VEC). The glass transition temperature T g of 121 kinds of glassy alloys can be expressed as a linear function of VEC: T g = 131VEC + 65 (2.3 < VEC < 5.2) for metal/metal bonding type and T g = −240VEC + 2408 (6.6 < VEC < 9.1) for metal/metalloid bonding one. The thermal stability of the glassy alloys increases by the unsynchronized resonance of electron-pair bonds, and decreases due to increase in covalency by metalloid elements, with an increasing number of valence electrons, respectively. Ab initio molecular orbital calculations of the optimized structures for the Mg monoanion clusters warranted application of the valence electron rule, which is based on a valence electron contribution associated with spd or spf hybridization for glass formation.

Electronic and Magnetic Properties of an Fe Monolayer Hosted between Graphene Sheets

We investigate the magnetic properties of an Fe monolayer residing between two graphene sheets with the use of the full-potential linearized augmented plane wave method within the generalized gradient approximation. We consider three Fe monolayers of di erent morphologies sat in the middle between two C(0001) layers. In the densest monolayer, Fe atoms occupy each hollow position available between C(0001) layers and in the least dense structure, the occupancy is 50 %. The equilibrium interlayer distance is determined through total energy calculations and the electronic and the magnetic properties of the equilibrium structures are discussed. The calculated magnetic moments on Fe atoms are 2.23 B for dense structures and 2.03 B for the structure with the largest interatomic distance. The least dense structure was found to be half-metallic with a total magnetic moment per unit cell of 2.0 B . For this structure, an energy gap is found for the majority spin channel. In the investigated systems, the sp-d hybridization between C and Fe atoms plays an important role and is noticeable in less dense structures. The magnetic properties of an Fe monolayer may be adjusted by controlling both the density of the monolayer and the interlayer distance in the system.

Entopy of formaton for AgxIn1-x liquid binary alloys

The entropy of formation for AgxIn1-x liquid alloys has been system systematically investigated by using the perturbation theory up to first order. The interionic interactions as one of the basic ingredients are described by a local model psudopotential. Since the metals forming the concerned alloys are less simple in nature the effect of the sp-d hybridization is appropriately taken into account through the interionic. Results of our calculations across the full range of Ag concentrations are found to be in good agreement with the available experiment data.

Electrophysical and structural-sensitive properties of liquid In2Te3 with 3d metal admixtures

Temperature dependencies of the electrical conductivity (up to 1700K), thermoelectric power (up to 1700K) and shear viscosity (up to 1150K) of the liquid semiconducting alloy In2Te3 with 3d metal admixtures were investigated. It was shown that small amounts (up to 3%) of Ti, V, Fe, Ni increase the electrical conductivity and slightly affect the thermoelectric power values. All the admixtures decrease the viscosity. The In2Te3 is regarded as a double-structured melt with a low-temperature loose-packing structure with crystalline features and a high-temperature dense-packing metallic structure. A melting process implies a structure rearrangement from the short-range structure with a spatial covalent bonds distribution to the more dense-packed structure of the linear chain type. The impurity d-states are manifested in the sp-d hybridization phenomenon.

Dual Relationship Between Large Gold Clusters (Antifullerenes) and Carbon Fullerenes: A New Lowest‐Energy Cage Structure for Au50.

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Electronic rule for formation of glassy alloys

The glass transition temperature Tg of 100 kinds of glassy alloys can be expressed as a function of their valence electron concentration (VEC): Tg=131VEC+57 for metal/metal bonding type and Tg=−236VEC+2375 for metal/metalloid bonding one. The electron valences of the constituent elements of the glassy alloys are somewhat larger than those predicted by crystalline metallic valence bond theory, suggesting a valence electron contribution associated with spd or spf hybridization for glass formation. Ab initio molecular orbital calculations of the optimized structures for Mg monoanion clusters warranted application of the valence electron rule.

Dual Relationship between Large Gold Clusters (Antifullerenes) and Carbon Fullerenes: A New Lowest-Energy Cage Structure for Au50

Recent theoretical prediction and experimental confirmation of cage configurations for Au clusters have stimulated considerable interest in finding novel gold clusters exhibiting high stability. We use a dual relationship between gold antifullerene cages with all triangular faces and carbon fullerenes with all degree 3 vertices to construct a large number of Au50 antifullerene cages by omnicapping and dualization procedures. Among these cages we find a new D6d cage as the lowest-energy configuration of Au50. The unusual stability of this new Au50 cage is associated with spherical aromaticity and sp-d hybridization.

The influence of nickel dopant on the microstructure and optical properties of SnO2nano-powders

The microstructure and optical properties of Ni-doped SnO2 nano-powders are studied in detail. By Ni-doping, not only the grain size reduces, but also the grain shape changes from nano-rods to spherical particles. The crystallization becomes better with annealing temperature increasing. The band gap energy decreases as nickel doping level increases. The sp-d hybridization and alloying effect due to amorphous SnO2-x phase should be responsible for the band gap narrowing effect. Nickel dopant does not change the photoluminescence (PL) peak positions.

Medium-ranged interactions of transition-metal (3d and 4d) impurity pairs in Al and atomic structures of Al-rich Al–transition-metal alloys

We give systematic ab initio calculations for the interaction energies (from first to eighth neighbors) of impurity pairs X–X (X = Sc–Zn, Y–Cd) in Al and discuss the micromechanism of the structural stability of Al-rich AlX alloys. The calculations are based on the generalized gradient approximation in the density-functional theory and employ the all-electron full-potential Korringa–Kohn–Rostoker Green's function method for point defects, which guarantees the correct embedding of the cluster of impurities and vacancies in an otherwise perfect crystal. We show: (1) the fundamental features of phase diagrams of these alloys, such as ordering and segregation, are understood by the sign of first-neighboring X–X interaction energies; (2) the structural stability of Al-rich AlX alloys such as L1 2 (Al 3Sc and Al 3Y), DO 22 (Al 3V and Al 3Nb), and Mackay icosahedron in AlMn quasicrystal, are understood qualitatively by using the medium-ranged and oscillating X–X interactions, due to the strong sp-d (Al–X) hybridization; (3) the strength and oscillating behavior of the medium-ranged X–X interaction energies are specified very well by the d-electron numbers of X impurities.

GROWTH BEHAVIORS AND ELECTRONIC STRUCTURES OF Na AND Cu NANOCLUSTERS: THE ROLE OF sp–d HYBRIDIZATION

Ab initio calculations of the atomic and electronic structures of Cu N and Na N (N = 2 - 22) clusters show similar growth behaviors. These can be characterized into 3 regimes: planar, layered and 3D structures. Atomic structures lead to anomalies in the even-odd alternation behavior of the second order energy difference for N = 16 and 17 in both Cu N and Na N. The effects of sp-d hybridization on the atomic and electronic structures of Cu N clusters are discussed.

Ellipsometric study of the electronic structure ofGa1−xMnxAsand low-temperatureGaAs

We have measured the optical constants of GaMnAs from 0.62 eV to 6 eV, using spectroscopic ellipsometry. The second derivatives of the dielectric function are examined through a critical point analysis. The E1 critical point shifts to higher energies with increased doping of Mn, while all other critical points appear unaffected. The evolution of the critical points results from the interplay between band gap renormalization from ionized impurities and sp-d hybridization of the Mn induced impurity band and GaAs valence and conductions bands.

Interpretation of the Hume-Rothery rule in quasicrystals and their approximants

We have performed the LMTO-ASA band calculations for the γ-phase Cu 5Zn 8 compound, the Frank–Kasper type Al 30Mg 40Zn 30 and Al 52.5Li 32.5Cu 15 1/1–1/1–1/1 approximants. In γ-brass, where d-states exist in the middle of the valence band and the sp-d hybridization effect is significant near the Fermi level E F, we show that it is critically important that the {3 3 0} and {4 1 1} zones satisfy the Hume-Rothery matching rule and that they are strongly coupled with the sp-d hybridization to produce a deep pseudogap across E F. In the nearly-free-electron-like Al–Mg–Zn approximant, it is shown that the {5 4 3}, {7 1 0} and {5 5 0} zone planes are essentially responsible for a pseudogap at E F. In the Al–Li–Cu approximant, the deep pseudogap at E F is proven to arise mainly from the Al-3p/Al-3p hybridization effect, but that the {6 3 1} zone effect is still significantly important.

Spin properties of quantum wells with magnetic barriers. I. Ak⋅panalysis for structures with normal band ordering

The electronic band-edge spectrum of magnetic semiconductor quantum wells containing a diluted magnetic semiconductor as one of the constituents is studied within the envelope-function formalism. The effects of Mn d electrons are explicitly included in a k p Hamiltonian which in the first approximation of perturbation theory is shown to be reduced to an effective Kane model. The sp-d hybridization leads to a spin-splitting effect. The results are applied to the system Cd 1 - x Mn x Te/CdTe. The spin-splitting effect is studied as a function of external magnetic field, well width, valence band offset and fraction of the magnetic atoms. The numerical results are in accord with experimental data.

Electronic properties of liquid Tl2Te, Tl2Se, Ag2Te, Cu2Te, and Cu2Se alloys

The dependences of the electrical conductivity σ(T) and thermoelectric power S(T) of Cu2Te, Cu2Se, Ag2Te, Tl2Te, and Tl2Se liquid semiconductors were experimentally studied at high temperatures and pressures (up to 25 MPa). The melts were shown to exhibit a minima in the dependences σ(T) and a maximum in S(T) at the stoichiometric composition M2X (where M=Tl, Ag, Cu; X=Te, Se). The results were interpreted on the basis of the Mott model with sp-d hybridization, taking into account the metal d state position with respect to the Fermi level.

Finite-size versus periodic effects in Ni/Co multilayers

The periodic effects on the electronic properties of Ni/Co magnetic multilayers grown in the (111) direction are investigated by studying superlattices and finite bilayers formed with the same unit block. Band structures and Fermi surfaces are calculated using a Green-function-matching method within a self-consistent empirical tight-binding model. Our results show strong sp-d hybridization of the electronic levels, the existence of nested multisheet Fermi surfaces, and the occurrence of d-derived spatially extended states in both superlattices and finite bilayers. Nevertheless, the superlattice periodicity increases the band degeneracy in the in-plane direction and changes the energy position of the superlattice electron levels with respect to those of the bilayer. The discrepancies result in different Fermi wave vectors for both systems, which may yield different transport and dynamical coupling characteristics for superlattices and bilayers.

Electronic structure of Al-Pd-Mn crystalline andquasicrystalline alloys

An experimental and theoretical analysis of the electronicstructure of Al-Pd alloys is presented. The experimental study,based on soft x-ray emission and absorption spectroscopies, isfurther extended to the case of quasicrystalline Al-Pd-Mn alloysand their approximants. The electronic structure is dominated bythe sp-d hybridization. The Al-sp band is strongly modified bythe interaction with the Pd-d states in the middle of thevalence band. Close to the Fermi level, hybridization with theMn-d states is found to enhance the structure induced pseudo-gapin the Al partial density of states, both in the icosahedral andthe decagonal quasicrystalline phases.