Alloys Of Simple Metals Research Articles

Electrical Transport and Electronic Structure Calculation of Al-Ga Binary Alloys

The Harrison first principle pseudopotential technique based on the concept of orthogonalized plane waves has been used to study the liquid electrical resistivity and other physical properties viz., Knight shift, Fermi energy and electronic density of states of liquid binary alloys of simple metals. We have also performed a first-principles calculation of the electronic band structure of Al–Ga binary alloy at equiatomic composition employing the full-potential linearized augmented plane wave method. Total energy minimization enables us to estimate the equilibrium volume, bulk modulus and its pressure derivative. We have also described the total density of states and the partial density of states around the Fermi energy.

On Superconducting Transition Temperature in Amorphous Alloys of Simple Metals

On Superconducting Transition Temperature in Amorphous Alloys of Simple Metals

Atomic structures and electrical resistivities of ternary liquid alloys

A self-consistent energy-independent non-local model pseudopotential theory has been developed for ternary alloys of simple metals for the first time. For K - Rb - Cs alloys, the partial structure factors are obtained by a solution of the standard Percus - Yevick equations for a ternary mixture of hard spheres. These partial structure factors are applied to calculate the electrical resistivities in the full concentration range of the alloy using the Ziman theory. Both the structure factors and the pseudopotential calculated form factors have been shown to be concentration sensitive. It has been shown that the electrical resistivities of the binary liquid alloys, such as K - Rb or K - Cs which exhibit nearly ideal structural behaviour, can be predicted to be in reasonable agreement with the experimental data. For ternary alloys, the calculated electrical resistivities vary smoothly with the concentration of each constituent, follow a well defined pattern in continuity and form a so-called `electrical resistivity surface'. The results suggest that both the second-order non-local pseudopotential perturbation theory and the Ziman formalism are quite applicable in the prediction of the electrical resistivities of the multi-component alloys.

Electronic properties of the liquid alloys AlCa and AlBa

The electrical resistivity, ϱ, its temperature dependence, α (≠ (1/ϱ)/(dϱ/dT)), and thethermopower, S, of the liquid alloys AlCa and AlBa were measured over the full composition range. Large values of ϱ and negative α over rather wide ranges of composition are found, implying that these unusual alloys of simple metals are non-free-electron in character. Comparisons between ϱ( c) and α( c), where c is the atomic fraction of either Ca or Ba, make it unlikely that the Mooij rule is affective here. Rather sharp minima in α( c) and S( c) at the approximate compositions Al 2Ca and Al 2Ba, coupled with simple calculations, imply that some chemical short-range ordering at these stoichiometries occurs in the liquids. This conclusion is consistent with more complete calculations as well.

Electronic structure and hybridization effects in Hume-Rothery alloys containing transition elements

We present a systematic study of the electronic structure of Al-based Hume-Rothery alloys containing transition elements performed with the use of the linear muffin-tin orbital in atomic-sphere approximation method. Our analysis focuses on the formation of the pseudogap at the Fermi level leading to the stability of materials containing transition-metal elements in small concentration. From the self-consistent calculated density of states, we observe a strong deviation from the two classical limits: (a) the Friedel-Anderson virtual bond state's model and (b) the nearly-free-electron diffraction by some Bragg planes in the usual Hume-Rothery picture of simple metal alloys. Transition-metal atoms have a crucial role on electronic structure via the combined effect of the sp-d hybridization and of a strong interaction between the Fermi surface and a predominant Brillouin zone.

On the formation of the d bands in alloys of simple metals with d metals

The problem of the formation of the d resonances in alloys of Mg and Al with a number of d metals (Ni, Cu and Zn) has been investigated both experimentally and theoretically. High-resolution ultraviolet photoelectron spectroscopy (UPS) spectra have been taken for these alloys and the electronic structure has been calculated by the linear muffin-tin orbital (LMTO) method, within the atomic sphere approximation. The theoretical results allow for the interpretation of the shapes of experimental spectra, while it turns out that the widths of the d bands can be described by the Friedel-Anderson model only qualitatively.

Change of elastic constants on Al-Ti alloy by solid solutioning under high pressure.

Supersaturated solid-solution alloys of the Al-Ti system were prepared at a pressure of 5.4 GPa and a temperature of 800°C for 10 hours. The solid solubility was determined to be about 1.5 at%Ti by the X-ray diffraction technique. Changes of material properties (lattice parameter, elastic constants, density) for obtained solid solutions as a function of Ti concentration were estimated. The solid solubility of Ti in Al was increased to 1.5 at%Ti by the effect of the high pressure of 5.4 GPa. The lattice strain e0 was measured to be -0.088. The shear modulus of the solid solutions was increased with increasing Ti concentration. The rate of 125 GPa/(e/a) was obtained. This feature was different from those of solid solutions consisting of simple metal alloys.

Effect of pressure on electrical resistivity of Mg70Zn30metallic glass

AbstractThe variation of the electrical resistivity of amorphous simple metal alloy Mg70Zn30 as a function of non-hydrostatic pressure has been studied. Measurements have been made in the range 0–10 kbar. The resistivity is found to increase with increasing pressure.MST/982

The Electronic Density of States in Amorphous Binary Simple-Metal Alloys*

The Electronic Density of States in Amorphous Binary Simple-Metal Alloys*

Melting point trends in intermetallic alloys

We have examined the melting points of approximately 500 intermetallic binary alloys. We attempted to correlate the melting point behavior of the binary (1:1) alloys with a number of elemental variables including electron number, atomic size, orbital radii, electronegativity, etc. We find that a “Vegards's Law” of melting points works very well for predicting the melting points of binary transition metal alloys, i.e. the melting point of the alloy correlates with the linear average of the elementary melting points. However, this “law” works only moderately well for alloys involving simple metals. In addition, we find that transition metal alloys tend to have melting points below the averaged elemental melting points. This finding is in sharp contrast to simple metal alloys where the opposite trend is observed and it is indicative of fundamental differences between transition metal and simple metal binding. Finally, we have attempted to correlate deviations from a Vegard's law of melting with elemental variables. We found no strong correlation with elemental variables (or the heats of formation of the alloy in question) with the possible exception being a correlation with elemental volume changes upon alloying. The consequences of this correlation upon alloy design and metallic alloy formation are briefly discussed.

Surface segregation in simple metal alloys: An electronic theory

Surface segregation in simple-metal random binary alloys is studied via an electronic theory based on local ionic pseudopotentials and a linear-electron-response model appropriate for semi-infinite systems. Segregation of the larger species ions to the surface layer and (in most cases) a nonmonotonic layer concentration profile are predicted. The segregation of the larger species ions to the surface layer is driven by single-particle terms (Hartree-energy terms) in the total-energy expansion. These single-particle energy terms are independent of coordination number and relative positions of the ions but depend on the position of the surface layer relative to the inhomogeneous zeroth-order electron density at the metal surface, thus giving rise to crystal-face specificity. The concentration in deeper layers is determined primarily by effective interionic interactions. The electronic theory is compared with a nearest-neighbor pair-bond model, and it is concluded that the pair-bond model is not applicable to surface segregation in simple-metal alloys. The alloys considered in this paper are composed of the alkali metals K, Rb, and Cs. Concentration profiles as functions of temperature are presented for the (100) and (110) surfaces.

Magnetic susceptibilities of liquid binary alloys

A description of the concentration dependence of the magnetic susceptibilities of a number of liquid binary alloys of simple metals is effected in three stages. First, a previous pseudopotential formalism is extended to enable the calculation of the conduction electron diamagnetic susceptibilities in the pure liquid metals, Li, Na, K, Rb, Cs, In and Pb. These results are then combined with much earlier calculated values of the diamagnetic susceptibilities of the core electrons and with observed values, existing in the literature, of the total magnetic susceptibilities to infer the conduction electron paramagnetic susceptibilities of the above pure liquid metals. Second, the expressions for the two diamagnetic contributions are modified permitting the determination of their concentration dependence in a number of nearly-free-electron (NFE) like liquid binary alloys. The Landau theory of a Fermi liquid is used to infer the concentration dependence of the paramagnetic contribution. Third, Li-Pb, which is not NFE like over the entire concentration range is treated separately as a special but closely related case. The observed results for the concentration dependence of the total magnetic susceptibility are favourably reproduced, both for those alloy systems exhibiting smooth variations and for those with large variations.

Calculation of Knight shifts for liquid binary alloys of simple metals: charge-transfer effects

The authors examine the calculation of the direct contribution to the electron spin density at a nucleus in liquid binary alloys of simple metals by low-order pseudopotential perturbative methods. It is concluded that self-consistency requirements are sufficiently stringent so that it is simply impractical to use this approach and expect reasonable accuracy. Hence, in order to gain some physical insight into the problem, a simple model, using the concept of a charge transfer between ions, is proposed for the estimation of the total electron contact densities at a nucleus in the alloy. The results are applied to determine the concentration dependence of the corresponding Knight shifts and good agreement is found with observation.

Magnetic interference effect in the electrical resistivity of amorphous simple metal alloys: Mg-Zn(Gd)

Electrical resistivity in an amorphous simple metal alloy host Mg70Zn30 containing up to 4 at.%Gd has been studied. the 'non Kondo' upturn in resistivity at low temperature is interpreted in terms of conduction electrons scattering from correlated pairs of spins. A universal behaviour of excess resistivity per at.%Gd versus reduced temperature T/ theta s (where theta s marks the onset of excess resistivity) is observed. Comparison is made with theoretical predictions. Magnetic susceptibility data are found to correlate well with resistivity measurements. No significant attenuation of magnetic interaction is observed.

Calculation of the Electronic Density of States in Disordered Metallic Systems

AbstractThe use of N(E) = NFEk(∂E(k)/∂k)−1 as the electronic density of states for disordered metallic systems is critically examined. The present examination shows that its use is reasonable and that the applicability of the nearly‐free‐electron theory to the binary alloys of simple metals becomes worse and worse in going from the case of small charge transfer to the case of large charge transfer.

Ab-Initio Calojiations of Phase Diagrams of Binary Simplemetal Alloys

ABSTRACTThe combined application of electronic and thermodynamic perturbation theories allows for an ab-initio calculation of the phase diagrams of binary simple-metal alloys.

On the anomalous temperature dependence of the electrical resistivity in liquid alloys

It is demonstrated that the anomalous temperature dependence of the electrical resistivity, as experimentally reported for liquid binary alloys of simple metals, arises primarily from the significant decrease in the partial localization of the valence electrons on the electronegative component.

ELECTRONIC TRANSPORT IN LIQUID LITHIUM-LEAD ALLOYS

The self-consistent pseudopotential theory, developed previously for the binary alloys of simple metals, is applied to calculate (1) the excess electronic charges on the electronegative ions, i.e. Pb ions, due to the partial localization of the valence electrons on these ions and (2) the transport coefficients for the liquid Li-Pb alloy at different concentrations. It is found from this calculation that the partial localization of the valence electrons on the Pb ions in the Li-Pb alloy changes rapidly in going from the lowest concentration to the high concentration of Pb so that the transport coefficients of this alloy are strongly concentration dependeqt, as demonstrated in experiment. In addition, an improvement over the present type calculation is suggested.

A self-consistent pseudopotential applied to transport coefficients of liquid binary alloys of alkali metals

The energy-independent model pseudopotential theory, developed and used previously for simple metals, is extended to the binary alloys of these simple metals and a self-consistent pseudopotential, which contains a detailed concentration dependence, is derived for the calculation of various properties of these alloys. This pseudopotential is applied within a low-order perturbation theory to calculate the form factors and transport coefficients for the K-Rb, Na-K and Na-Cs alloys in the liquid state. The calculated results show that a very significant fraction of the valence electrons is localised on the electronegative component in the liquid Na-Cs alloy, as compared with the other alloys considered, and, as a result, the electrical resistivity is very much greater for the liquid Na-Cs alloy than for the liquid Na-K and K-Rb alloys, as demonstrated in experiment. Finally, the applicability of the pseudopotential perturbation theory to the liquid alloys of simple metals is discussed.

Electronic States of the Dilute Transiation Metal–Simple Metal Alloy According to the Resonant Model Potential Method

AbstractThe transition metal–simple metal alloy problem is formulated in the framework of the resonant model potential theory. It is reduced to a formally equivalent problem involving a tight‐bindinglike Hamiltonian, with non‐hermitian and energy dependent matrix elements. The s–d hybridization potential is exactly described by this non‐hermiticity. The Friedel‐Anderson virtual bound state (VBS) is recovered in the dilute limit. The theory is then applied to the 3d‐transition impurities in aluminium and the results are compared with observed values of the VBS widths.