Li-Mg Alloys Research Articles

A first principles study on the structure and the elastic properties of Li-Mg alloys

Elastic properties of the Li15Mg alloy have been studied by using the first principles structural optimization method. The results show that at zero pressure the relative distance between the Mg atom and the nearest Li atoms is larger than that in the ideal crystal and when compressing the lattice this distance will increase further. A simple model is introduced to interpret this relaxation. It is also shown that structural optimization has to be taken into account when investigating the bulk properties of alloys. The bulk modulus of the optimized Li15Mg is smaller than that of the ideal structure although the volume of the optimized structure is smaller than the volume of the ideal structure. Hence bulk modulus is determined not only by change in the crystal volume but also by local changes in the crystal structure near to the Mg atom. An interpolation formula to calculate compressibility at any composition is presented.

The Electron Momentum Distribution of LiMg Alloys by Positron-Annihilation 2D-ACAR

The Electron Momentum Distribution of LiMg Alloys by Positron-Annihilation 2D-ACAR

Very-low-temperature electrical resistivity of KRb, KNa, and LiMg alloys.

Previous high-precision measurements below 0.5 K showing a resistivity anomaly in KRb and dilute KNa and LiMg alloys have been extended to KNa and LiMg alloy samples which cover the residual-resistivity range from ${\ensuremath{\rho}}_{0}$=4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ to 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ \ensuremath{\Omega} m. Residual-resistivity data per atomic percent impurity are consistent for all three alloys with literature results in the regions of overlap. The data for all three alloys also show the expected behavior for inelastic electron-impurity scattering. At temperatures above 1 K, the KRb and KNa alloy data show increases in electron-phonon scattering with increasing ${\ensuremath{\rho}}_{0}$ probably due to quenching of phonon drag and---for KRb---to reduction in the Debye temperatures of the alloys. All three alloy systems display a low-temperature anomaly which has a universal magnitude for a given ${\ensuremath{\rho}}_{0}$ when ${\ensuremath{\rho}}_{0}$${<10}^{\mathrm{\ensuremath{-}}7}$ \ensuremath{\Omega} m, and which varies approximately linearly with both temperature and residual resistivity. Localization, electron-electron interaction, and Kondo effects appear to be ruled out as explanations for the anomaly in this regime. Published models based on charge-density waves and ineffectiveness of electron-phonon scattering are also considered. As ${\ensuremath{\rho}}_{0}$ increases above ${10}^{\mathrm{\ensuremath{-}}7}$ \ensuremath{\Omega} m, the anomalous behavior approaches the electron-electron interaction limit. In the very-high-concentration LiMg alloys microscopic differences between the alloys are found to affect the data.

Electronic structure and bonding in NaLi, LiMg and LiAl alloys: a MS Xα SCF approach

A MS Xα SCF method has been initiated to calculate the charge distribution, bonding properties and the density of states in NaLi, LiMg and LiAl alloys. No ionicity is seen in NaLi but a high covalency of different degree is detected in all the three alloys. The ionizations potentials calculated are 5.05, 5.5 and 5.58 eV respectively. Comparison with other calculations and experiments is found to be in fair agreement.

Electrochemical study of mass transfer in Li-Mg and Li-Mg-Al alloys

The interdiffusion coefficients in Li-Mg alloys and Li-Mg-Al alloys were evaluated using transient techniques such as chronopotentiometry and chronoamperometry. Anodic or cathodic pulses were imposed on the alloy electrodes under galvanostatic and potentiostatic conditions.

Low Temperature Resistivity Anomalies in Concentrated LiMg Alloys

Previous measurements showing a resistivity anomaly in KRb and dilute KNa and LiMg alloys have been extended to more concentrated LiMg alloys. The anomaly is found to approach the electron-electron interaction limit when the residual resistivity ρo becomes greater than about 100 nΩm. In the most concentrated alloys, the anomalies show large variations when the sample heat treatment is changed. This behavior suggests that microscopic differences within these alloys affect the data.

Electron-electron scattering in Li

Measurements of the electrical resistivity of pure Li and LiMg alloys below 3K indicate that the magnitude of electron-electron scattering in pure Li is determined directly by the band structure of Li rather than indirectly by anisotropic scattering.

Low-temperature deviations from Matthiessen's rule in lithium-magnesium alloys

The resistivity of lithium and three LiMg alloys with magnesium concentrations of 1.0, 5.0 and 10 at.% has been measured from 2 to 60K. Below 10K a term proportional to T2 and to the residual resistivity is identified and associated with inelastic impurity scattering of electrons. At higher temperatures the deviations from Matthiessen's rule are found to become essentially independent of concentration.

Simple model for the structure and thermodynamics of liquid alloys with strong chemical interactions. I. Chemical short-range order

The authors present a simple model for the structure and thermodynamics of liquid alloys with strong chemical interactions. Starting from the fact that these systems are characterised by the existence of a non-vanishing ordering potential phi CC=c1c2( phi 11+ phi 22-2 phi 12), the authors model the interatomic potentials by a hard-sphere potential for the mean pair interaction phi NN=c12 phi 11+c22 phi 22+2c1c2 phi 12 and a hard-sphere potential of the same diameter plus a Yukawa tail for phi CC. The volume forces are calculated in an electron-gas model. Based on the solution of this model in the mean spherical approximation, the authors find analytic expressions for the thermodynamic excess functions and the partial structure factors. They have applied their model to liquid Li-Pb, Li-Ag and Li-Mg alloys and find very good results for the heat and the entropy of formation and good agreement between their structure data and neutron scattering experiments.

7Li Knight shift in liquid Li-Mg alloys

The 7Li Knight shift in liquid Li-Mg alloys is found to be a linear, decreasing function of the magnesium concentration. This result is explained qualitatively in terms of transfer of Fermi electrons from the Li to the Mg cells, in agreement with calculations of the local density of states in solid LiMg by Inglesfield. The Korringa enhancement increases monotonically when magnesium is added to lithium.

Effects of the Tahir-Kheli,Intermediate-Temperature Teriis on the Clapp and Moss, High–Temperature Formulation of Short Range Order (Sro) in Li-Mg Alloys

ABSTRACTPresent calculations of the Cowley-Warren SRO parameters, using the Rasolt-Taylor-Dagens, first principles pair potential for Li-Mg alloys show that the higher order terms of Tahir-Keli's intermediate-temperature solution of the Ising, spin-1/2 ferromagnet modify the Clapp and Moss, hightemperature solution in a very significant way. The present results are compared to previous calculations and measurements on Li-10 at.% Mg and Li-50 at.%Mg alloys.

DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF LITHIUM-MAGNESIUM ALLOYS

DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF LITHIUM-MAGNESIUM ALLOYS

X‐ray compton scattering from LiMg alloys

AbstractResults are given of X‐ray Compton scattering from a series of LiMg alloys, polycrystalline Li, and Mg. The spectra indicate a contact of the “Fermi surface” of the alloy with the [110]‐Brillouin zone boundary at 30 to 40 at % Mg. LiMg seems to be a good, nearly free electron alloy. Theoretical calculations using a model alloy potential are made and the calculated momentum distributions are compared with the experimetnal results.

Electromotive Force Measurements in Molten Lithium‐Magnesium Alloys

not Available.

Positron localization in Li-Mg alloys

Positron-annihilation experiments have been performed on a number of disordered Li-Mg alloys, and information on the spatial distribution of annihilating positrons has been deduced. Measurements of the angular correlation of the two annihilation $\ensuremath{\gamma}$ rays and of the positron lifetime have been made and the results used to obtain core-annihilation rates. The core rate is sensitive to the distribution of the annihilating positrons between the two different sorts of sites in the alloy, and the results indicate that the positrons are sampling a much greater proportion of Li atoms in the alloy than the mean Li concentration would indicate. First-principles calculations of the positron distribution based on the positron pseudopotential are in qualitative agreement with the experimental results but do not include effects of localization. Smearing of the Fermi cutoff region of the angular correlation curve can be a measure of positron localization. Experimental results for the smearing for the dilute Li alloys indicate that the annihilating positron is localized in a region extending roughly 20 \AA{}. It is concluded that the positron is annihilating from bound states localized to Li-rich regions of the alloy. These results are important in the interpretation of positron-annihilation experiments in disordered alloys and also in the understanding of low-lying electron states in disordered alloys.

Lattice parameters of lithium-magnesium and lithium-silver alloys

The lattice parameters of solid solutions of magnesium and silver in lithium have been measured by X-ray diffraction, using extruded wire specimens. The results for the LiMg alloys are compared with some previously published values. In the dilute (<0.5 at%Ag)LiAg alloys, a very rapid change in the lattice parameter of -1.7 * 10-2 angstrom per at % Ag was found.

The optical properties of lithium-manganese alloys

A series of LiMg alloys has been studied by ultra high vacuum ellipsometry. The b.c.c. alloys containing more than 30% Mg show pronounced parallel band absorption and values of the energy gap at the (110) zone boundary are accurately derived. The optical properties of these concentrated disordered alloys show convincingly that the concepts of Fermi surface and zone structure maintain their significance in such disordered systems. The optical and soft X-ray data for Li are used to obtain a qualitative description of the band structure of this metal. The virtual crystal model is applied to the alloy data and found to give a rather poor description of the observed behaviour.

The Hall Coefficients of Li-Mg Alloys

The temperature and concentration dependences of the Hall coefficients in β-phase of lithium-magnesium alloys (0∼70 at.%Mg) have been measured from 77°K to the room temperature. In the temperature range investigated, Hall coefficient is almost independent of the temperature except pure lithium. The dependence of Hall coefficient ( R H ) on electron-atom ratio (e/a) is approximately represented by a third-degree polynomial; R H ×10 11 (m 3 /A.s)=85.58(e/a) 3 -333.31(e/a) 2 +443.00(e/a)-210.80. Although there is fluctuation to some extent in the experimental data, a distinct agreement is found between the experimental results and the prediction by four-OPW calculation. For this reason, the four-OPW model is thought to be a good approximation for this alloy phase. The experimental result suggests the contact of the Fermi surface to the {110} zone boundary at e/a=1.3. The result also suggests that overlap through {110} zone face does not occur in the measured range.

Theory of mechanical relaxation due to changes in short-range order in alloys produced by stress (Zener relaxation)

Abstract A general expression for the relaxation strength Δ M for Zener relaxation is obtained in terms of the rates of change with strain of the short-range order parameters and of the assumed pair-wise interaction energies between atoms. A Bethe-Peierls description of the degree of order yielded values of Δ M in agreement with experiment (Le Claire and Lomer 1954) but is unable to explain more recent observations in a AgZn and LiMg alloys of (1) a marked anisotropy of Δ M (Seraphim and Nowick 1961) and (2) a positive critical temperature, increasing with solute concentration, in the Curie-Weiss type temperature dependence of Δ M (Li and Nowick 1961). Both these defects are fully remedied when the more complete Cowley (1950, 1960) equations are used to describe the degree of order. First and second nearest-neighbour interaction energies only need to be taken into account and order parameters out to eighth neighbours. Good agreement with experimental measurements on a AgZn alloys is obtained with a choice...

Remarks on the elastic constants and temperatures of martensitic transformation in the Li-Mg alloys

The correlation between the elastic constants and the martensitic transformation temperature is discussed. Data for the Li--Mg alloys are tabulated which show that the transformation occurs at higher temperatures as the elastic anisotropy increases with change in Mg content. (D.L.C.)