Calculation of the properties and the structure of ordering alloys of the Cu—Au system

The observed phase diagrams of noble-metal alloys demonstrate that the nature of alloy formation differs widely. The ordered phases Cu3Au, CuAu, and CuAu3 form in the Cu-Au system as the temperature decreases. Alloys of the Cu-Ag system in the solid state have a tendency to separate while a continuous series of solid solutions is formed in the Ag-Au system. With the large volume of experimental information and theoretical phase stability calculations for those systems, a detailed comparative analysis can be made with the results obtained using new theoretical models. Structural analysis of the alloys of the systems studied is fairly straightforward since the experimentally observed ordered phases have a cubic symmetry (Llo, Llz) and the disordered phases form solid solutions based on the fcc lattice. Furthermore~ the existence of a tetragonal distortion in the CuAu alloy in the Llo structure is of particular interest.Earlier, in [1] we proposed the model electron-density functional (MEDF) method, which can be used to calculate the total energy of alloys with allowance for many-body interatomic interactions. In the work reported here we use the MEDF method to investigate the ground state of noble-metal alloys and to analyze the factors responsible for the tetragonal distortion of the L10 structure on the basis of a proposed model of the binding forces of metallic systems.In the MEDF method the electron density in a crystal is represented as the superposition of the core-electron and almost-free-electron densities pc(r) and p jr). The electrons of inner filled shells and valence d electrons are core electrons and s and p electrons are in the almost-free category. With this division of the densities the total energy E[p] of the alloy has the formwhere El [Pc] is the core-electron energy, which (as in the binding-force method) includes the Coulomb, kinetic, and exchange energy of the core electrons, E2Lov] is the energy of the almost-free electrons, and E3[p c, pv] is the energy of the interaction between the systems of core and almost-free electrons. The electron density of core and almost-free electrons in the crystal is represented as the sum of spherically symmetric densities p~ and p? of species ~ atoms. Thus for p~(r) we have

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Interatomic Interaction in Transition and Noble Metal Alloys and the Stability of the Ordered State

Dementyev¹,

Козлов²,

Kolodeznaya³

1984

MRS Proc.

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The nature and the role of the pair interatomic interaction of the noble and transition metal ordering alloys are considered. The determining role in the electron susceptibility in the behaviour of the interatomic interaction is shown. The important role of the Fermi surface local geometry in the definition of superstructure periods is established. Illustrating calculations are made. It is shown that in the noble and transition metal alloys with complicated Fermi surface the oscillations of the pair interatomic interaction are of essentially nonfriedel character.

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Calculation of the properties and the structure of ordering alloys of the Cu—Au system

Cited by 3 publications

References 14 publications

Thermodynamic properties of noble-metal alloys using the cell approximation in the method of a model electron-density functional

Thermodynamic properties of noble-metal alloys using the cell approximation in the method of a model electron-density functional

Calculation of the thermodynamic properties of noble-metal alloys in the model electron-density functional method

Interatomic Interaction in Transition and Noble Metal Alloys and the Stability of the Ordered State

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