Role of magnetism in the formation of a short-range order in an Fe-Ga alloy

The formation of a short-range order in an Fe-Ga bcc alloy has been studied by Monte Carlo simulation with the use of effective interaction potentials calculated within the density functional theory for the ferromagnetic and paramagnetic states. It has been found that the pronounced short-range order of the D0₃ type is formed at Ga concentrations close to the boundary of the two-phase region at T < T _c, whereas no short-range order is observed at T < T _c. The results obtained are in agreement with the experimental X-ray diffraction analysis. The relation of the features of the short-range order in the Fe-Ga alloy to the magnetostriction value has been discussed.     

Atomic short-range order in CuMn alloys

The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change.     

Icosahedral short-range order in amorphous alloys

We have characterized the icosahedral short-range order in amorphous solids using local environment probes. Such topological local order is pronounced even in an amorphous alloy that does not form quasicrystalline phases upon crystallization, as demonstrated by the extended x-ray absorption fine structure and x-ray absorption near-edge structure of a Ni-Ag amorphous alloy analyzed through reverse Monte Carlo simulations.     

Influence of the local environment and short-range order on the heats of formation of binary alloys

The concentration dependences of the heats of formation (H(x)) of disordered binary alloys of iron and cobalt with titanium have been calculated in both the single-site approximation and with allowance for the local environment. The dependence of H of equiatomic alloys on the short-range order in the first coordination sphere is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 62–66, August, 1980.     

Concentration dependence of short-range order parameters in annealed copper-aluminum alloys

The method of diffuse X-ray scattering was used to investigate -CuAl alloys containing between 11.9 and 17.6 at.% aluminum after prolonged stepwise annealing. Analysis of the short-range order coefficients indicated uniform ordering at concentrations up to 15 at.% aluminum and possible departure from uniform ordering in alloys with higher concentrations. It was shown that the structure of the ordered alloy is consistent with the model proposed by Gehlen and Cohen [13].     

New theory of binary alloys with short-range order properties

A new method for treating the electronic structure of binary alloys is presented. It is based on the study of a finite size cluster connected at its edges to a Bethe-lattice of the same coordination number. An illustrative example is presented. It includes concentration sequences which are (i) random, (ii) with a tendency to segregation and (iii) with a tendancy to form binary compounds. Energy gaps and localized states appear naturally in the method.     

Effect of short-range order on thermo-emf of binary alloys

The thermo-emf of binary disordered alloys is calculated, taking into account correlations in the distribution of atoms of different kinds over the lattice. It is shown that the presence of short-range order in the alloys may lead to a nonlinear temperature dependence of the thermo-emf and cause a change in its sign.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 87–91, November, 1976.     

Dislocations in crystals of iron-silicon alloys indented by a ball

Slip bands inside the area deformed by the indentation of a steel ball are studied by the method of making dislocations visible by etching on the surfaces of iron-silicon alloys. The shape of the slip surfaces is examined and the dimensions of the deformed area as a function of the silicon content, of the temperature and of the deformation speed are determined. The observed slip is microphysically explained assuming that parts of the screw dislocations, if moving, show a cross-slip.     

Influence of short-range atomic order on nuclear magnetic resonance in liquid alloys

N.M.R. Knight shift and line width variations of ¹¹⁵In and ²⁰⁹Bi in In-Bi liquid alloys, as a function of temperature and field, are interpreted as showing that InBi and In₂Bi atomic groupings persist in the liquid state. An activation energy for the dissociation of InBi groupings of 2 kcal mole^?1 is deduced from the temperature dependence of an excess line width observed at 50% Bi. The lifetime of this species is found to be 4×10^?7 sec at 580°k from the magnitude of a field dependent broadening observed at concentrations between 50 and 100% Bi. Qualitative evidence for the existence of In₂Bi groupings is obtained from the Knight shift data. It is suggested that this type of measurement may be applicable to other liquid alloys and should provide a method at least as sensitive as resistivity and viscosity measurements for the detection of preferred atomic groupings.     

Influence of interatomic correlation effects on short-range order in hexagonal close-packed polycrystalline alloys

The first x-ray diffraction procedure suitable for the investigation of short-range order in polycrystalline alloys having a hexagonal close-packed (hcp) lattice is developed on the basis of the theory proposed by M. A. Krivoglaz for diffuse x-ray scattering by hcp single-crystal alloys. This procedure takes into account specific details of the crystal structure of the hcp lattice, in particular, the presence of two atoms in the unit cell and the close radii of the individual coordination spheres. The realistic character of the procedure is demonstrated experimentally in the example of hcp Mg-Dy and Mg-Tb alloys. The new procedure is used to calculate, for the first time, the modulating functions of linear and quadratic size effects in Mg-Dy and Mg-Tb alloys. It is shown that the size-effect modulating functions for coordination spheres with close radii have different characters, and their inclusion in diffuse scattering sets the stage for solving the problem of calculating the short-range order parameters on these spheres. Fiz. Tverd. Tela (St. Petersburg) 41, 2109–2115 (December 1999)     

Effect of short-range order on the band-edge behavior of the electronic spectrum of disordered alloys

The electronic spectrum of a one-dimentional disordered alloy was calculated both analytically and numerically for energies close to a band edge. The density of states is shown to be strongly dependent on the presence of short-range order in the form of correlations between the occupancies of neighboring sites.     

Effect of short-range order on electronic and magnetic properties of disordered Co-based alloys

We here study electronic structure and magnetic properties of disordered CoPd and CoPt alloys using augmented space recursion technique coupled with the tight-binding linearized muffin tin orbital (TB-LMTO) method. Effect of short-range ordering present in disordered phase of alloys on electronic and magnetic properties has been discussed. We present results for magnetic moments, Curie temperatures and electronic band energies with varying degrees of short-range order for different concentrations of Co and try to understand and compare the magnetic properties and ordering phenomena in these systems.