X-ray investigation of short-range order in the liquid eutectic alloy Bi-Cd-Sn

From an analysis of the curves of the intensity of x-ray scattering and the atomic radial distribution function, information has been obtained about the formation of a complex polystructure in a liquid Bi-Cd-Sn melt near the melting point. The hypothesis is proposed that in the most probable structure of the liquid eutectic Bi-Cd-Sn alloy, in the neighborhood of the melting point, there are microscopic orbital regions containing bismuth atoms and microscopic regions with a statistical distribution of cadmium and tin. As the temperature is raised, this atomic distribution changes, and a homogeneous atomic solution is formed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 7–10, March, 1975.     

Close order in Ag-Ge liquid alloy of eutectic concentration

This paper gives results of the x-ray analysis of a eutectic Ag-Ge melt at temperatures of 655, 670, 685, 710, and 750 C. The intensity curves in copper radiation are obtained and the radial distribution curves of the atoms are calculated. It is established that a eutectic Ag-Ge melt in the range of temperatures under investigation may be described by a model of the statistical distribution of the atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 68–71, July, 1973.     

Atomic structure of melts of complex systems with eutectic transformations

The short-range-order structure of complex eutectic In-Sb-Sn, In-Sb, and Al-Sb-Bi melts is examined. The investigations are carried out on a high-temperature x-ray diffractometer. The curves of intensity of coherent x-ray scattering are used to plot the radial atom distribution functions (RADF). The RADF are analyzed for various different models of the structure of the fluids under investigation. It is established that the most acceptable model for the structure of In-Sb-Sn melts is the complex quasieutectic distribution corresponding to atom coordination in fused InSb and in fluid In and Sb. In a eutectic alloy of the Th-Sb system there are microinhomogeneous regions enriched with InSb atom complexes and with pure antimony in the total fusion region. A doped type of structure is characteristic of the Al-Sb-Bi melt. As the temperature rises the melts under investigation have a tendency to form a homogeneous solution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 88–92, July, 1976.     

Al-Zn-Mg-Cu-Li合金时效过程微结构演化的小角x射线散射研究

应用小角x射线散射技术分析了Al-Zn-Mg-Cu-Li合金在130，150和160℃温度时效24 h析出粒子的微结构参数的变化情况. 粒子的半径随着时效温度的增高而增加，它的比内表面积和体积百分数随着时效温度的增高而减小. 对Porod曲线q³J(q)-q²的分析表明,析出粒子与基体之间有明显的界面. 关键词： 小角x射线散射 Al-Zn-Mg-Cu-Li合金 时效 析出粒子     

Atomic-scale surface demixing in a eutectic liquid BiSn alloy

Resonant x-ray reflectivity of the surface of the liquid phase of the Bi(43)Sn(57) eutectic alloy reveals atomic-scale demixing extending over three near-surface atomic layers. Because of the absence of an underlying atomic lattice which typically defines adsorption in crystalline alloys, studies of adsorption in liquid alloys provide unique insight on interatomic interactions at the surface. The observed composition modulation could be accounted for quantitatively by the Defay-Prigogine and Strohl-King multilayer extensions of the single-layer Gibbs model, revealing a near-surface domination of the attractive Bi-Sn interaction over the entropy.     

Grain size and its distribution in NiTi thin films sputter-deposited on heated substrates

Grain size and its distribution in NiTi thin films sputter-deposited on a heated substrate have been investigated using the small angle x-ray scattering technique. The crystalline particles have a small size and are distributed over a small range of sizes for the films grown at substrate temperatures 370 and 420℃. The results show that the sizes of crystalline particles are about the same. From the x-ray diffraction profiles, the sizes of crystalline particles obtained were 2.40nm and 2.81nm at substrate temperatures of 350 and 420℃, respectively. The morphology of NiTi thin films deposited at different substrate temperatures has been studied by atomic force microscopy. The root mean square roughness calculated for the film deposited at ambient temperature and 420℃ are 1.42 and 2.75nm, respectively.     

Self-consistent interpretation of the 2D structure of the liquid Au82Si18 surface: bending rigidity and the Debye-Waller effect

The structural and mechanical properties of 2D crystalline surface phases that form at the surface of liquid eutectic Au82Si18 are studied using synchrotron x-ray scattering over a large temperature range. In the vicinity of the eutectic temperature the surface consists of a 2D atomic bilayer crystalline phase that transforms into a 2D monolayer crystalline phase during heating. The latter phase eventually melts into a liquidlike surface on further heating. We demonstrate that the short wavelength capillary wave fluctuations are suppressed due to the bending rigidity of 2D crystalline phases. The corresponding reduction in the Debye-Waller factor allows for measured reflectivity to be explained in terms of an electron density profile that is consistent with the 2D surface crystals.     

Über die Interpretation der Röntgenbeugungsdiagramme von mehrkomponentigen Schmelzen

The final results of x-ray diffraction experiments in molten alloys are electron distribution curves. These are used to get a decision between statistical distribution of the atoms of different kinds in the melt, between ordering of the atoms or between segregation. The according equations are deduced and finally a simple graphical method for the evaluation of the results is given. Important fact for the evaluation of molten alloys with a great difference between the atomic numbers of the two components is the number of scattering electrons in the first coordination sphere. With molten alloys which show little difference between the atomic numbers of the components the radius of the first coordination sphere is deciding. Finally it is shown, that the short range order parameter, which until now only was used in regard to the ordering in solid solutions, also can be used to get valuable results of the degree of ordering in molten alloys.     

Character of atomic short-range order in the V–Rh system

A study of atomic short-range order in a V-7 at. % Rh alloy was made, using the method of diffuse x-ray scattering and the pseudopotential method. Fluorescent radiation was excluded by using aluminum weakening foils and deducting the fraction of scattered radiation of pure vanadium. In the V-7 at. % Rh alloy, the existence was established of atomic short-range order in which neighboring atoms were primarily of opposite types.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 85–88, April, 1978.     

Structure of the ternary gallium-indium-tin eutectic system in the liquid state

An x-ray study has been made of the short-range structure of the ternary gallium-indium-tin eutectic system in the liquid state at T = 288, 308, and 368 °K. Intensity curves were compared with the diffraction reflections of the components. The radial distribution of atoms was calculated. This distribution is interpreted for model quasieutectic and statistical distributions of the scattering atoms. Near the melting point, the distribution of In, Ga, and Sn atoms in the alloy consisting of 62% Ga, 25% In, and 13% Sn (by weight) is quasieutectic, and a transition occurs to a homogeneous physical solution as the temperature is increased.Translated from Izvestiya VUZ. Fizika, No. 10, pp. 22–25, October, 1969.     

Study of nano-scale diffusion in thin films and multilayers

It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be used to study atomic diffusion with an accuracy of a fraction of a nanometer. Both the techniques can be made isotope selective by making use of nuclear resonance scattering from a Mössbauer active isotope. The techniques have been used to study self-diffusion of Fe in amorphous and nano-crystalline alloys of FeZr and FeN. The observed correlation of the activation energy E with pre-exponent factor D₀ confirms that in amorphous FeZr alloy diffusion takes place via collective motion of a group of atoms. Even in nanocrystalline alloys it is found that atomic diffusion occurs mainly through grain boundaries which are amorphous or highly disordered in nature.     

Pairing interactions and Gibbs adsorption at the liquid bi-in surface: a resonant X-ray reflectivity study

Resonant x-ray reflectivity measurements from the surface of liquid Bi(22)In(78) find only a modest surface Bi enhancement, with 35 at. % Bi in the first atomic layer. This is in contrast to the Gibbs adsorption in all liquid alloys studied to date, which show surface segregation of a complete monolayer of the low surface tension component. This suggests that surface adsorption in Bi-In is dominated by attractive interactions that increase the number of Bi-In neighbors at the surface. These are the first measurements in which resonant x-ray scattering has been used to quantify compositional changes induced at a liquid alloy surface.     

Ab initio calculations of the forbidden Bragg reflections energy spectra in wurtzites versus temperature

Thermal-motion induced (TMI) scattering is caused by the influence of atomic displacements on electronic states in crystals and strongly depends on temperature. It corresponds to dipole-dipole resonant x-ray scattering, but is usually accompanied by dipole-quadrupole scattering. The phenomenological theory supposes the dipole-quadrupole term to be temperature independent (TI). As a result, the transformation of the energy spectra with temperature observed experimentally in ZnO and GaN corresponds to the interference between the TMI and TI terms. In the present paper the direct confirmation of this theoretical prediction is given. Ab initio molecular dynamics was used to simulate the sets of atomic sites at various temperatures followed by quantum mechanical calculation of resonant Bragg reflection energy spectra. The results of simulation are in excellent coincidence with experimental energy spectra of forbidden reflections and confirm the earlier phenomenological conjecture about the interference between the TI dipole-quadrupole and TMI dipole-dipole contributions to the resonant atomic factor.     

Phase segregation and crystallization in the amorphous alloy Ni70Mo10P20

Structural evolution of the amorphous alloy Ni₇₀Mo₁₀P₂₀ has been studied by x-ray diffraction, and by following transmission and high-resolution electron microscopy annealing both above and below the glass-transition temperature. When annealed above this temperature, the amorphous phase undergoes segregation into regions about 100 nm in size having different chemical composition. Diffraction from such samples produces diffuse rings, and the scattering vector corresponding to the maximum intensity varies from point to point within the interval of 4.88 to 4.78 nm⁻¹. When occurring between the glass-transition and crystallization temperatures, crystallization produces groups of nanocrystals, 20–30 nm in size, which are in direct contact with one another and form a polymorphic mechanism. The crystallization mechanism changes when the annealing temperature is brought below the glass-transition point. At these temperatures the amorphous matrix crystallizes entectically with formation of eutectic colonies. Fiz. Tverd. Tela (St. Petersburg) 40, 1577–1580 (September 1998)     

Effects in the interphase boundary with contact melting in three-component systems

The crystallized, contact melting zone of binary eutectic alloys with a third eutectic component is investigated by an x-ray micrography method. Two layers are formed in the zone; one layer is liquid and the other, adjacent to the alloy, is solid-liquid. The dependence of the thickness of the layers on temperature and contact time is studied.     

Copper coordination hypotheses and atomic arrangement in the glassy alloy Cu0.25As0.30Te0.45

Summary The radial atomic distribution of the amorphous alloy Cu_0.25As_0.30Te_0.45 was studied, through the X-ray diffraction data supplied by samples obtained through quenching. The short-range order was determined by interpreting the radial distribution function (RDF), using a theoretical expression which takes into account the variation in the atomic scattering factors withs (the scattering vector module), and approximates them to polynomic functions. The tetracoordinated copper hypothesis, quoted in the literature for glassy alloys containing this element, was considered. The result of the study is that, for the alloy in question, the tetracoordinated copper hypothesis is compatible with the structural information that was experimentally obtained. A spatial atomic distribution model was generated according to this copper coordination, using the conveniently modified Monte Carlo random method. A comparative analysis of the main structural parameters of this model revealed their good agreement with the values given in the literature for similar alloys.     

Structure characterization and mechanism of growth of PbTe nanocrystals embedded in a silicate glass

A nanocomposite consisting of PbTe nanocrystals embedded in a silicate glass was studied by small-angle x-ray scattering during the early stage of isothermal annealing at 793 K. A theoretical function based on a model of spherical PbTe nanocrystals surrounded by a Pb and Te depleted shell fits well to all experimental curves. The time dependences of the nanocrystal radius and size of the depleted shell agree with the prediction of the theory of nucleation and growth by the classical mechanism of atomic diffusion.     

Local-order hypotheses and atomic arrangement in the glassy alloy As0.45Se0.05Te0.50 by X-ray diffraction

Summary The radial atomic distribution of the amorphous alloy As_0.45Se_0.05Te_0.50 was studied through the X-ray diffraction data supplied by samples obtained through quenching. The short-range order was determined by interpreting the radial distribution function (RDF), using a theoretical expression which takes into account the variation in the atomic scattering factors withs (the scattering vector module), and approximates them to polynomic functions. The tetra- and tri-coordinated arsenic hypotheses, quoted in the literature for glassy alloys containing this element, were considered. The result of the study is that, for the alloy in question, only the tri-coordinated arsenic hypothesis is compatible with the structural information that was experimentally obtained. A spatial atomic distribution model was generated according to this arsenic coordination, using the conveniently modified Monte Carlo random method. The model is a network of triangular pyramids with arsenic atoms at some vertices. A comparative analysis of the main structural parameters of this model revealed their good agreement with the values given in the literature for similar alloys.     

Deep inelastic atomic scattering of x rays in liquid neon

An inelastic x-ray scattering (IXS) experiment in liquid neon has been performed in the +/-100 meV exchanged energy range and at exchanged wave numbers, q, comprised between 1 and 16 A(-1). At the highest probed q's a deep inelastic scattering regime is reached where the Ne core electrons, after collision with the x rays, recoil almost freely with an effective mass equal to the Ne atomic mass. IXS in this high q regime is here shown to provide quantitative information on the atomic momentum distribution of liquid Ne, thus supplying a complementary technique to neutron scattering. There are several open problems in quantum and classical liquids which can benefit from this complementarity.     

Positive vibrational entropy of chemical ordering in FeV

Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to measure phonon spectra of FeV as a B2 ordered compound and as a bcc solid solution. The two data sets were combined to give an accurate phonon density of states, and the phonon partial densities of states for V and Fe atoms. Contrary to the behavior of ordering alloys studied to date, the phonons in the B2 ordered phase are softer than in the solid solution. Ordering increases the vibrational entropy by +0.22±0.03 kB/atom, which stabilizes the ordered phase to higher temperatures. First-principles calculations show that the number of electronic states at the Fermi level increases upon ordering, enhancing the screening between ions, and reducing the interatomic force constants. The effect of screening is larger at the V atomic sites than at the Fe atomic sites.