Anomalous X-ray diffraction from ω nanoparticles in β-Ti(Mo) single crystals

Anomalous X-ray diffraction (AXRD) is a technique which makes use of effects occurring near the energy of an absorption edge of an element present in the studied sample. The intensity of the diffracted radiation exhibits an anomalous decrease when the primary beam energy matches the energy needed to excite an electron from an atomic orbital. The characteristics of this step are sensitive to the concentration of the `anomalous' element and its spatial distribution in the sample. In the present investigation, AXRD was employed to study ω particles in a metastable β titanium alloy Ti–15Mo (in wt%). The experiments were done in an energy range around the Mo K edge at 20.0 keV, allowing investigation of the distribution of Mo in the material, which is rejected from the volume of ω particles during their diffusion-driven growth. This paper deals with diffuse scattering patterns around the (006)β diffraction maximum. It was observed that different regions of the diffuse scattering exhibited different variations of diffracted intensity with the incident photon energy near the absorption edge. Numerical simulations of diffuse scattering patterns as well as of energy dependences of the scattered intensity were performed. It was found that the observed patterns and their dependence on the primary beam energy can be explained by taking into account (a) elastic deformation of the β matrix arising from the presence of slightly misfitting ω particles and (b) the presence of a `cloud' of a higher Mo concentration around ω particles.

Самоорганизация разномасштабных структурных групп в малоуглеродистой проволоке под действием интенсивного волочения

The peculiarities of the mechanical parameters and atomic structure of wires made of 08G2S steel subjected to severe drawing with a combination of shear and classical circular drawing of different diameters. The split form of interference maximums (211) in X-ray diagrams of samples is evidence for delamination in families of the mentioned planes into contracted and extended groups, which is accompanied by the partial order–disorder phase transition with formation of the amorphized fraction from fragments of nanosized atomic groups of these planes (clusters). The dependence on steel deformation revealed the nature of the change in the symmetry of the distribution of structural groups relative to the angular position of the diffraction maximum from the planes (211). It is established that with increased deformation (ε > 30%) the intensities of coherent and incoherent X-ray Cr K _α-emissions vary quantitatively, which proves the development of self-organizing processes contributing to the increase in the volume fraction of the order relative to the disorder in 08G2S steel, even subject to severe mechanical loading.

On the completeness of the β→ω transformation in metastable β titanium alloys

The completeness of the β→ω transformation in ω particles in a Ti–8 at.%Mo (Ti–15 wt%Mo) single crystal was investigated by measuring the X-ray diffraction maximum 20{\overline 2}2, which is forbidden in both the pure body-centred cubic β phase and the hexagonal ω phase, and also the diffraction maxima 0001, 0002 and 10{\overline 1}1, which are forbidden in the β phase and allowed in ω. From a comparison of the integrated intensities and widths of the diffraction peaks with simulations, the effective (mean) degree of the transformation was determined and the radial profile of the transformation degree in an ω particle was estimated.

Structural Characterization of Heteroepitaxial Growth of AlxGa1-xSb/GaSb by LPE

The heteroepitaxial AlxGa1-xSb/GaSb (001) growth with different x aluminum content, from 0.05 to 0.2 prepared by Liquid Phase Epitaxy (LPE) is presented. The interest in this study is due to the layers of AlxGa1-xSb systems should be well matched for fabrication of sources and detectors operating in the 1.3-1.6 micron range. The layered structure obtained was characterized mainly by high-resolution X-ray diffraction and reciprocal space mapping. In the case of x = 0.05 aluminum content, the relaxation is minimal, and almost without deviation respect to GaSb. As the aluminum content increases above 0.05, the relaxation is larger and deviation from GaSb substrate too. Crystallographic tilt is detected by a shift of layer diffraction maximum on reciprocal space maps. Deviation changes the intensity of layer respect to substrate peak in rocking curves and hence the estimation of thickness of layer obtained from them. A correction for estimated thickness of layers is obtained from mapping.

Computer models of icosahedral carbon nanostructures (shungite)

A universal algorithm for the generation of three-dimensional models of icosahedral fullerene-like carbon nanostructures has been developed. Coordinates of atoms on their surface are calculated and three-dimensional models of fulleroids – nested icosahedra – are built. A flat model consisting of five graphite layers of varying diameters is computed in an attempt to explain the nature of the diffraction maximum (d≃ 6.81 Å, 2θ ≃ 13°) in shungite carbon by the existence of edge effects, carbon atoms or small fragments of layers in the interlayer space, or dislocation rings.

Structural modifications of smectites mechanically deformed under controlled conditions

SWy-1 and SAz-1 smectites and an Italian bentonite from Sardinia were mechanically deformed via high-energy ball milling for 20 h, in a controlled thermodynamic environment at constant temperature (25°C) under vacuum. The deformed smectites have a lower cation exchange capacity (CEC) and form thicker particles than the original ones, due to agglomeration of smectite crystallites. The 001 diffraction maximum shifted to lower d spacings, the intensity of the 060 reflection decreased and the background at 20-30°2θ increased, suggesting partial amorphization of the smectite. Moreover, the layer charge of the smectites decreased. The intensity of the complex stretching band at 3625 cm-1, and the AlAlOH, and AlFe3+OH bending bands at 916 cm-1 and 886 cm-1, respectively, decreased, while the band at AlMgOH bending at 849 cm-1, disappeared. Deformation mainly disrupted the octahedral sheet and preferentially destroyed those sites occupied by Mg cations, thus explaining the observed decrease in layer charge. Octahedral sites occupied by Fe were least affected. The disruption of the octahedral sheet is substantiated further by the almost total disappearance of the dehydroxylation peak, which is more pronounced in the Mg-rich SAz-1 smectite.

A new interpretation of reduction in absorption coefficient at and near Laue diffraction maximum in thin and perfect crystals on the basis of dynamical theory of X-ray diffraction

By analysing in detail the existing plane wave dynamical theory of X-ray diffraction for thin (

Modeling of Neutron Diffraction Patterns from Sheared Silica Gels

ABSTRACTDense silica gels, prepared from suspensions of 24 nm colloidal silica particles, have been studied by small angle neutron scattering. Provided the volume fraction, φ, of the silica is less than about 0.18, the scattered intensity increases at low wavevector, q, as the gelation proceeds and the structure factor, S(q), of the final gel exhibits apparent power law behavior, usually interpreted as a signature of fractal growth. The power law behavior, however, was observed for all measured φ (≤0.30) when the gelation occurred in the presence of an applied shear. Furthermore, the first diffraction maximum, corresponding to the inter-particle contact distance, was more sharply peaked in the high density sheared gels, indicating that the structural arrangement of the silica particles under shear is more densely packed than in gels produced without shear under equivalent conditions. Although it is clear that shear has a marked influence on the gel structure at higher densities, a quantitative interpretation of the diffraction results is difficult because cluster-cluster interference might be present. Such difficulties encountered when trying to interpret the scattering from these dense systems are outlined, and a computer simulation that includes cluster-cluster interference is presented.