Resonant diffraction of synchrotron radiation: New possibilities

Resonant diffraction of synchrotron radiation (SR) is a modern method of studying the structure and properties of condensed matter that can be implemented on third-generation synchrotrons. This method allows one to investigate local properties of media (including magnetic and electronic ones) and observe thermal vibrations, defects, and orbital and charge orderings. A brief review of the advance provided by SR resonant diffraction is presented, and the capabilities of this method for analyzing phase transitions are considered in more detail by the example of potassium dihydrogen phosphate and rubidium dihydrogen phosphate crystals. It is shown that the investigation of the temperature dependence of forbidden reflections not only makes it possible to observe the transition from para- to ferroelectric phase, but also gives information about the proton distribution at hydrogen bonds.     

Formation of photoelectron holograms of crystals excited by synchrotron radiation

The theoretical aspects of formation of photoelectron beams excited by the ultraviolet synchrotron radiation incident onto a crystal are considered. It is shown that the change in the energy of the monochromatized synchrotron radiation incident onto a hematite crystal results in the change of the number of reflections participating in the hologram formation.     

X-ray diffraction measurements for liquid Ge–Si alloys using synchrotron radiation

Energy dispersive X-ray diffraction measurements have been carried out for liquid Ge_1−xSi_x alloys (x = 0.0, 0.3, 0.5, 1.0) using synchrotron radiation at SPring-8. We measured the X-ray diffraction spectra of liquid Ge and Si up to a high temperature range, (liquid Ge from 1270 to1870 K and liquid Si from 1680 to 2020 K), liquid Ge_0.7Si_0.3 at 1620 K, and liquid Ge_0.5Si_0.5 at 1540, 1590, 1670 and 1720 K. The total structure factors of the liquid Ge–Si alloys have a characteristic shoulder on the high-wave-vector side of the first peak. We deduced a pair distribution function from the Fourier transform of the observed structure factor, which was weakly dependent on the temperature. The nearest-neighbor coordination number of liquid Ge–Si alloys is close to that of pure liquid Ge and Si. The first peak of the pair distribution function moved to a shorter distance with increasing Si concentration. These results may indicate that the atomic radii of the Si and Ge atoms in the pure liquid are preserved in the liquid alloys.     

Effect of strain in crystal on the forbidden reflections in the resonant diffraction of synchrotron radiation

The effect of strain (either static or caused by long-wavelength acoustic oscillations) on the energy spectrum and the azimuthal dependence of the intensity of “forbidden” reflections in crystals at the energy of incident radiation close to the absorption edge is considered. It is shown that a strain causing a weak change in the unit-cell symmetry may additionally contribute to the tensor atomic factor. Examples of changes in the azimuthal dependence of forbidden-reflection intensity in zinc oxide ZnO and potassium dihydrogen phosphate KH₂PO₄ are considered.     

X-ray diffraction measurement of liquid As2Se3 by using third-generation synchrotron radiation

X-ray diffraction (XD) measurements of liquid As₂Se₃ were carried out in the temperature range up to 1600 °C where the temperature is well beyond the semiconductor to metal (SC–M) transition temperature around 1000 °C. The measurements were done by using third-generation synchrotron radiation at SPring-8 and the obtained structure factors have been much improved compared to previous in house XD measurements with regard to the momentum transfer range and the data statistics. The deduced pair distribution functions show that with increasing temperature, the position of the first peak does not change within the errorbar and the coordination number gradually decreases up to 1600 °C irrespective of the SC–M transition. These results coincide with those of the first-principle molecular dynamics simulation.     

Study of the crystal device for deflecting high-energy proton beams using synchrotron radiation diffraction

Currently, bent silicon single crystals are used at large accelerators to extract and collimate proton beams. A device for multiple deflection of a proton beam based on several bent silicon strips operating in the volume reflection mode has recently been developed. In this device, the bending of silicon strips successively located on the surface of a thick plate is implemented due to the internal stress induced by grooves mechanically formed on the crystal surface (Twyman effect). Topography based on angular scanning and synchrotron radiation was applied to measure the bending of individual deflector strips and the crystal as a whole. The measurement results are compared with the data obtained with a proton beam.     

Numerical simulation of experimental resonance absorption spectra and diffraction of synchrotron radiation in yttrium iron garnet

Extended X-ray absorption fine-structure spectra of yttrium-iron garnet, measured near the absorption edges of iron and yttrium at the Kurchatov synchrotron radiation source are reported. Numerical simulation of the X-ray absorption near-edge structure of these spectra is performed and good agreement with the experimental data is obtained. It is shown theoretically that “forbidden” Bragg reflections can be observed near the absorption edges of iron and yttrium. The indices of these reflections are determined. The energy structure of the “forbidden” reflections 006 and 110 is calculated.     

Neutron diffraction and X-ray diffraction investigations of langasite crystals

Crystals of langasite La₃Ga₄(GaSi)O₁₄ grown by the Czochralski method are studied using neutron diffraction for the first time. It is established that the compositions of the upper and lower parts of an orange crystal grown from the La₃Ga_5.14Si_0.86O₁₄ seed in an (Ar + O₂) atmosphere (the 〈 0001 〉 growth direction) can be written as(La_2.85(2)□_0.15)(Ga_0.95(2)□_0.05) Ga₃(Ga_1.15 Si_0.85(5))(O_13.72□_0.28(7)) and(La_2.89(1)□_0.11)·(Ga_0.98(1)□_0.02) Ga₃(Ga_1.06Si_0.94(4))(O_13.81□_0.19(9)), respectively. The La content in the upper and lower parts of this crystal is lower and higher than the Ga content, respectively, and the Ga content exceeds the Si content in the (GaSi) position. By contrast, in a colorless crystal of the composition(La _2.97(4)□_0.03) Ga(1)(Ga_2.94(9)□_0.06)(Ga_0.7(1) Si_1.3)(O_13.9□_0.1(1)), which is grown from the La₃ Ga₅SiO₁₄ seed in an argon atmosphere (the 〈 01\(\bar 1\)1 ?growth direction), the Ga content in the (GaSi) position is lower than the Si content. A relation between the Ga: Si ratio and the (Ga,Si)-3O interatomic distances is found.     

Structural evolution of metallic glasses during annealing through in situ synchrotron X-ray diffraction

In this work we study the structural evolution of Al and Fe based metallic glass compositions. The samples were obtained as ribbons by melt-spinning, their glass stability and crystallization were analyzed by differential scanning calorimetry and dilatometry, structural changes were followed by in situ synchrotron X-ray diffraction during annealing throughout glass transition and crystallization. The synchrotron results are compared with the calorimetric and dilatometric measurements and the structural changes occurred during annealing are determined and described for each alloy.     

X-ray diffraction analysis of modulated crystals: Review

The state of the art of X-ray diffraction analysis of modulated crystals is reviewed. The review begins with a brief historical overview followed by the consideration of the main concepts and notations used in this field. Then, methods of structural analysis of modulated crystals are considered with emphasis on recent achievements. The most interesting objects are listed, and the directions of investigation are outlined. Examples of analysis of both individual structures and families of modulated and incommensurate composite structures are given in terms of superspace symmetry.     

Optical and luminescent VUV spectroscopy using synchrotron radiation

The main processes of energy relaxation occurring in solids upon high-energy excitation are described, and the information that can be obtained by vacuum ultraviolet (VUV) spectroscopy for each relaxation stage is presented. The theoretical and experimental results obtained by the authors using synchrotron radiation are reported.     

Diamond monochromator-splitter with enhanced reflectivity for synchrotron radiation

It has been shown that a damaged surface layer can enhance the reflectivity of a diamond monochromator-splitter for synchrotron radiation. The X-ray diffraction analysis with the use of asymmetric Bragg reflections allowed the determination of the layer thickness and its mosaicity dispersion equal to 3 μm and 19″, respectively. In this case, the observed integrated intensity of a quasisymmetric 422 Laue reflection ( $Mo_{K_\alpha } $ radiation) exceeds its calculated value by a factor of 2.5 at a sufficiently high energy resolution (δE/E = 1.1 × 10^?5). The perspectives of the practical use of a diamond monochromator-splitter with enhanced reflectivity are also discussed.     

X-ray diffraction studies of fluid rubidium: From the liquid to a dense vapor

X-ray diffraction measurements have been carried out for fluid rubidium from the triple point up to supercritical conditions using synchrotron radiation at SPring-8. In order to achieve high- temperature diffraction experiments, we have developed a new sample cell made of molybdenum that is resistant to the highly corrosive nature of hot alkali metals. The use of the cell has made it possible to achieve stable and precise measurements at the supercritical region of fluid rubidium. It was observed that the position at the first peak of the pair distribution function starts to decrease around 1.0 g/cm³ with decreasing density, suggesting the possibility of dimerization in the density range where the fluid is still metallic.     

X-ray diffraction in thick perfect crystals with deformed subsurface layers

The diffraction of X-rays in thick perfect crystals with deformed subsurface layers has been investigated. It was shown that the kinematic scattering of X-rays took place in deformed layers, while the dynamical one occurred in the perfect part of the crystal, -its bulk; also, that in beams of X-rays diffracted on surface defects, the role played by the second harmonics of the applied characteristic radiation MoKα₁ was essential.     

Light diffraction by acoustically induced domains in nematic liquid crystals

The phenomenon of light diffraction by a system of linear domains formed in planar layers of nematic liquid crystals in an oscillating Couette flow, acoustically induced at sound frequencies, is investigated.     

Neutron and synchrotron radiation scattering by nonpolar magnetic fluids

The complex approach (which comprises different physical methods, including neutron and synchrotron radiation scattering) is justified in the structural analysis of magnetic fluids (MFs). Investigations of MFs based on nonpolar organic solvents with magnetite nanoparticles (2–20 nm in size) coated by various monocarboxylic acids have been performed. It is shown that the use of saturated linear acids with various alkyl chain (C12–C18) lengths instead of unsaturated oleic acid (alkyl chain C18 with a kink in the middle due to the double bond in the cis-configuration) in the classical stabilization procedure for the given type of magnetic fluids leads to a decrease in the mean size and polydispersity of nanoparticles in the final systems.     

Low temperature X-ray diffraction study of CdI2 crystals

Solid state structural transformations in polytypic crystals of cadmium iodide have been investigated at low temperatures using X-ray diffraction techniques. The crystals were cooled to liquid nitrogen and liquid helium temperatures employing three different methods. The results obtained are discussed on the basis of bond dissociation energies of interlayer and intralayer bonds and the possible mode of layer displacements in MX₂-type polytypic crystals.     

Complementarity of real-time neutron and synchrotron radiation structural investigations in molecular biology

General problems of the complementarity of different physical methods and specific features of the interaction between neutron and matter and neutron diffraction with respect to the time of flight are discussed. The results of studying the kinetics of structural changes in lipid membranes under hydration and self-assembly of the lipid bilayer in the presence of a detergent are reported. The possibilities of the complementarity of neutron diffraction and X-ray synchrotron radiation and developing a free-electron laser are noted.     

Study of doped higher manganese silicides crystals by transmission electron diffraction and electron backscatter diffraction

The microstructure of Al-, Ge-, and Mo-doped higher manganese silicide crystals (HMS), grown by the Bridgman method have been investigated by transmission electron diffraction, electron backscatter diffraction, scanning electron microscopy, and X-ray energy-dispersive spectrometry. It is shown that the matrix crystal has the Mn₄Si₇ structure. The introduction of Ge and Mo impurities into an HMS crystal results in the precipitation of Si-Ge solid solution and molybdenum disilicide. The size of precipitates varies in a wide range: from several nanometers to several hundreds of micrometers. The following orientation relationships between Ge-Si precipitates and the Mn₄Si₇ crystal were determined: (112) $[\bar 110]$ Ge-Si ‖ (010)[100] Mn₄Si₇. Polycrystalline MoSi₂ precipitates form a multicomponent texture along the [001] Mn₄Si₇ direction. Small amounts of cubic MnSi and Al-Mn-Si alloy precipitates were revealed. In addition, Al oxide was observed mainly in crystal pores. It is shown that 0.5–0.8 at % Al, 0.4–0.6 at % Mo, and 1.5–2.0 at % Ge impurities are incorporated into the Mn₄Si₇ lattice.