Physical Methods for Determining the Phase Composition of Gallstones

Crystallography Reports - Gallstones with a zonal morphological structure have been studied using X-ray microtomography, X-ray diffraction analysis, Raman spectroscopy, and elemental analysis....     

Influence of the X-Ray Spectrum on the Tomographic Reconstruction of Porous Ceramic Membranes

Crystallography Reports - X-ray microtomography is used for non-destructive reconstruction of the internal morphological structure of objects. The influence of the tomographic experiment conditions...     

Crystal structure of the mineral (Na,Ca,K)2(Ca,Na)4(Mg,Fe)5(Mg,Fe,Ti)5[Si12Al4O44](F,O)4: a triclinic representative of the amphibole family

A mineral belonging to the amphibole family found at the Rothenberg paleovolcano (Eifel, Germany) was studied by single-crystal X-ray diffraction. The triclinic pseudomonoclinic unit-cell parameters are a = 5.3113(1) ?, b = 18.0457(3) ?; c = 9.8684(2) ?, ?? = 90.016(2)°, ?? = 105.543(4)°, ?? = 89.985(2)°. The structure was solved by direct methods in sp. gr. P1 and refined to the R factor of 2.7% based on 6432 reflections with |F| > 3??(F) taking into account twinning. The mineral with the idealized formula (Na,Ca,K)₂(Ca,Na)₄(Mg,Fe)₅(Mg,Fe,Ti)₅[Si₁₂Al₄O₄₄](F,O)₄ has some symmetry and structural features that distinguish it from other minerals of this family.     

Crystal and molecular structure of n-hexyloxyphenyl n-octyloxybenzoate

The X-ray crystal structure of n-hexyloxyphenyl n-octyloxybenzoate C₈H₁₇O-C₆H₄-COO-C₆H₄-OC₆H₁₃, which is a liquid-crystal compound, was determined. This compound forms smectic and nematic phases upon melting. A crystal-packing analysis revealed the following two types of structure-forming elements in the centrosymmetric pairs of molecules: a ??-stacking interaction and a C-H...??-system interaction. In the pairs of molecules linked by the latter type of interactions, there are two such interactions per pair, whereas one interaction occurs per pair of molecules linked by a ??-stacking interaction. Hence, the former pair of molecules is more stabilized through weak directional interactions than the latter pair.     

Anomalous small-angle scattering as a way to solve the Babinet principle problem

X-ray absorption spectra (XAS) have been used to determine the absorption edges of atoms present in a sample under study. A series of small-angle X-ray scattering (SAXS) measurements using different monochromatic X-ray beams at different wavelengths near the absorption edges is performed to solve the Babinet principle problem. The sizes of clusters containing atoms determined by the method of XAS were defined in SAXS experiments. In contrast to differential X-ray porosimetry, anomalous SAXS makes it possible to determine sizes of clusters of different atomic compositions.     

An interpretation of three intersections of cubic and rhombohedral structures based on the conservative nature of force skeletons

A crystallographic analysis of the structures of inorganic compounds has shown the uniformity of ??force skeletons??: pseudotranslational sublattices of atoms determining the structure of different classes of materials. At three specific c _hex/a _hex ratios, structures with a rhombohedral cell can be considered in the pseudocubic representation with P, I, and F cells (c _hex/a _hex is, respectively, 1.225, 0.612, and 2.45). The large fraction of structures with c _hex/a _hex ratios close to these values indicates the stability of these atomic constructions. Force skeletons with a typical hexagonal subcell (different for cations and anions), which reflects the relationship of these structures with the high-symmetry structural types of sphalerite (ZnS) and galena (PbS), have been established for the representative group of sulfides structures with a cell parameter ??4 ? in the direction perpendicular to the mirror plane.     

Ionic conductivity of the phases of five types formed in the BaF2-GdF3 system

The ionic conductivity has been measured in ceramic phases of five structure types found in the BaF₂-GdF₃ system: the fluorite type (CaF₂), its trigonal and tetragonal distortions, the tysonite type (LaF₃), and the orthorhombic ??-YF₃ modification. The phases have been obtained by solid-phase synthesis from BaF₂ and GdF₃ mixtures in hermetic nickel containers at 925, 964, and 1067°C for 108?C360 h in a fluorine atmosphere. Their conductivity ?? is compared in correlation with the composition and structure type. The highest conductivity values are found for the tysonite Gd_{1 ? y} Ba _y F_{3 ? y} phase (0.10 ?? y ?? 0.25): (1?2) × 10^?3 S/cm at 683 K. The ordered Ba_0.60Gd_0.40F_2.40 and Ba_0.57Gd_0.43F_2.43 phases with fluorite-derived structures and different degrees of order are characterized by the lowest conductivities: i(1.5?3.5 × 10^?5) S/cm.     

Properties characterization of the Cu68.5Ni12P19.5 alloy at elevated temperatures

The Cu_68.5Ni₁₂P_19.5 alloy was cast into the ribbons using melt spinning (23 m/s). The amorphous ribbon in the as-cast state was investigated by differential thermal analysis (DTA), dynamic mechanical analysis (DMA), resistivity measurements and X-ray diffraction ‘in situ’ at different temperatures. The work presents attempts to find correlation between the changes of the mechanical properties presented by DMA cycles and during the other tests. The measurements of the relative resistivity R/R₀ versus temperature for repeated heating and cooling cycles to different temperatures show changes of the temperature coefficient of resistivity (TCR) indicating reversible and irreversible transformations in the studied alloy.     

X-ray investigations of surface roughnesses

The unique potentialities and prospects for practical use of the X-ray scattering method as applied to the study and testing of surface roughnesses are considered. The high sensitivity, informative capability, and reliability of this method are demonstrated by using numerous examples. The results obtained by the X-ray scattering method at different wavelengths are compared with the available data of atomic-force microscopy.     

X-ray microscopy of track membranes and biological objects in the soft-and hard-wavelength ranges

The methods used to obtain X-ray images of track membranes and various biological objects in the soft (20 nm) and hard (0.2–0.02 nm) wavelength ranges have been considered. In the range of soft X-rays, the images were obtained in a Schwarzshild microscope. In the spectral range of hard X-ray radiation, various methods were used including the use of Fresnel zone plates, asymmetric reflecting crystals, X-ray microradiography and microtomography.     

Hydrogen bonds in the crystal structures of vanadyl phosphates Rb(VO2)[HPO4] and CsAl(VO)[PO4]2(H2O)

The crystal structures of two vanadyl phosphates, Rb(VO₂)[HPO₄] (a = 7.029(4) ?, b = 9.513(6) ?, c = 18.049(10) ?, sp. gr. Pbca, Z = 8, ??_calcd = 2.910(3) g/cm³) and CsAl(VO)[PO₄]₂(H₂O) (a = 8.0128(13) ?, b = 8.0714(13) ?, c = 14.118(2) ?, ?? = 106.302(2)°, sp. gr. I2₁/c, Z = 4, ??_calcd = 3.295(1) g/cm³), obtained by hydrothermal synthesis, have been refined using X-ray diffraction (Bruker Smart diffractometer, T = 100 K). Hydrogen atoms are located, and their coordinates and thermal parameters are refined. The geometric characteristics of hydrogen bonds are calculated and their crystallochemical function is analyzed. The topological and genetic relationships of the vanadyl phosphates under study with the compounds of derivative structural types are revealed.     

Structure and properties of quartz crystals grown from fluoride solutions: I. The morphology of basal pinacoid habit

The mechanism of growth of quartz crystals from fluoride media has been investigated. It is shown by different independent methods (selective etching, X-ray diffraction analysis, optical microscopy) that the faceted forms of autonomous growth regions (trigonal pyramids formed on nonsingular crystal faces) are unstable and degenerate during growth. This degeneracy is accompanied by torsion deformation of autonomous growth regions and, as a result, formation of a series of hollow helical channels at boundaries of autonomous growth regions, whose axes make an angle of ～16° with the OZ axis, and their projections on the XOY plane are directed along the +X axes.     

Multilayer X-ray mirrors for the (4.4–5)-nm carbon-window spectral region

Cr/C-based multilayer X-ray mirrors intended for the reflection of X-ray radiation in the “carbon-window” spectral region (λ = 4.4–5 nm) are fabricated and studied. The structures are formed by magnetron sputtering at different deposition parameters. Under normal incidence, record reflection coefficients up to 15% are reached. The structural parameters of the mirrors are investigated by reflectometry at wavelengths of 0.154 and 4.47 nm.     

Compositional dependence of the optical properties of amorphous Sb2Se3−xSx thin films

Thin films of Sb₂Se_3−xS_x solid solutions (x = 0, 1, 2, and 3) were deposited by thermal evaporation of presynthesized materials on glass substrates held at room temperature. The films compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). X-ray diffraction studies revealed that all the as-deposited films as well as those annealed at T_a < 423 K have amorphous phase. The optical constants (n, k) and the thickness (t) of the films were determined from optical transmittance data, in the spectral range 500-2500 nm, using the Swanepoel method. The dispersion parameters were determined from the analysis of the refractive index. An analysis of the optical absorption spectra revealed an Urbach’s tail in the low absorption region, while in the high absorption region an indirect band gap characterizes the films with different compositions. It was found that the optical band gap energy increases quadratically as the S content increases.     

Influence of annealing on the physical properties of filtered vacuum arc deposited tin oxide thin films

Tin oxide (SnO₂) thin films were deposited on UV fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at room temperature (RT). As-deposited films were annealed at 400 and 600 °C in Ar for 30 min. The film structure, composition, and surface morphology were determined as function of the annealing temperature using X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the SnO₂ thin films deposited on substrates at RT indicated that the films were amorphous, however, after the annealing the film structure became polycrystalline. The grain size of the annealed films, obtained from the XRD analysis, increased with the annealing temperature, and it was in the range 8-34 nm. The AFM analysis of the surface revealed an increase in the film surface average grain size from 15 nm to 46 nm, and the surface roughness from 0.2 to 1.8 nm, as function of the annealing temperature. The average optical transmission of the films in the visible spectrum was >80%, and increased by the annealing ∼10%. The films’ optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the range 1.83-2.23 and 1.85-2.3, respectively. The extinction coefficients, k(λ), of as-deposited and annealed films were in the range same range ∼0-0.5. The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, increased with the annealing temperature from 3.90 to 4.35 eV. The lowest electrical resistivity of the as-deposited tin oxide films was 7.8 × 10⁻³ Ω cm, however, film annealing resulted in highly resistive films.     

Crystal structure of a new mineral lahnsteinite Zn4(SO4)(OH)6 · 3H2O

A sample of a new mineral from the oxidation zone of the hydrothermal Pb, Zn, Ag Friedrichssegen deposit (Rhineland-Palatinate, Germany) was studied by single-crystal X-ray diffraction. The parameters of the triclinic (pseudoorthorhombic) unit cell are found to be a = 8.312(1) ?, b = 14.545(1) ?, c = 18.504(2) ?, ?? = 89.71 (1)°, ?? = 90.05(1)°, ?? = 90.13(1)°, and V = 2237.3(3) ?³. The structure is solved by direct methods into the sp. gr. P1 and refined to an R factor of 10.7% using 3788 reflections with |F| > 3??(F) in the isotropic-anisotropic approximation. The crystallochemical formula of lahnsteinite (Z = 8) is [(Zn_2.6Fe_0.3Cu_0.1)^VI(OH)₃][Zn^IV(OH)₃(H₂O)][SO₄] · 2H₂O, where the compositions of the layer composed of Zn octahedra and isolated Zn and S tetrahedra are given in square brackets. The mineral under study is chemically and structurally similar to namuwite and is a natural analog of synthetic zinc hydroxide sulfate trihydrate.     

Effect of the inhomogeneous structure of freely suspended smectic-A films on the dynamics of fluctuations of smectic-layer displacements

The dynamics of fluctuations of smectic-layer displacements in freely suspended smectic-A films is studied theoretically with due regard for the dependence of the transverse-bending moduli K and extension (or compression) of smectic-B layers on the distance to the free surfaces of the films. The temperature dependences of the dynamic correlation functions are calculated for fluctuations of layer displacements in films of various thicknesses and then used to calculate the correlations between the X-ray intensities scattered by the film at different moments of time. The calculations were performed within a wide temperature range. It is shown that the influence of temperature on the X-ray dynamics of fluctuations of layer displacements in freely suspended smectic-A films can be detected in the experiments on the dynamical scattering by rather thick films (layer number N ≥ 100) at considerably high values of the recoil-momentum component in the film plane (≥10⁶ cm^?1).     

Crystallinity of the mixed phase silicon thin films by Raman spectroscopy

Raman spectra of the mixed phase silicon films were studied for a sample with transition from amorphous to fully microcrystalline structure using four excitation wavelengths (325, 514.5, 632.8 and 785 nm). Factor analysis showed the presence of two and only two spectrally independent components in the spectra within the range from 250 to 750 cm^?1 for all four excitation wavelengths. The 785 nm excitation was found optimal for crystallinity evaluation and by comparison with surface crystallinity obtained by atomic force microscopy, we have estimated the ratio of integrated Raman cross-sections of microcrystalline and amorphous silicon at this wavelength as y = 0.88 ± 0.05.     

Crystal structure of magnesioneptunite

The crystal structure of the new mineral magnesioneptunite (K_0.8Na_0.1?0.1)Na₂Li(Ti_0.39Mg_0.34Fe_0.27)₂(Ti_0.59Mg_0.22Fe_0.19)₂[Si₄O₁₁]₂(O,OH) from the xenolith of Verkhnechegemskaya caldera (Lakarga Mountain, North Caucasus) has been investigated by X-ray diffraction (XCalibur-S diffractometer, R = 0.0244): a = 16.3271(7) ?, b = 12.4788(4) ?, c = 9.9666(4) ? ?? = 115.651(5), V = 1830.5(1) ?³, sp. gr. C2/c, Z = 4, and ??_calcd = 3.152 g/cm³. The disordered distribution of Ti, Mg, and Fe atoms in the octahedra forming the basis of the cationic framework is established. It is shown that the isomorphic occupation of octahedral positions by cations of three types corresponds to the centrosymmetric crystal structure and is likely caused by the high-temperature crystallization of the mineral.     

Radiation-induced defects in fluorine-doped silica-based optical fibers: Influence of a pre-loading with H2

We investigated the effects of 10-keV X-ray radiation on the transmission properties of F-doped optical fibers in the 200–850 nm range of wavelengths (1.5–6 eV). We also studied the influence of pre-loading this kind of fibers with hydrogen on its radiation sensitivity. Our results showed that, for our experimental conditions (pre-treatment with H₂ several months before irradiation with diffusion of all the H₂ out the fiber core and cladding before X-ray exposure), this pre-treatment increases the radiation-induced attenuation in the ultraviolet part (200–300 nm) of the spectrum. A previous H₂-loading has no influence at greater wavelengths. The nature of the radiation-induced point defects is discussed from the decomposition analysis of the attenuation spectra with Gaussian bands.