Crystal structure of K2.47Nb2.85Ti1.15P2.5O17

The structure of a crystal grown by crystallization from flux in the K₂O-TiO₂-Nb₂O₅-P₂O₅ system was studied by the methods X-ray diffraction analysis at room temperature. The crystals of the composition K_2.47Nb_2.85Ti_1.15P_2.5O₁₇ are monoclinic, a = 13.7864(7) Å, b = 6.4078(3) Å, c = 16.9384(7) Å, β = 83.15(1)°, sp. gr. P2/n. The structure was solved by the direct method using the SHELXS86 program package and refined by the JANA96 program. The crystal structure consists of a three-dimensional framework of sharing-vertices (Nb,Ti)O₆-octahedra and the PO₄-tetrahedra and two types of channels along the diagonal [101] direction, which are statistically occupied by potassium cations providing ionic transport in the compound.     

X-ray diffraction study of cerium-and thulium-doped (Sr,Ba)Nb2 O6 single crystals

The structural models of cerium-and thulium-doped (Sr_0.61Ba_0.39)Nb₂O₆ solid solutions were established and refined on the basis of single-crystal X-ray diffraction data. The dopants were located, and their concentrations in the specimens were refined. The effect of the Sr/Ba ratio and doping with rare earth elements on the structural characteristics of (Sr_xBa_1-x )Nb₂O₆ crystals was analyzed.     

X-ray investigations of BaLaGa3O7 single crystals

X-ray investigations have been carried out on single crystals of BaLaGa₃O₇. Debye temperature as well as thermal expansion coefficients were determined, and values of which are respectively     

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.     

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.     

X-ray diffraction study of crystals under a static electric field

This paper gives an overview of the effect of electric field on the diffracted intensity and contrast on the X-ray topographs recorded from crystals of non-linear and electro-optic materials, ionic conductors, semiconductors, insulators and ferro-electric materials. Application of a dc electric field gives rise to a change in the diffracted intensity by several orders of magnitude and contrast on the topographs. The effect is illustrated with examples of -LiIO₃, KTiOPO₄, LiN₂H₅SO₄, KNbO₃, LiNH₄SO₄, quartz, silicon etc. and the mechanism for it is discussed.     

Application of X-ray diffraction topography for the study of Al single crystals plastically deformed at low temperatures

The Lang method has been used to investigate regularities and peculiarities of formation of Al single crystal dislocation structure in various stages of the stress-strain curve at 77.3 and 4.2°K up to high strains. The low temperature deformation of crystals has been found to cause a sharp localization of the deformation into slip bands that correspond to different glide systems. A comparison with metallography is added.     

X-ray diffraction study of Ca0.88Gd0.12F2.12 single crystals with a modified fluorite structure

The characteristic structural features of a single crystal of the anion-excessive fluorite phase Ca_0.88Gd_0.12F_2.12 have been studied by X-ray diffraction analysis (MoK _α radiation), sp. gr. Fm3m, Z = 4, a = 5.5000(4) Å. The structure was refined in the anharmonic approximation of thermal atomic vibrations to R _w = 0.0047. A total of 78 independent structure amplitudes were measured; 14 parameters were refined; sinθ/λ ≤1.13 Å^?1. In the structure under study, the replacement of the divalent Ca²⁺ cations by the trivalent Gd³⁺ cations in the position 4a (0, 0, 0) resulted in the statistical distribution of the fluorine atoms over three positions of the sp. gr. Fm3m. Thus, the fluorine atoms occupy the position 8c (1/4, 1/4, 1/4), the main position in the fluorite structure type, and the position 32f (v, v, v) with v = 0.417(1) on threefold symmetry axes. In addition, some fluorine atoms are shifted from the main 8c position along the threefold symmetry axis to the position 32f (w, w, w) with w = 0.313(2).     

Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.     

X-ray diffraction topography and diffuse scattering techniques applied to study the defect structure of plastically deformed al single crystals

X-ray diffraction topography and diffuse scattering techniques were used to study the defect structure formation of plastically deformed Al single crystals. The investigated X-ray scattering has been found out materially to depend upon the character of the dislocation structure (upon the geometry of the dislocation distribution). This dependence is manifested in different distribution of the intensity and in the changed form of the isointensity curves of diffuse and regular (Laue) reflections. In spite of the fact that the distribution of the internal stresses acting in different glide systems under conditions of uniaxial stretching is of complicated character, it is possible to trace the development of the glide process in the body of a sample and to obtain satisfactory interference patterns both of regular reflexions (on topograms) and of diffuse ones (on Laue photographs) up to severe deformations of a crystal at 300, 4.2, and 1.6 K. The following diffuse effects connected with structural changes in deformed crystals have been ascertained on the X-ray photographs:

• —diffuse regions are elongated in the reciprocal lattice space along the glide directions or other crystallographic directions;
• —these diffuse regions are split into separate areas along the directions of the said elongations;
• —the diffuse regions are changed in length: the diffuse reflexes are diffused or condensed;
• —the diffuse scattering isointensity curves are “zigzag”-shaped.

     

Preliminary X-ray diffraction study of crystals of photosystem II from Thermosynechococcus elongates

Photosystem II (PSII) is a multicomponent enzyme complex that catalyzes the light-induced water splitting to molecular oxygen, protons, and electrons. Photosystem II is located in the membranes of cyanobacteria, green algae, and plants. The crystallization of this complex from the thylakoid membranes poses great difficulties. The high sensitivity of photosystem II to light and radiation has an adverse effect on the crystal quality, as well as on the quality of X-ray diffraction data. This is the reason why the crystal structure of PSII from Thermosynechococcus elongates has as yet not been determined at high resolution. The optimization of the strategy for collecting X-ray diffraction data from PSII crystals has resulted in an increase in the resolution to 2.75 Å, which made it possible to determine the positions of ions and some water molecules playing an important role in the functioning of PSII.     

Structural study of thiosaccharin by single crystal X-ray diffraction and infrared spectroscopy

The structure of thiosaccharin (1,2-benzisothiazol-3(2H)-thione 1,1-dioxide) has been investigated by X-ray diffraction and infrared spectroscopic methods. The compound crystallizes in the orthorhombic space groupFdd2 witha=26.591(3),b=25.058(3),c=4.934(5) Å,Z=16. The structure consists of thiosaccharin molecules bonded to each other through N–H...O intermolecular hydrogen bonds. The infrared spectra of the thiosaccharin at room and liquid-nitrogen temperature were recorded. The spectral features in the N–H stretching region were correlated with the crystallographic data on the geometry of the N–H...O hydrogen bonding. In an attempt to assign the bands due to the SO₂ stretching modes, the spectrum of thiosaccharin was compared with that of saccharin (1,2-benzoisothiazole-3(2H)-one, 1,1-dioxide).     

X-ray diffraction study of crystals of the organic luminophore Orlyum White 520T

The crystal and molecular structures of two crystal forms (pale yellow form 1 and yellow form 2) of N-[2-(4-oxo-4H-benzo[d][1,3]oxazin-2-yl)phenyl]naphthalene-2-sulfonamide (Orlyum White 520T), which is an organic luminophore with an anomalously high Stokes shift, were determined. Crystal 2 is a solvate with para-xylene. Crystal 1 is a solvent-free form. The molecular geometry in crystal 1 differs from that in 2 only in the orientation of the SO₂ Ar substituent. The bond-length distribution in the planar moiety of the molecule in crystal 1 is virtually identical to that in 2, but the bonds in the NH-SO₂ Ar-bearing benzene ring in crystal 1 are systematically longer than the corresponding bonds in crystal 2. This fact can be attributed to the crystal-packing effects. In 2 the molecules form stacked dimers with π-stacking interactions between two planar conjugated tricyclic systems. The charge transfer in this system accounts for the intensification of the color of these crystals and the observed difference in the optical properties of 1 and 2.     

Synthesis and Photocatalytic Properties of TiO2 Intercalated H4Nb6O17

Abstract

TiO₂ intercalated H₄Nb₆O₁₇ has been synthesized by the reactions of H₄Nb₆O₁₇ with a titanyl acylate complex followed by UV irradiation. The gallery height, specific surface area and Ti content of the sample synthesized by using titanyl acylate complex were larger than that using TiO₂ sol solution. Furthermore, the photocatalytic activity of the TiO₂ pillared H₄Nb₆O₁₇ prepared using a titanyl acylate precursor was twice larger than that fabricated using a TiO₂ sol solution.     

Formation conditions and temperature dependence of forbidden reflections during resonant X-ray diffraction in zinc oxide single crystals

Different mechanisms of formation of purely resonant reflections hhl (h = 2n + 1) during resonant diffraction of X-ray synchrotron radiation in zinc oxide, whose intensity very strongly changes with an increase in temperature, are considered. Such reflections, forbidden in the dipole-dipole scattering, can be excited owing to the dipole-quadrupole scattering and the anisotropy of X-ray susceptibility induced by thermal motion of atoms and point defects. Different contributions are theoretically considered and it is shown that they can be separated owing to their different temperature dependences.     

X-ray,optical and electrical study of melt-grown CdI2 single crystals

CdI₂ has been purified using the zone-refining technique by giving 20 passes. Single crystals grown from the starting material showed arcing in the X-ray oscillation photographs whereas it is absent in the crystals grown from the zone refined material. These crystals are found to be of the 4 H type. DC conductivity studies were made on these crystals at various stages of purification. The surface morphology of these crystals have been studied using an optical microscope.     

Czochralski growth and characterization of Dy: La3Ga5.5Nb0.5O14 single crystals

Dysprosium (Dy) doped La₃Ga_5.5Nb_0.5O₁₄ single crystals were grown by the traditional Czochralski method along z‐axis. The structure of the crystal has been studied by X‐ray powder diffraction method, and the unit‐cell parameters are calculated to be a=8.22070 Å, c=5.12533 Å and V=299.965 ų. The segregation coefficient of Dy³⁺ in La₃Ga_5.5Nb_0.5O₁₄ crystal was measured by X‐ray fluorescence analysis. For 1 mol% doping level in the melt, the distribution coefficient of Dy³⁺ was determined to be 0.341 wt%. Specific heat, thermal expansion and transmission spectrum of Dy: La₃Ga_5.5Nb_0.5O₁₄ single crystals have been measured. The fluorescence spectra of Dy³⁺: La₃Ga_5.5Nb_0.5O₁₄ crystals were measured at room temperature, and there were four emission transitions occurring at 479, 576, 662 and 754 nm, respectively. The fluorescent lifetimes measurement results show 1.0% Dy: La₃Ga_5.5Nb_0.5O₁₄ possesses shorter fluorescence decay time (303.4 μs) than does 1.0%Dy:LGS (436.12 μs). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

钙钛矿型层状化合物K2Pr2Ti3O10的合成及XRD研究

在K2CO3-镧系元素氧化物(Pr2O3)-TiO2三元体系中,用固相反应法合成K2Pr2Ti3O10,利用X射线粉晶衍射仪对K2Pr2Ti3O10进行扫描测定,获得X射线衍射数据,进行指标化,得到其晶胞参数。XRD分析结果表明,K2Pr2Ti3O10为四方晶系,空间群I4/mmm。     

Synthesis and magnetic properties of copper metaborate single crystals, CuB2O4

Large high-quality single crystals of copper metaborate are grown on the basis of the phase diagram of the ternary Li₂O-CuO-B₂O₃ system. Bright blue crystals with a volume of about 1 cm³ were grown by the method of spontaneous crystallization while slowly cooling the melt. The magnetic susceptibility and electron spin resonance were measured. It is shown that the effective magnetic moment of a Cu²⁺ ion is equal to 1.6 μ_B and the g-factor, to 2.170 and 2.133 for the magnetic field oriented parallel and perpendicular to the fourfold axis, respectively. At 21 and 10 K, sharp anomalies of magnetic susceptibility are observed.     

Synthesis and X-ray diffraction study of new uranyl malonate and oxalate complexes with carbamide

Two new malonate-containing uranyl complexes with carbamide of the formulas [UO₂(C₃H₂O₄)(Urea)₂] (I) and [UO₂(C₃H₂O₄)(Urea)₃] (II), where Urea is carbamide, and one uranyl oxalate complex of the formula [UO₂(C₂O₄)(Urea)₃] (III) were synthesized, and their crystals were studied by X-ray diffraction. The main structural units in crystals I are the electroneutral chains [UO₂(C₃H₂O₄)(Urea)₂]_∞ belonging to the crystal-chemical group AT¹¹M₂¹ (A = UO₂²⁺, T¹¹ = C₃H₂O₄^2-, M¹ = Urea) of uranyl complexes. Crystals II and III are composed of the molecular complexes [UO₂(L)(Urea)₃], where L = C₃H₂O₄^2- or C₂O₄^2-, belonging to the crystal-chemical group AB⁰¹M₃¹ (A = UO₂²⁺, B⁰¹ = C₃H₂O₄^2- or C₂O₄^2-, M¹ = Urea). The characteristic features of the packing of the uranium-containing complexes are discussed in terms of molecular Voronoi–Dirichlet polyhedra. The effect of the Urea: U ratio on the structure of uranium-containing structural units is considered.