Crystallography Reports最新文献

An X-ray diffraction technique utilizing a synchrotron radiation source has been proposed and implemented to study the processes of magnetic domain structure evolution in external fields. Highly perfect single crystals of iron borate FeBO₃ were used as model objects. A series of  X-ray and magneto-optical experiments was performed to investigate the evolution of the magnetic domain structure in weak external magnetic fields. It has been established that the movement of domain walls leads to a stepwise broadening of the diffraction reflection curves of FeBO₃ crystals. It is demonstrated that X-ray diffraction studies of the magnetic domain structure can be useful for characterizing magnetic materials where direct observation of domains by magneto-optical and electron-microscopic methods is hindered.

The results of electron microscopy and energy-dispersive X-ray microanalysis studies of the structure and composition of the surface and near-surface layers of the Mg–Y–Zn–Nd–Yb–Zr alloy system with a long-period phase after irradiation by nanosecond laser pulses are reported. It is shown that in two-phase alloy, a nanocrystalline MgO layer with a thickness from 5 nm to several hundreds of nanometers is formed on the surface in the α-Mg matrix region. A recrystallized layer of columnar crystallites with a thickness of ~1 μm and a lateral size of 0.2–1 μm, with inclusions of cubic MgO, is formed under this layer. In the area of the intermetallic compound (Mg₁₂YZn–REE phase of the 18R type), a three-layer amorphous–crystalline trilayer is formed; it consists of a (15–20)-nm-thick amorphous surface layer, a (0.1–0.3)-μm-thick crystalline layer of columnar crystallites with lateral sizes of 0.1–0.5 μm under it, and a ~1-μm-thick amorphous intermetallic layer.

The results of studying the recombination-enhanced dislocation motion in GaN and 4H-SiC have been analyzed. It is shown that in both crystals, when irradiated by a low-energy electron beam, dislocations can shift at liquid nitrogen temperature. The activation energies of the dislocation glide stimulated by electron beam irradiation are estimated. Results demonstrating practically activation-free migration of double kinks along a 30° partial Si-core dislocation in 4H-SiC are presented. It is shown that localized obstacles significantly affect the dislocation motion in GaN both under the action of shear stresses and under irradiation. The excess charge carriers introduced into GaN by irradiation not only help to overcome the Peierls barrier but also stimulate dislocation unpinning from obstacles.

The paper presents the results of the many-year development of a new method for the temperature control of the crystal nucleation and growth. This method has made the basis of a setup, which allows the separate control of protein crystal growth processes in an automatic mode.

Digital processing of the 2D noisy X-ray diffraction images (2D-XDI) of a single point defect in a Si(111) crystal, recorded at the level of dispersion of statistical Gaussian noise of the detector using filtering methods, such as singular value decomposition and 1D-line-by-line smoothing of test 2D-XDI, is carried out. The efficiency of digital filtering of 2D-XDI is evaluated and analyzed by means of the control parameter FOM (figure-of-merit) value of reconstruction of the displacement field function of a point defect of Coulomb type f_h(r – r₀), (h is the diffraction vector, r₀ is the radius-vector of the defect position in the sample). It is shown that the filtering technique using the singular value decomposition of 2D-XDI works much better than the 1D line-by-line smoothing method of 2D-XDI, which, apparently, as applied to our problem, requires further research for its improvement.

The metal-organic polymer MIL-53(Fe) with the framework composition Fe(OH)(BDC)⋅(H₂O)₂ and the composite MIL-53(Fe)/GO (GO is graphene oxide) have been obtained by the solvothermal method and characterized by X-ray diffraction, X-ray absorption spectroscopy, IR Fourier spectroscopy, and scanning and transmission electron microscopy. It has been established that the MIL-53(Fe) in the MIL-53(Fe)/GO composition differs from the initial MIL-53(Fe) polymer by the absence of secondary phase (phases), a lower content of water molecules, a higher content of the solvent and Fe²⁺ ions, and the morphology and microstructure. In the photo-Fenton reaction, the degree of decomposition of RR195 dye in the presence of the MIL-53(Fe)/GO composite exceeds the degree of decomposition of the initial MIL-53(Fe) polymer, which remains almost invariable after three photo-reaction cycles.

The new bis(2,6-diaminopyridinium) tetrachlorozincate complex of the composition (С₅Н₈N(_{3}^{ + }))₂[ZnCl₄]^2– was synthesized by the reaction of 2,6-diaminopyridine with a Zn(II) ion in an ethanolic solution of hydrochloric acid. The composition and the molecular and crystal structure of the synthesized complex were determined by X-ray diffraction analysis. The composition of the metal complex was confirmed by elemental analysis. The chemical bonds were investigated by IR spectroscopy. Intermolecular interactions in the crystal were studied by the Hirshfeld surface analysis. The stability of the complex was determined by thermal analysis and it is, apparently, attributed to intramolecular hydrogen bonds.

The anthropogenic calcium fluorosilicate “kutyukhinite” Ca₅[SiO₄]₂F₂ from burnt dumps of the Chelyabinsk coal basin has been studied by single crystal and powder X-ray diffraction analyses in a wide temperature range. “Kutyukhinite” (P2₁/a, a = 11.4985(4) Å, b = 5.0535(2) Å, c = 8.7848(3) Å, β = 109.008(4)°, V = 482.63(3) ų, R₁ = 0.0183) is an anthropogenic analogue of kumtyubeite, which belongs to the structural type of chondrodite. The empirical formula of “kutyukhinite” is Ca_5.02[Si_1.99O_7.98]F_2.04. Upon heating, its crystal structure expands anisotropically, with the direction of maximum thermal expansion close to the [100] direction. The relative change in bond lengths in silicon–oxygen tetrahedra with increasing temperature (27–927 °C) is less than 0.6%, which is within the margin of error. At the same time, the relative increase in the average bond length 〈Ca–O〉 varies from 1% (〈Ca1–O〉) to 1.5% (〈Ca3–O〉). The largest relative change of  2% was found for the average bond length 〈Ca3–F1〉.

Crystals of hydrogen-containing compounds Cs₄(HSO₄)₃(H₂PO₄) and NH₄Cl⋅2H₂SeO₃ have been studied using the neutron diffraction methods implemented at the comissioned experimental single-crystal neutron diffraction station (MOND) installed on the thermal neutron beam of the IR-8 reactor of the National Research Centre “Kurchatov Institute.” The obtained results demonstrate the capabilities of the techniques for localizing hydrogen atoms with high accuracy and characterizing hydrogen-bonded systems, the information about which is necessary for establishing correlations between the atomic, real structure and the physico-chemical properties of the investigated crystals.

The phase formation in the system of triple phosphates Sr–M²⁺–Ln³⁺ (M²⁺ = Zn²⁺, Mg²⁺, Mn²⁺; Ln³⁺ = Eu³⁺, Tb³⁺) is considered. Specific features of the strontiowhitlockite phase formation and the isomorphism in the series of phosphates Sr(_{{9-x}})Mn_xTb(PO₄)₇, Sr(_{{9-x}})Mg_xEu(PO₄)₇, and Sr(_{{9-x}})Zn_xEu(PO₄)₇ (0 ≤ x ≤ 1.0), obtained by solid-phase synthesis, have been studied. It is shown that a continuous series of solid solutions of these compositions cannot be formed. Crystallization of phases with strontiowhitlockite-type structures is observed for only stoichiometric phosphates Sr₈MgEu(PO₄)₇ and Sr₈ZnEu(PO₄)₇. Crystal chemical analysis of the possibility of strontiowhitlockite phase formation in the studied series is performed. It is shown that samples with the strontiowhitlockite structure crystallize in the centrosymmetric space group (sp. gr. R(bar {3})m), in contrast to the mother structure of mineral whitlockite and its calcium-based synthetic analogues. The conditions for the formation of phosphates with the stronciowhitlockite structure are indicated. The photoluminescence properties have been investigated. It is shown that the samples exhibit stable photoluminescence in the red-orange region due to the emission of Eu³⁺ cations, whereas a quenching effect is observed in the Sr(_{{9-x}})Mn_xTb(PO₄)₇ series.