Vol 68, No 4 (2023)

The spatial distribution of linear defects in cuboctahedral single crystals of synthetic diamonds, grown under laboratory conditions by the high-pressure high-temperature (HPHT) method near the diamond–graphite equilibrium line, has been studied. Synthetic diamonds of this type have been studied for the first time by the X-ray topo-tomography using a laboratory X-ray source.

An analytical expression is obtained for the rocking curve of a double-crystal spectrometer, which does not require restrictions on the absorption cross section dependency on the wavelength. A modeled rocking curve (instrumental line) for the Bragg–Bragg spectrometric scheme is calculated using the example of an InSb crystal in the region of weak dependency between the absorption cross section and the wavelength and in the region of wavelengths close to the absorption resonance.

Cation-deficient Na_2–3xGd_xMoO₄ solid solutions in the NaGd(MoO₄)₂–Gd₂(MoO₄)₃ system have been simulated by the interatomic potentials method. The parameters and volume of unit cell, as well as density, bulk modulus, enthalpy, vibrational entropy, and heat capacity in dependence of the composition are determined. Temperature dependences of the heat capacity and vibrational entropy are plotted. The local structure of the solid solutions has been studied. It is shown that the vacancy–oxygen distances are on average 5.0% larger than the Na–O distances and 11.8% larger than the Gd–O distances. The sizes of these coordination polyhedra slightly increase with an increase in the gadolinium content, which is accompanied by an increase in the unit-cell size. The parameter c increases with a higher rate as compared to a, which is indicative of distortion of the unit cell and polyhedra.

Structural classes of the crystal structures consisting of mutually parallel chains of structural units (polymers) and constructed due to the sole bearing contact between polymer chains have been derived. In total, 43 structure classes have been found. Nets of bearing contacts in these classes belong to topological types sql, hxl, hcb, kgm, kgd, 2,4L2 and some other types of nets with doubly coordinated vertices. Examples of crystal structures of inorganic and organic polymers are presented.

A crystallographic analysis of two structures, monoclinic Nа8[{Re4(PO)4}(CN)12]⋅18H2O⋅CH3OH (I) and orthorhombic [(C6H5)4P]4 [Ta6I12(CN6)] (II), in which clusters of heavy atoms are significantly rarefied in space, so that their mutual arrangement cannot be explained only in terms of chemical interaction, has been performed. In structure I the crystallographic planes with a high atomic density (“skeletal” planes) are located in the regions with d_hkl = 10–5.5 Å and d_hkl < 3 Å. The planes in which atomic groups [Re4(PO)4] (playing the role of unified bulk objects) are concentrated are in fact selected in the first region. In the second region, ordering is implemented at the level of individual atoms. A crystallographic analysis showed that the structure basis is determined by the sites of heavy Re cations. A striking fact is that there are 1152 subcells and only 32 Re atoms per unit cell in this structure; i.e., only the fraction of 1/144 provides the basis of structure stability. In structure II “skeletal” planes are also absent in the range of d_hkl from ∼7 to ∼4 Å. The planes in the range of large dhkl characterize cluster ordering, whereas the planes in the range of small d_hkl characterize ordering of separate atoms. The geometry and local symmetry of the cluster group (Та6 octahedron) dictates the basis of translational symmetry—unified sublattice of sites, most of which are free of these atoms. The considered structures demonstrate the key role of heavy atoms in the formation of translational symmetry—the fundamental difference of the crystalline state from other condensed states. The newly formed structure retains partially local symmetry of cores (templates) of atomic groups, bound by strong chemical interactions, including the interactions between heavy and light atoms. The process of formation of a crystal structure from randomly oriented and randomly located templates—coherence assembly—is implemented according to the laws of dynamics of elastic media, where masses of atoms rather than their chemical characteristics are important.

A variety of the mineral nezilovite, containing antimony and an elevated amount of titanium, has been studied using microprobe and X-ray diffraction analysis. The diffraction experiment was performed on a crystal presenting an aggregate of nezilovite and högbomite with close unit-cell parameters. The parameters of the hexagonal cell of the nezilovite studied are a = 5.8855(2) Å, c = 23.092(1) Å, V = 692.73 (4) Å3,sp. gr. P6₃/mmc. The structural model is refined using a limited number of unique reflections 231F > 4σ(F) to R = 0.08. The crystallochemical formula is (Z = 2) PbZn2(Ti0.9Al0.1)(Al0.6Sb )Mn Fe O18.5(O,OH)0.5. The distribution of cations of this composition over structure sites is established. A basis of the mineral structure is a set of spinel layers, consisting of edge-sharing Fe³⁺ octahedra. They alternate with two heteropolyhedral layers: Zn tetrahedra combine (Al,Sb) octahedra in one layer, and five-vertex Ti polyhedra combine dimers of Mn³⁺ octahedra in the other layer.

Two new disulfatouranylates, Rb2[UO2(SO4)2(H2O)]⋅1.75H2O (I) and (N2H5)2[UO2(SO4)2(H2O)] (II), were synthesized and their structures were determined by single-crystal X-ray diffraction. In structures I and II, each uranyl ion is coordinated in the equatorial plane by four bidentate-bridging sulfate groups and one water molecule to form pentagonal-bipyramidal complexes with the crystal-chemical formula АВ₂² М1 (A =UO₂²⁺, B² =SO₄^2- , M1 = H2O). It was found that, while having the same composition [UO2(SO4)2(H2O)]^2–, the uranium-containing structural units are geometric isomers, which have a chain and layered structure in I and II, respectively.

Yttrium‒aluminum garnet single crystals, including cerium-doped ones, have been grown from melt by Bagdasarov’s method. A comparative spectroscopy study of garnet single crystals and specially prepared ceramics of the same composition has been carried out. The comparative analysis suggests that an increase in the concentration of cerium ions in the garnet crystals improves the spectral-luminescence and scintillation characteristics of the latter and facilitates effective quenching of the substrate luminescence. Ways of optimizing the synthesis conditions to improve the efficiency of scintillators based on {Y_1-xCe_x}₃Al₅O₁₂ garnet crystal have been proposed.

A magnetohydrodynamic domain model describing the motion of a nematic liquid with positive anisotropy of diamagnetic susceptibility in the splay distortion geometry is considered. The inertial term is taken into account in the equation of motion of a nematic model. This approach makes it possible to introduce dimensionless parameters into the model: ratios of Eriksen numbers to Reynolds numbers. The introduction of such parameters allows one to experimentally assess the relative role of elastic and viscous forces in nematics of different nature.

The study presents a comparative analysis of the structures of dried films of bacterial cellulose (BC) produced by bacteria of the Gluconacetobacter hansenii GH-1/2008 strain under static conditions of cultivation on nutrient media with different carbon sources, such as glucose, sucrose, maltose, fructose, and lactose. It was found that the supramolecular structure of the films is a three-dimensional network composed of orientationally ordered microfibrils with an average diameter from 30 to 60 nm, which consist of crystalline and amorphous regions. An analysis of the powder X-ray diffraction patterns demonstrated that the crystalline regions of microfibrils are formed by cellulose I. Depending on the composition of the nutrient medium, the degree of crystallinity of the films varies in the range from ~20 to 90%. It was found that, regardless of the carbon source, the top and bottom surfaces of BC films have different microstructures defined by static conditions of cultivation. Thus, the top surface of gel films contains pores with a diameter of up to 500 nm, whereas a wider pore size distribution (up to 600 nm) is observed on the bottom surface. The difference between the average pore sizes on the top and bottom surfaces varies from 95 to 180 nm and from 100 to 200 nm, respectively. The measurements of the mechanical properties of the films showed that the films produced by the cultivation on media containing fructose and sucrose have the maximum strength, whereas the films produced using lactose and maltose have the minimum strength. The data on the BC productivity of the GH-1/2008 strain were obtained.

Hot pressing of a Si single crystal in the bulk of electrolytic Cr powder at 1213 K, with subsequent annealing in air, leads to the formation of an intermediate polycrystalline silicide layer at the interface between the initial components. The phase composition and microstructure of the transition layer and its vicinity were investigated by scanning electron microscopy, X-ray energy-dispersive microanalysis, and electron backscatter diffraction. The transition layer has a crystal structure of the hexagonal phase of chromium disilicide (sp. gr. P6222). An additional annealing up to 120 h leads to insignificant recrystallization of small grains into larger ones.

The resolution of the high-intensity diffractometer, developed for the PIK reactor (Gatchina), is calculated both numerically and analytically. These two approaches give different results. All neutron trajectories calculated numerically are limited by the geometry of optical elements. Therefore, the diffraction profile has a trapezoidal shape, which can be seen well at large diffraction angles. Analytical formulas yield a Gaussian line profile. The difference in profiles leads to a difference in the resolution curves calculated numerically and analytically. This difference is especially pronounced for the diffractometers with medium and low resolution, optimized to the maximum intensity.

Статья посвящена крупному ученому и организатору науки, профессору Льву Михайловичу Блинову, посвятившему свою жизнь исследованию жидких кристаллов и организованных молекулярных структур. Лев Михайлович является основателем школы экспериментальных исследований органических пленок и жидких кристаллов в Советском Союзе, им воспитаны десятки молодых ученых, ставших кандидатами и докторами наук. Л.М. Блиновым написаны сотни научных статей, множество обзоров, монографий и учебников, читались лекции как в России, так и по всему миру. Кратко изложена биография Льва Михайловича, дан обзор его наиболее значимых достижений и отдельных публикаций, получивших широкий резонанс в научном сообществе. Приведены воспоминания учеников и коллег.