Том 61, № 4 (2016)
- Год: 2016
- Статей: 25
- URL: https://journals.rcsi.science/1063-7745/issue/view/11917
Reviews
Natural science methods in field archaeology, with the case study of Crimea
Аннотация
The natural science methods applied in archaeological field survey are briefly reviewed. They are classified into several groups: remote sensing (analysis of space and airspace photographs, viewshed analysis, study of detailed topographic and special maps, and three-dimensional photogrammetry), geophysical survey, and analysis of cultural layer elements (by geochemical, paleosol, and other methods). The most important principle is the integration of complementary nondestructive and fast natural science methods in order to obtain the most complete and reliable results. Emphasis is placed on the consideration of geophysical methods of the study, primarily, magnetic exploration. A multidisciplinary study of the monuments of ancient Chersonesos and its “barbarian” environment is described as an example of successful application of a complex technique.
Diffraction and Scattering of Ionizing Radiations
Peculiarities of section topograms for the multiple diffraction of X rays
Аннотация
The distortion of interference fringes on the section topograms of single crystal due to the multiple diffraction of X rays has been investigated. The cases of the 220 and 400 reflections in a silicon crystal in the form of a plate with a surface oriented normally to the [001] direction are considered both theoretically and experimentally. The same section topogram exhibits five cases of multiple diffraction at small azimuthal angles for the 400 reflection and MoKα radiation, while the topogram for the 220 reflection demonstrates two cases of multiple diffraction. All these cases correspond to different combinations of reciprocal lattice vectors. Exact theoretical calculations of section topograms for the aforementioned cases of multiple diffraction have been performed for the first time. The section topograms exhibit two different distortion regions. The distortions in the central region of the structure are fairly complex and depend strongly on the azimuthal angle. In the tails of the multiple diffraction region, there is a shift of two-beam interference fringes, which can be observed even with a laboratory X-ray source.
Structure of Inorganic Compounds
Structure and mechanical properties of foils made of nanocrystalline beryllium
Аннотация
The phase composition and structural features of (45–90)-μm-thick foils obtained from nanocrystalline beryllium during multistep thermomechanical treatment have been established using electron microscopy, electron diffraction, electron backscattering diffraction, and energy-dispersive analysis. This treatment is shown to lead to the formation of a structure with micrometer- and submicrometer-sized grains. The minimum average size of beryllium grains is 352 nm. The inclusions of beryllium oxide (ВеО) of different modifications with tetragonal (sp. gr. P42/mnm) and hexagonal (sp. gr. P63/mmc) lattices are partly ground during deformation to a size smaller than 100 nm and are located along beryllium grain boundaries in their volume, significantly hindering migration during treatment. The revealed structural features of foils with submicrometer-sized crystallites provide the thermal stability of their structural state. Beryllium with this structure is a promising material for X-ray instrument engineering and for the production of ultrathin (less than 10 μm) vacuum-dense foils with very high physicomechanical characteristics.
Structure of Gd0.95Bi0.05Fe3(BO3)4 single crystals at 293 and 90 K
Аннотация
The structure of GdFe3(BO3)4 single crystals has been studied by X-ray diffraction at 293 and 90 K. The crystals are grown from a flux in the Bi2Mo3O12–B2O3–Li2MoO4–Gd2O3–Fe2O3 system. The results of chemical analysis and structural study show that these crystals contain bismuth as an impurity. It is found that bismuth atoms are located at gadolinium sites in the structure. A decrease in the temperature is accompanied by a lowering of the symmetry from sp. gr. R32 (at 293 K) to sp. gr. P3121 (at 90 K). The presence of two types of iron chains with different geometries at 90 K promotes a change in the magnetic properties of these crystals with a decrease in the temperature.
Crystal chemistry of KCuMn3(VO4)3 in the context of detailed systematics of the alluaudite family
Аннотация
The crystal structure of new manganese potassium copper vanadate KCuMn3(VO4)3, which was prepared by the hydrothermal synthesis in the K2CO3–CuO–MnCl2–V2O5–H2O system, was studied by X-ray diffraction (R = 0.0355): a = 12.396(1) Å, b = 12.944(1) Å, c = 6.9786(5) Å, β = 112.723(1)°, sp. gr. C2/c, Z = 4, ρcalc = 3.938 g/cm3. A comparative analysis of the crystal-chemical features of the new representative of the alluaudite family and related structures of minerals and synthetic phosphates, arsenates, and vanadates of the general formula A(1)A(1)′A(1)″A(2)A(2)′M(1)M(2)2(TO4)3 (where A are sites in the channels of the framework composed of MО6 octahedra and TО4 tetrahedra) was performed. A classification of these structures into subgroups according to the occupancy of A sites is suggested.
Na3Tb3[Si6O18] · H2O, a synthetic analogue of microporous mineral gerenite
Аннотация
Crystals of a new silicate, Na3Tb3[Si6O18] · H2O, space group \(P\bar 1\), are obtained under hydrothermal conditions. The formula of the compound is determined in the course of structure solution. The silicate is a synthetic analogue of the gerenite mineral (Ca1.21Na0.57)(Y2.24Dy0.68)Si6O18 · 2H2O, whose structure contains six-membered rings formed by SiO4 tetrahedra. The [Si6O18] rings are connected by TbO6 octahedra into a mixed microporous framework with voids filled by Na atoms and water molecules. The new silicate differs from gerenite by the occupation of the Ca position by Na atoms and population of the pores sandwiched between six-membered rings. By virtue of conditions of hydrothermal synthesis in the absence of Ca and excess of Na in the system, an additional Na position appears in the void. It is populated statistically, and in gerenite it was occupied by water molecules only. In the new structure, the position of water is split into two statistically populated positions. The inclusion of Na atoms in additional positions in framework pores and their high thermal vibrations are indicative of ion-exchange properties of the structure. Possible paths of ion exchange are discussed.
On the existence of declared 9R phase in Fe–Ni invar alloy
Аннотация
An analysis of recently reported electron diffraction patterns suggests that metastable austenitic Fe–32Ni alloy subjected to α → γ transformation upon slow heating does not exhibit any signs of formation of the 9R phase; the conventional nanocrystalline γ phase with an fcc lattice is formed instead. Extended lamellae with a layered structure, erroneously identified as a new phase of the (3R + 9R) type in Fe–32Ni alloy, are conventional twinning (midrib) regions of each initial α crystal, in which γ-phase twin nanolamellae are formed upon heating.
X-ray diffraction studies of the Tl(GaS2)1–x(InSe2)x solid solutions
Аннотация
The unit-cell parameters of crystals obtained in the Tl(GaS2)1–x(InSe2)x system are measured by X-ray diffraction. The relationship between these parameters and composition is determined. It is shown that, with growing x, the a, b, and c parameters increase and the β angle decreases. Two types of solid solutions are found in the Tl(GaS2)1–x(InSe2)x system: one is based on compound TlGaS2 with monoclinic structure and the other is based on TlInSe2 with tetragonal structure.
Structure of Organic Compounds
Crystal and molecular structure of 2,2’-(quinoxaline-2,3-diyl)dipyridinium dinitrate (H2L)(NO3)2
Аннотация
The crystal structure of 2,2’-(quinoxaline-2,3-diyl)dipyridinium dinitrate (Н2L)(NO3)2 is studied by X-ray diffraction (T = 150 K, R1 = 0.0467). The H2L2+ cation is located on the twofold rotation axis and connected with two NO3− anions by strong N–H···O hydrogen bonds. Planar quinoxaline fragments of cations form stacks with the interplanar spacing of 3.308 Å. The structure of the diprotonated H2L2+ cation is compared with those of the monoprotonated H2L2+ cation and neutral L molecule.
Magnetic whiskers of p-aminobenzoic acid and their use for preparation of filled and microchannel silicone rubbers
Аннотация
A thin cobalt layer has been formed on the surface of p-aminobenzoic acid whiskers by chemical vapor deposition (CVD). The metallized crystals have been oriented in liquid polydimethylsiloxane rubber by applying a dc magnetic field. After vulcanization, the filler has been removed by processing in an alcohol solution of trifluoroacetic acid. The cobalt deposition on the surface of the organic compound and the properties of metallized whiskers are investigated by optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM).
Nitrilotris(methylenephosphonato)potassium K[μ6-NH(CH2PO3)3H4]: Synthesis, structure, and the nature of the K–O chemical bond
Аннотация
The crystal structure of nitrilotris(methylenephosphonato)potassium K[μ6-NH(CH2PO3)3H4]—a three-dimensional coordination polymer—was determined. The potassium atom is coordinated by seven oxygen atoms belonging to the six nearest ligand molecules, resulting in distorted monocapped octahedral coordination geometry. The complex contains the four-membered chelate ring K–O–P–O. The K–O chemical bond is predominantly ionic. Meanwhile, the bonds of the potassium atom with some oxygen atoms have a noticeable covalent component. In addition to coordination bonds, the molecules in the crystal packing are linked by hydrogen bonds.
Crystal structure and packing analysis of nitrofurantoin N,N-dimethylformamide solvate
Аннотация
The N, N′-dimethylformamide solvated crystal of the drug nitrofurantoin has been prepared and analysed by single-crystal X-ray diffraction. The two co-crystallized molecules, in the 1 : 1 stoichiometric ratio, are linked by a medium/strong N–H···O hydrogen bond (N···O is 2.759 (3) Å) and a weaker C–H···O interaction to form isolated supramolecular adducts, that in turn are packed into the lattice framework mainly through C–H···O hydrogen bonds. Two-dimensional fingerprint plots of Hirshfeld surfaces are used to visualize, analyze and compare intermolecular interactions found in the title compound and in similar structures.
Synthesis and structure of a 2D Zn complex with mixed ligands stacked in offset ABAB manner
Аннотация
The title complex, {[Zn(ODIB)1/2(bpdc)]·2DMF}n was prepared under hydrothermal conditions (dimethylformamide and water) based on two ligands, namely, 1,1′-oxy-bis[3,5-diimidazolyl-benzene] (ODIB) and biphenyldicarboxylic acid (H2bpdc). ODIB ligands link Zn cations to give layers in crystal. bpdc2– anions coordinate to Zn atoms, however, their introduction does not increase the dimension of the structure. Each layer is partially passes through the adjacent layers in the offset ABAB manner.
Physical Properties of Crystals
Specific features of optical activity in various uniaxial crystals
Аннотация
The influence of the antisymmetric part of the gyration pseudotensor on the characteristics of reflected and transmitted light has been considered for crystals of classes 3, 4, and 6. The results are compared with the corresponding data for crystals of classes 32, 422, and 622 with a symmetric gyration pseudotensor. Specific features of the optical activity in crystals of classes 3m, 4mm, and 6mm with an antisymmetric gyration pseudotensor have been studied. Crystals of classes \(\bar 42m\) and \(\bar 4\) with the symmetric gyration pseudotensor of an unusual form have been considered. The polarization azimuth and ellipticity of the reflected and transmitted light are calculated for these crystals at different angles of incidence.
Influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light in biaxial crystals
Аннотация
The influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light have been investigated for biaxial crystals. Analytical expressions for the optical rotation in the direction of optical axis are obtained with allowance for both the symmetric and antisymmetric parts of gyration pseudotensor. The polarization azimuth and transmitted light ellipticity have been calculated at different angles of incidence.
P-wave ray velocities and the inverse acoustic problem for anisotropic media
Аннотация
The specific features of the calculation of ray velocities of quasi-longitudinal waves in anisotropic media have been considered. A technique for calculating elastic constants using P-wave ray velocities measured in an ultrasonic experiment on spherical samples is presented. It is shown by an example of tabular data that elastic constants С11, С22, and С33 and combinations of constants (С12 + 2С66), (С13 + 2С55), (С23 + 2С44), (С14 + 2С56), (С25 + 2С46), and (С36 + 2С45) can be calculated most accurately for the general case of anisotropic media with elastic properties of arbitrary symmetry. Since the determining system of equations is illconditioned, the values of elastic constants entering these combinations depend on the choosed initial approximation.
Liquid Crystals
On the nature of the orientational effect of ultrasound on nematic liquid crystal
Аннотация
Experimental substantiation of the validity of the model of orientational distortion in a homeotropic layer of nematic liquid crystal under an ultrasonic beam with a sharp boundary is presented for the first time. The model is constructed within the concepts of nonequilibrium thermodynamics and statistical hydrodynamics, taking into account the processes of structural relaxation of the mesophase. It establishes the relationship between the characteristics specifying the homeotropic structure deformation (layer thickness, ultrasound frequency, parameters of the molecular micromodel of liquid crystal, and its material constants) and the layer transparency for a linearly polarized light beam. The calculation results are compared with the experimental data in the frequency range of 0.1–3 MHz.
Surface and Thin Films
Effect of charge memory in organic composites
Аннотация
The effect of charge memory in composites based on polymer molecules has been investigated. Resistive switchings in sandwich samples prepared by lamination from commercially available polymers (polystyrene and poly(2,3-dihydrothieno-1,4-dioxine)-poly(styrene sulphonate) are analyzed. It is shown that the characteristic switching times in the composite samples reach several nanoseconds and the number of switchings exceeds 106. Switchings are observed in electric fields much below the breakdown threshold, which indicates the absence of destructive processes in the polymer.
Nanomaterials
Multilevel description of the DNA molecule translocation in solid-state synthetic nanopores
Аннотация
Interest of researchers in micro- and nanofluidics of polymer solutions and, in particular, DNA ionic solutions is constantly increasing. The use of DNA translocation with a controlled velocity through solid-state nanopores and pulsed X-ray beams in new sequencing schemes opens up new possibilities for studying the structure of DNA and other biopolymers. The problems related to the description of DNA molecular motion in a limited volume of nanopore are considered.
Radiation resistance of endohedral metallofullerenols under neutron irradiation
Аннотация
The endohedral metallofullerenols Me@C2n(OH)38–40 + C2n(OH)38–40 (Me = Tb, Sc, Gd, Fe, Pr, Mo) have been obtained and their radiation resistance under irradiation by a neutron flux of 8 × 1013 cm–2 s–1 has been studied. The factors affecting the radiation resistance of endohedral metallofullerenols are discussed.
Synthesis and radiation resistance of fullerenes and fullerene derivatives
Аннотация
The parameters of an electric-arc facility for the synthesis of fullerenes and endohedral metallofullerenes are optimized. The resistance of С60 and С70 fullerenes and С60(ОН)30 and С70(ОН)30 fullerenols against neutron irradiation is studied. It is established that the radiation resistance of the fullerenes is higher than that of the fullerenols, but the radiation resistance of the Gd@C2n endometallofullerenes is lower than that of the corresponding Gd@C2n(OH)38 fullerenols. The radiation resistance of mixtures of Ме@C2n(OH)38 (Me = Gd, Tb, Sc, Fe, and Pr) endometallofullerenes with C60(OH)30 is determined. The factors affecting the radiation resistance of the fullerenes and fullerenols are discussed.
Crystal Growth
Production of complex rubidium and cesium hydrogen sulfate‒phosphates
Аннотация
The solubility in the CsH2PO4‒CsHSO4‒H2O system at different temperatures (25, 50, and 75°C) is studied and the phase equilibria in the Rb3H(SO4)2‒RbH2PO4‒H2O system under isothermal conditions (at 25°C) are analyzed. The temperature and concentration conditions for forming Rb2(HSO4)(H2PO4), Rb4(HSO4)3(H2PO4), Cs4(HSO4)3(H2PO4), Cs3(HSO4)2(H2PO4), Cs2(HSO4)(H2PO4), and Cs6H(HSO4)3(H2PO4)4 compounds (the latter has been obtained for the first time) are determined. The conditions for growing large single crystals of complex acid rubidium and cesium salts are found.
Synthesis of chalcogenide and pnictide crystals in salt melts using a steady-state temperature gradient
Аннотация
Some examples of growing crystals of metals, alloys, chalcogenides, and pnictides in melts of halides of alkali metals and aluminum at a steady-state temperature gradient are described. Transport media are chosen to be salt melts of eutectic composition with the participation of LiCl, NaCl, KCl, RbCl, CsCl, AlCl3, AlBr3, KBr, and KI in a temperature range of 850–150°C. Some crystals have been synthesized only using a conducting contour. This technique of crystal growth is similar to the electrochemical method. In some cases, to exclude mutual influence, some elements have been isolated and forced to migrate to the crystal growth region through independent channels. As a result, crystals of desired quality have been obtained using no special equipment and with sizes sufficient for study under laboratory conditions.
Apparatus
Calibration of CryojetHT and Cobra Plus Cryosystems used in X-ray diffraction studies
Аннотация
CryoJetHT (Oxford Instruments) and Cobra Plus (Oxford Cryosystems) cryosystems, which are used for sample cooling in X-ray diffraction experiments, have been calibrated. It is shown that the real temperature in the vicinity of the sample differs significantly (the deviation is as high as 8–10 K at low temperatures) from the temperature recorded by authorized sensors of these systems. The calibration results are confirmed by measurements of the unit-cell parameters of GdFe3(BO3)4 single crystal in the temperature range of its phase transition. It is shown that, to determine the real temperature of a sample, one must perform an independent calibration of cryosystems rather than rely on their ratings.