Vol 63, No 1 (2018)

The possibilities of describing correctly interfaces of different types in solids within a computer experiment using molecular statics simulation, molecular dynamics simulation, and quantum chemical calculations are discussed. Heterophase boundaries of various types, including grain boundaries and solid electrolyte‒solid electrolyte and ionic conductor‒electrode material interfaces, are considered. Specific microstructural features and mechanisms of the ion transport in real heterophase structures (cationic conductor‒metal anode and anionic conductor‒cathode) existing in solid state ionics devices (such as solid-state batteries and fuel cells) are discussed.

The stability of the solution to the problem of restoring the volume size distribution of nanoparticles for theoretical small-angle scattering data sets calculated within six different models has been investigated. The influence of the data noise level on the deviation of the found solution from the specified theoretical model is analyzed. Recommendations on the optimal search scheme of size distributions for complex polydisperse systems are given.

A new method for quantitative description of the degree of similarity of coordination polyhedra has been proposed. The results of studying the five-coordination polyhedra of the antimony and bismuth complexes, in which the nearest coordination environment of metals consists of only oxygen and carbon atoms, have been presented.

Iron-containing Sr₃NbFe₃Si₂O₁₄ single crystals from the langasite family, which are interesting for researchers due to their magnetic ordering at T_N = 26 K, have been grown by the floating zone melting method. Accurate X-ray diffraction analysis is performed at 293 and 90.5 K using the data collected on a CCD diffractometer. To compensate for systematic errors, two data sets are collected at each temperature. The structure is refined based on averaged data set: sp. gr. P321, Z = 1, sin θ/λ ≤ 1.35 Å^–1; a = 8.2609(4) Å, c = 5.1313(3) Å at 293 K and a = 8.2344(6) Å, c = 5.1243(6) Å at 90.5 K; the agreement factors are R/wR = 1.18/1.03% and Δρ_min/Δρ_max =–0.57/0.25 e/Å3 for 3583 independent reflections at 293 K and R/wR = 1.18/1.13% and Δρ_min/Δρ_max =–0.54/0.23 e/Å3 for 3638 reflections at 90.5 K. Negative thermal expansion in the direction of the cell c axis is revealed in the range of 83–110 K.

Crystals of new iodate NaIn[IO₃]₄ were prepared by the hydrothermal synthesis. The unit cell parameters are a = 7.2672(2) Å, b = 15.2572(6) Å, c = 15.0208(6) Å, β = 101.517(3)°, sp. gr. P2₁/c. The formula was determined during the structure determination and refinement of a twinned crystal based on a set of reflections from the atomic planes of the major individual. The refinement with anisotropic displacement parameters was performed for both twin components to the final R factor of 0.050. The In and Na atoms are in octahedral coordination formed by oxygen atoms. The oxygen octahedra are arranged into columns by sharing edges, and the columns are connected by isolated umbrella-like [IO₃]^– groups to form layers. The new structure is most similar to the isoformular iodate NaIn[IO₃]₄, which crystallizes in the same sp. gr. P2₁/c and is structurally similar, but has a twice smaller unit cell and is characterized by another direction of the monoclinic axis. The structural similarity and difference between the two phases were studied by topologysymmetry analysis. The formation of these phases is related to different combinations of identical one-dimensional infinite chains of octahedra.

Succinic acid salts-tris(2-hydroxyethyl)ammonium succinate (C₆H₁₆NO₃)₂⁺ C₄H₄O₄²⁻(monoclinic crystals, sp. gr. P2₁/c, Z = 4) and tris(2-hydroxyethyl)ammonium hydrogen succinate (C₆H₁₆NO₃)⁺C₄H₅O₄⁻ (monoclinic crystals, sp. gr. P2₁/c, Z = 4)—were synthesized and structurally characterized. The specific features of the three-dimensional structures of tris(2-hydroxyethyl)ammonium salts of succinic acid are considered. The role of interionic electrostatic interactions in the structure stabilization and the formation of products of composition 1: 1 and 1: 2 derived from succinic acid is discussed.

Bacterial imidazoleglycerol-phosphate dehydratase from Mycobacterium tuberculosis (HisB-Mt) is a convenient target for the discovery of selective inhibitors as potential antituberculosis drugs. The virtual screening was performed to find compounds suitable for the design of selective inhibitors of HisB-Mt. The positions of four ligands, which were selected based on the docking scoring function and docked to the activesite region of the enzyme, were refined by molecular dynamics simulation. The nearest environment of the ligands was determined. These compounds selectively bind to functionally essential active-site residues, thus blocking access of substrates to the active site of the enzyme, and can be used as lead compounds for the design of selective inhibitors of HisB-M.

Transmission electron microscopy study of ferruginous quartzite (jaspilites) from the Lebedinsky field of Kursk magnetic anomaly has revealed for the first time hematite nanoformations (about 10 nm in size), sp. gr. R3̅, which coexist with hematite, sp. gr. R3̅c, in the same crystallographic orientation or manifest themselves as individual nanoinclusions in the substrate of poorly crystallized magnetite. On the assumption that, in correspondence with the energy-dispersive X-ray analysis data, octahedral sites in the hematite structure can be occupied by only Fe cations, several structural models are proposed explain the hematite symmetry lowering to R3̅.

An X-ray diffraction study of ceramic samples of relaxor ferroelectric (1 – 2х)BiScO₃ · хPbTiO₃ · хPbMg_0.33Nb_0.67O₃ with х = 0.42 in the polarized and depolarized states has been performed. It is established by Rietveld method that in both cases samples contain two perovskite-like phases, which are solid solutions. One of them has cubic symmetry. The second phase is characterized by the polar tetragonal sp. gr. P4mm in the polarized state and the monoclinic noncentrosymmetric sp. gr. Cm in the depolarized state.

TbF₃ (sp. gr. Pnma) crystals up to 40 mm in diameter have been grown from melt by a Bridgman technique. The anisotropy of their mechanical properties is studied for the first time. the technical elasticity constants are calculated, and room-temperature values of Vickers microhardness for the (010) and (100) planes are measured. The shape of indentation impressions is found to correlate with Young’s modulus anisotropy for TbF₃ crystals.

Thermal conductivities of MWO₄ (M = Ca, Cd, or Ba), NaGd(WO₄)₂:1 at % Er, NaGd(WO₄)2:2 at % Yb, and NaLa_0.5Gd_0.5(WO₄)₂:2 at % Nd single crystals have been experimentally investigated in the temperature range of 50–300 K.

The electro-optic effect in three nanoscale heterostructures, in each of which a thin layer of dielectric or ferroelectric material is inserted between two planar metal electrodes, has been studied. Each structure has one aluminum layer, containing a subwavelength grating with a period of 400 nm, contacting with either the glass substrate or air. The light transmission spectra of structures with subwavelength grating contain characteristic plasmon dips. Short external-voltage pulses affect the change in the refractive index of the corresponding active layer. Significant values of these changes may be useful for designing optical modulators.

The ionic conductivity of Sr_0.667R_0.333F_2.333 alloys (rational Sr₂RF₇ compositions) in SrF₂–RF₃ systems (R = Tb or Tm), prepared by spontaneous crystallization, has been investigated for the “as-grown” state and after annealing in CF₄ at 900 ± 20°C for 96 h. As-grown samples of both compositions, prepared by fast (200°C/min) melt crystallization, exhibit partial (nonequilibrium) ordering, which increases from Tb to Tm. Annealing of Sr_0.667R_0.333F_2.333 alloys yields strong ordering (equilibrium for the annealing temperatures) of the fluorite structure (CaF₂ type, sp. gr. Fm3̅m, Z = 4) at the formation of t-Sr₂RF₇ tetragonal compound (sp. gr. I4/m, Z = 30). It is established that ordering of the alloy fluorite structure reduces the fluorine-ion conductivity. After the annealing, the conductivity of Sr_0.667R_0.333F_2.333 alloys with the initial (nonequilibrium) ordering stage of t-Sr₂RF₇ phases with almost complete (equilibrium) ordering decreases by a factor of 3–4.5.

Endohedral metallofullerenes Me@C_2n (n = 30–50), their hydroxylated derivatives Me@C_2n(OH)_38–40 (Me = Tm, Ho, Eu, Sm, Co), and fullerenol С₆₀(OH)₃₈ have been synthesized The radiation resistance of these structures under irradiation in reactor by thermal and fast neutron fluxes in the fluence range of 1018–1019 cm^–2 (cadmium ratio of ~10) has been analyzed. Endofullerenols are shown to be more stable in comparison with initial endohedral fullerenes; the molecules containing Eu and Sm (atoms characterized by the largest slow-neutron absorption cross section) turned out to be most stable. The mechanism of the formation of secondary Eu and Sm endofullerenols is discussed taking into account the neutron capture and emission of γ quanta by excited nuclei, which acquire the recoil energy.

Samples of single-crystal para-quaterphenyl films up to 8 mm long and 50 μm thick have been obtained for the first time by the solvent‒antisolvent growth method. The films have been grown both on the liquid–air interface and in the solution bulk. The morphology, surface quality, and thickness of crystal films have been investigated by the optical, laser confocal, and atomic force microscopies. The structure of the para-quaterphenyl single crystal at room temperature has been refined by X-ray diffraction analysis. The formation and growth mechanisms of crystal films on the liquid–air interface have been discussed. The opticalabsorption and photoluminescence spectra of the solutions and crystal samples have been investigated.