Vol 63, No 1 (2018)

The formation of HfB₂–SiC (10–65 vol % SiC) ultra-high-temperature ceramics by hot pressing of HfB₂–(SiO₂–C) composite powder synthesized by the sol–gel method was studied. By the example of HfB₂–30 vol % SiC ceramic, it was shown that the synthesis of nanocrystalline silicon carbide is completed at temperatures of as low as ≥1700°C (crystallite size 35–39 nm). The production of the composite materials with various contents of fine silicon carbide at 1800°C demonstrated that the samples of the composition HfB₂–SiC (20–30 vol % SiC) are characterized by the formation of SiC crystallites of the minimum sizes (36–38 nm), by the highest density (89%), and by higher oxidation resistance during heating in an air flow to 1400°C.

The synthesis, analysis, and IR spectroscopic, thermogravimetric, and X-ray diffraction study of [Cu(Тsc)₂](Nds) (I), where Тsc is thiosemicarbazide NH₂NHС(=S)NH₂, and 1,5-Nds^2– is the doubly deprotonated 1,5-naphthalenedisulfoacid anion C₁₀H₆(SO₃)₂^2–, have been performed. Crystal structure units in complex I are [Cu(Тsc)₂]²⁺ centrosymmetric complex cations and (Nds)^2– anions (including those in inversion centers). The copper atom is coordinated to the vertices of a square via the two sulfur and two nitrogen atoms of the two bidentate-chelate (S,N) ligands Тsc. Crystal structure units in complex I are linked together by a branched network of weak nonlinear N–Н···О hydrogen bonds with participation of donors (all the five independent hydrogen atoms of the two NH₂ groups and NH group of the [Cu(Tsc)]²⁺ complex cation) and acceptors (all the three independent oxygen atoms of the sulfato group of the 1,5-Nds^2– anion).

A new coordination compound having the formula [La(HMPA)₄(NO₃)₂][Cr(NH₃)₂(NCS)₄] (I), where HMPA is ((CH₃)₂N)₃PO, has been synthesized and studied by X-ray diffraction. Studied crystals of compound I are monoclinic, space group P2₁/n, a = 15.0360(3) Å, b = 15.1214(3) Å, c = 26.7529(7) Å, β = 100.6610(10)°, V = 5977.7(9) Å3, Z = 2, ρ_calc = 1.442 g/cm³, and R₁ = 0.0453 for 7344 reflections with F_o ≥ 4σ(F_o).

[Ph₃PCH₂CH=CHCH₂PPh₃]²⁺[RuCl₄(Dmso)₂]₂⁻ (I) and [Ph₃PR]⁺[RuCl₄(Dmso)₂]^–, where R= CH₂C₆H₄CN-4 (II), CH₂Ph (III), CPh₃ (IV), Ph (V), CH₂OCH₃ (VI) have been synthesized by the reaction between ruthenium(III) chloride hydrate and triphenylorganylphosphonium chlorides in dimethyl sulfoxide (Dmso). According to X-ray diffraction data, the phosphorus atoms in the cations of complexes I–III have a slightly distorted tetrahedral coordination (CPC angles, 105.04(14)°—113.1(2)°); P–C bonds, 1.791(3)–1.829(4) Å). The dimethylsulfoxide ligands in octahedral [trans-RuCl₄(Dmso-S)₂]^– anions are coordinated to metal atoms via sulfur atoms (Ru–S, 2.3279(9)–2.3494(7) Å; Ru–Cl, 2.3202(10)–2.3598(10) Å). The SRuS, cis-ClRuCl, and trans-ClRuCl angles variate within 178.92(4)°–180°, 88.06(4)°–92.81(4)°, and 176.52(4)°–180°, respectively. The crystal structure organization of complexes I–III is formed by hydrogen bonds Н···O_Dmso (2.19–2.66 Å), Cl···Н (2.57–2.93 Å), and N···Н (2.25–2.54 Å).

The structure of carbon nanotubes is described by two positive integers (n₁, n₂). The π-electron model of the nanotube band structure predicts that when the difference n₁–n₂ is multiple of three, the energy gap between the valence and conduction bands vanishes so that such tubes should exhibit quasi-metal properties. The band structure of 50 chiral and achiral (n₁, n₂) nanotubes with 4 ≤ n₁ ≤ 18 and n₂ = n₁–3q has been calculated by the linearized augmented cylindrical wave method. Nanotubes have been identified for which the optical band gaps are in the terahertz range (1–40 meV) and which can be used for design of emitters, detectors, multipliers, antennas, transistors, and other nanoelements operating in the high-frequency range.

The electronic structure of (8,0) gold nanotubes have been studied using quantum field theory methods in the framework of the Hubbard model. An expression for the Fourier transform of the anticommutator Green function, the poles of which determine the energy spectrum of the system under consideration, has been derived. The energy spectrum demonstrates that the (8,0) gold nanotube has metal-like electronic structure. The peaks of the calculated density of states correspond to Van Hove singularities. The optical absorption spectrum is presented, and the energy of the first direct optical transition is 0.55 eV.

Thermal, electrophysical properties, ion mobility, and phase transitions (PT) in compounds (NH₄)₆CsZr₄F₂₃ (I) and (NH₄)₆CsHf₄F₂₃ (II) have been studied by ¹H, ¹⁹F NMR, X-ray powder diffraction, DSC, and impedance spectroscopy. The types of ion motions in the fluoride and ammonium sublattices of both compounds have been determined in temperature range 150–450 K and their activation energy has been assessed. Phase transitions in compounds I and II has been revealed in temperature range 380–404 and 384–412 K to form high-temperature modifications with diffusion of fluoride and ammonium ions as the main type of ion motions. The high ionic conductivity of compounds I and II (higher 10^–4 S/cm at 463 K) allows one to refer these fluoro complexes to the class of superionic conductors.

The stable tetrahedron NaF–KF–KCl–CsCl of the quaternary reciprocal system Na, K, Cs||F, Cl was experimentally investigated by differential thermal analysis. The composition and melting point of the eutectic alloy were determined. The enthalpy of melting of the eutectic alloy was experimentally studied.

By differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements, phase equilibria in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe were studied and their state diagrams were constructed. It was determined that these sections are quasi-binary sections of the eutectic type of the GeTe–Sb₂Te₃–SnTe system. The coordinates of the eutectic points in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe are (40 mol % GeTe, 700 K) and (30 mol % SnTe, 750 K), respectively. Regions of solid solutions based on the initial components in the sections were identified. Alloys in the regions of solid solutions are p-type semiconductors.

Chloroform–water extraction systems have been studied using crown-ethers as extracting agents, namely: benzo-15-crown-5 (B15C5), 2,3-naphtho-15-crown-5 (N15C5), 4′-nitro-benzo-15-crown-5 (NO₂B15C5), 4′-tert-butyl-benzo-15-crown-5 (TBB15C5), and 4′-acetyl-benzo-15-crown-5 (AcB15C5). Extraction isotherms of these systems have been obtained, and an attempt made to elucidate the effect of the structure of extracting agent on extraction characteristics. IR-spectroscopic studies have been performed for selected crown-ethers and their complexes in crystalline form and in chloroform solutions, namely, for N15C5, NO₂B15C5, AcB15C5, and B15C5. The complexes LiN15C5H₂OClO₄ (1), LiN15C5H₂OI (2), LiNO₂B15C5H₂OI (3), LiAcB15C5H₂OI (4), and LiTBB15C5H₂OI (5) have been isolated for the first time and characterized by IR spectroscopy. Single-crystal X-ray data have been obtained for complexes 1–3.

Substitution of chloride ions in AuCl₄⁻ with ethylenediamine (en) and propylenediamine (tn) is studied by capillary zone electrophoresis at I = 0.05 M and T = 25°C. The substitution constants are determined: AuenCl₂⁺ + en = Auen₂³⁺ + 2Cl^–, logK₂ = 10.4; AuCl₄⁻ + tn = AutnCl₂⁺ + 2Cl^–, logK₁ = 16.1; AutnCl₂⁺ + tn = Autn³⁺₂ + 2Cl^–, logK₂ = 12.0.