Vol 63, No 10 (2018)

A powdery material Mg(Fe_0.8Ga_0.2)₂O₄ has been prepared by combusting a gel containing magnesium(II), iron(III), and gallium(III) nitrates and a glycine–starch mixture. The gel produced during the synthesis has been studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture has been shown to be efficient to produce a homogeneous nanosized powderlike material Mg(Fe_0.8Ga_0.2)₂O₄. The morphology and properties of ceramic samples are characterized by scanning electron microscopy, X-ray powder diffraction, neutron diffraction, and vibrational magnetometry.

Garnets with the structure similar to that of Ca₃Mn₂Ge₃O₁₂ have been prepared with simultaneous substitutions of Ge⁴⁺ by V⁵⁺ in tetrahedra and of Mn³⁺ by Ni²⁺ or Co²⁺ in octahedra. X-ray photoelectron spectroscopy (XPS) proved the absence of V⁴⁺ in tetrahedra of the lattice of the compounds prepared and determined the valences of elements in octahedral sites. The increasing d-cation size in octahedra is accompanied by an increase in unit cell volume regardless of the composition of tetrahedra (V_yGe_{3 – y})O₁₂. The electrical conductivity of Ca₃Mn_{2 – x}(Ni, Co)_xV_yGe_3–yO₁₂ (x = 0, 1; y = 0, 1, 2) garnet ceramic samples and the calculated bandgap widths make it possible to classify them with medium-gap semiconductors.

Phases of variable composition Ln₃M_{5 – 2x}Ge_{1 + x}Be_xO₁₄ (Ln = La–Gd; M = Ga, Al, Fe, Cr) with the Ca₃Ga₂Ge₄O₁₄ (GGG) structure (space group P321) were prepared by solid-phase synthesis at 1100–1400°С. In Ga systems, GGG phases are formed for La–Eu; in Al systems, for La–Gd; for Fe, only in the La system; and in Cr systems, for La–Sm. Ln₃CrGe₃Be₂O₁₄ compounds have an ordered crystal structure with oxygen octahedra occupied by Cr³⁺ ions. The other phases have an M–Ge–Be disordered structure. The compounds are decomposed in a solid phase and (or) melt incongruently.

Design of composites is a way to improve the quality of solid electrolytes. By mechanically mixing and annealing substituted bismuth vanadate with nanosized aluminum, bismuth, and zirconium binary oxides, we obtained heterogeneous materials Bi₄V_1.7Fe_0.3O_{11 – δ}/xAl₂O₃, Bi₄V_1.7Fe_0.3O_{11 – δ}/xBi₂O₃, and Bi₄V_1.7Fe_0.3O_{11 – δ}/xYSZ. The investigation tools were X-ray powder diffraction and electron microscopy with energy-dispersive microanalysis. The composition of materials was studied, the non-interaction of components was elucidated in the aluminum oxide and zirconium oxide composite series, and a nonuniform distribution of nanopowder particles across the surfaces and cleaves of sinters was discovered. The bismuth atoms from bismuth oxide were shown to be capable of incorporating into the Bi₄Fe_0.3V_1.7O_{11 – δ} structure. The charge transport characteristics of the materials were studied by impedance spectroscopy. No changes were observed in logσ–10³/T trends in composites with various binary oxides and various oxide contents. An increase in binary oxide concentration was shown to give rise to an insignificant decay in electrical conductivity.

The structures of two new coordination polymers, namely, hydroxyl ammonium glutaratouranylate NH₃OH[UO₂(C₅H₆O₄)(C₅H₇O₄)] · H₂O (I) and diethyl ammonium glutaratouranylate NH₂(C₂H₅)₂[UO₂(C₅H₆O₄) (C₅H₇O₄)] · 2H₂O (II), have been characterized by single-crystal X-ray diffraction. It has been established that the structures of complexes I and II contain [UO₂(C₅H₆O₄)(C₅H₇O₄)]–infinite chains with the crystallochemical formula AQ⁰²B⁰¹ (\(\rm{A = UO_2^{2+}}, Q^{02} = C_5H_6O_4^{2-}, B^{01} = C_5H_7O_4^{-}\)). Despite the identical compositions, uranyl glutarate chains in the studied structures appreciably differ from each other by their geometry and linking. The specific features of nonbonded interactions in the structures of complexes I and II have been characterized by the Voronoi–Dirichlet method of molecular polyhedra.

Bis(ethylenediamine-N,N-di-3-propionato)zinc dihydrate [Zn(EDDP)]₂ ∙ 2H₂O is prepared from dichloro(ethylenediamine-N,N-di-3-propionato)zinc in the presence of silver(I) oxide. The prepared complex is studied by X-ray diffraction and spectroscopic methods. A molecule of the complex has a centrosymmetric dimeric structure. Zn atoms have trigonal-bipyramidal coordination formed by the nitrogen atoms of primary and tertiary amino groups, two oxygen atoms of propionic groups of one EDDP molecule, and one oxygen atom of the other.

Hitherto unprepared compounds of composition ABX₂O₇ (where A⁺ and B³⁺ are different cations; and X = P⁵⁺, V⁵⁺, As⁵⁺, Nb⁵⁺, Sb⁵⁺, or Ta⁵⁺) are predicted. Criteria are found to predict the possibility for these compounds to crystalize in one of the crystal structure types (KAlP₂O₇, weberite, NaAlP₂O₇, LiFeP₂O₇, or pyrochlore) at room temperature and atmospheric pressure. The prediction is based only on the properties of elements and simple oxides. The average prediction accuracy is at least 88%. The calculations use an information-analytical system (IAS) comprising precedent-based pattern recognition software.

A new method, which included the sol–gel synthesis of a HfB₂–(SiO₂–C) reactive composite powder and its subsequent consolidation by hot pressing (1700°C, 30 MPa, 15 min) with simultaneous carbothermic synthesis of nanocrystalline silicon carbide, was used to produce HfB₂–SiC ultra-high-temperature ceramic material promising for using in an air atmosphere at temperatures above 2000°C. Its elemental and phase compositions, as well as its microstructure were investigated. The density and calculated porosity were 7.6 g/cm³ and 13.5%, respectively. The behavior of a cylindrical sample of the material was studied on long-term (40 min) exposure to a subsonic dissociated air flow in a high-frequency induction plasmatron. The change in the temperature of the surface of the material was examined in the context of its relationship with the HfB₂ and SiC oxidation and the evaporation of the oxidation products. The phase composition and microstructure were determined in regions of the oxidized surface of a HfB₂–SiC sample containing 30 vol % SiC that were heated on exposure to high-enthalpy flows to 2600–2700°C and in regions the temperature of which was 1850–1950°C. By scanning electron microscopy, the thickness, microstructure, and composition of the oxidized layer were found.

The solubilities and the densities in the aqueous ternary system (MgCl₂ + MgSO₄ + H₂O) at 323.15 K were determined by the isothermal evaporation method. The phase diagram was drawn for this system at 323.15 K. The phase diagram consists of two invariant points, three univariant curves, and three crystallization regions corresponding to bischofite (MgCl₂ · 6H₂O), tetrahydrate (MgSO₄ · 4H₂O) and hexahydrite (MgSO₄ · 6H₂O). Neither double salts nor solid solution was found. Based on the Pitzer and Harvie–Weare (HW) model, the solubility equilibrium constants for the salts were fitted with the solubilities in this research work, and the solubilities of the ternary system at 323.15 K were calculated. Comparisons between the calculated and measured solubilities show that the predicted data agree well with the experimental results.

Extraction of rare earth elements with bis(diphenylphosphorylmethyl) ethers of oligoethylene glycols Ph₂P(O)CH₂O(CH₂CH₂O)_nCH₂P(O)Ph₂ (Lⁿ, n = 0–5) in 1,1,7-trihydrododecafluoroheptanol–water system with variable HNO₃ concentration from 0.5 to 6 mol/L has been studied Complexes of Nd, Eu, Lu, and Er nitrates with L⁰ and L² have been obtained. Crystal structures of [Ln₂L₃⁰(NO₃)₆] · xH₂O (Ln = Nd, x = 1.99; Ln = Eu, x = 1; Ln = Er, x = 6.5; Ln = Lu, x = 6) and [LnL₂(NO₃)₃(H₂O)] (Ln = Nd, Er) have been studied by X-ray diffraction, IR spectroscopy, and thermogravimetry. Correlation between X-ray diffraction and extraction data has been revealed.