Том 44, № 2 (2018)

A search for crystal structures of A_nO_m metal oxides containing icosahedral i–A@A₁₂ cluster precursors is performed (TOPOS program package, ICSD and CRYSTMET databases). Among 1802 metal oxides, the local region represented by i–Cs@Cs₁₂ is determined in the Cs₇O (P-6m2) metal oxide. In the case of the (Rb₁₃)(Rb₂O)₃ (Fm-3c, cF184, V = 12409.8 ų) metal oxide, the i–Rb@Rb₁₂ cluster precursor with the symmetry m-3 and cluster spacers in the form of Rb–O–Rb chains, which occupy the pores in the threedimensional framework, are identified. Cluster i–Rb@Rb₁₂ occupies position 8b with the highest possible crystallographic symmetry m-3 for icosahedron. The topological type of the basic 3D network, which characterizes the packing of cluster precursors Rb₁₃, corresponds to a simple cubic 3D network P_c (Pm-3m, cP1) with CN = 6. The symmetric and topological codes of the self-assembly processes of the crystal structure from the nanocluster precursors S₃⁰ is fully reconstructed in the following form: primary chain S₃¹→ microlayer S₃²→ microframework S₃³. Cluster precursors in the primary chain are flipped through 90° and are characterized by the maximum possible number of Rb–Rb bonds corresponding to 8 and this mechanism of local binding is realized at all stages of the self-assembly of the 3D framework structure. During the assembly of the primary chain and microlayer, there is additional binding of the Rb@Rb₁₂ icosahedra via the Rb atoms of three-atomic cluster spacers Rb–O–Rb. In the 3D framework structure, in the local environment of Rb@Rb₁₂, there are 12 Rb–O–Rb cluster spacers.

The structure of borosilicate glasses is studied with ¹¹B and ²⁹Si NMR spectroscopy in order to investigate the influence of replacement of Na₂O by oxides of alkali earth metals on their local structure. The quantitative data are analyzed with respect to their correspondence to the criterion of the average charge of the structural unit. The reasons for the deviation between the experimental results and this criterion are considered. It is shown that, in the case of glass devoid of borate structural units with nonbridging oxygen atoms, the corrected contents of these units are consistent with the predictions of thermodynamic modeling of the structure and properties of oxide glasses.

The ion-exchange interaction of the sodium aluminosilicate and sodium galliumsilicate melts with a mixture of molten Li, Na, K, Rb, Cs, and Ba chlorides is studied. It is established that two alkaline silicate melts are characterized by negative deviations from the ideal behavior, and silicate melts containing alkaline and alkaline-earth cations are characterized by noticeable positive deviations from the ideal behavior.

Layered ceramics based on bismuth–calcium cobaltite with varied cobalt oxide contents is synthesized by the solid-phase method, the ceramics phase composition is determined, and the microstructure, thermal expansion, electroconductivity, and thermal electromotive force are investigated. The formation of just one compound, ternary oxide composed of Bi₂Ca₂Co_1.7O_y, is established within the quasi-binary Bi₂Ca₂O₅–CoO_z system. The effect of the cobalt oxide content on the Bi₂Ca₂Co_xO_y ceramics’ microstructure and physicochemical properties is analyzed. The single-phased ceramic sample Bi₂Ca₂Co_1.7O_y demonstrated the highest power factor value among all the investigated samples—26.0 μW/(m K²) at a temperature of 300 K. This sample showed the lowest value of the thermal linear expansion coefficient of 9.72 × 10^–6 K^–1.

The possibility of synthesizing protonated derivatives of layered perovskite-like titanates Bi₄Ti₃O₁₂, ABi₄Ti₄O₁₅, (A = Ba, Sr, Ca) and K_2.5Bi_2.5Ti₄O₁₃ is experimentally investigated. It is established that in the case of Bi₄Ti₃O₁₂ and ABi₄Ti₃O₁₅, single-phased protonated derivatives cannot be obtained by treating the compounds with acid solutions, due to the partial dissolution of initial oxides, accompanied by the formation of titanium dioxide. In the case of K_2.5Bi_2.5Ti₄O₁₃ titanate, a number of new protonated and hydrated derivatives are obtained and described.

The problems of using metallic glasses for fabricating magnetic cores of cryogenic and superconducting electrotechnical devices, operating at low temperatures of 77 K, are considered. The experience of creating a number of devices, including electric generators, motors and transformers with HTSC windings, is analyzed. The advantages and disadvantages of magnetic cores from annealed tapes are considered. The results of the study of losses and magnetic characteristics of domestic amorphous and nanocrystalline alloys before and after high-temperature annealing are presented.

The phase separation and the emergence of nanocrystalline inclusions in phosphate–silicate preforms for optical fibers activated with ytterbium, which are obtained by the powder sintering methods with the vibrational mixing of the melt and the addition of ytterbium-containing nanoparticles into preforms, are studied. Nanocrystals of YbPO₄, SiO₂, and YbP₃O₉ are formed in the preforms in the low-temperature areas of the powder sintering process when using either of the methods. It is concluded that the phosphates are crystallized as a result of the phase separation from the glass phase enriched with ytterbium.

Foamed glass samples based on a glycerol pore-forming mixture at varied temperatures are synthesized. The structure and properties of the samples are investigated. The effect of varying the glycerol content on the structure and properties of the samples is determined. The optimal ratio of the components of the mixture for synthesizing foamed slag glass is revealed.