Vol 45, No 5 (2019)

The combinatoric and topological analysis and modeling of the self-assembly of the Na₂₆Cd₁₄₁–hP168 crystal structure (space group Pbcm; a = 5.483 Å, b = 24.519 Å, and c = 14.573 Å; and V = 1895 ų) are performed using computational methods (the ToposPro software package). Ninety-eight versions of the cluster representation of the 3D atomic network with the number of structural units ranging from four to seven are found. It is determined that polyhedral clusters–precursors C8 = 0@Na₂Cd₆ and C9 = 0@Na₃Cd₆ are templates, on the surface of which atomic shells consisting of 38 and 41 atoms are formed. The composition of the two-layer clusters is C46 = 0@(Na₂Cd₆)@(Na₁₂Cd₂₆) and C50 = 0@(Na₃Cd₆)@(Na₆Cd₃₅). The centers of clusters C46 and C50 are occupied by positions 1a with the symmetry 6/mmm and 2c with the symmetry −6m2. The symmetry and topology codes of the processes of self-assembly of 3D structures from nanoclusters–precursors C46 and C50 are reconstructed.

Composite materials (CMs) doped with AgI or AgBr and Tb³⁺ or Sm³⁺ ions are synthesized based on matrices of high-silica nanoporous glass (NPGs). The structure of the CMs is studied by IR spectroscopy in the frequency range of 4000 to 400 cm^–1. Bands corresponding to the Ag–O vibrations are found in the IR transmittance spectra of the CMs in the range of 604 to 592 cm^–1. The presence of bands is established, which is associated with the existence of O–Ln–OH, Ln–O–Ln, Ln–O–H, and Ln–O (Ln = Tb, Sm) bonds compared with the NPG and series of materials without rare-earth ions (terbium or samarium). The peaks corresponding to the Ag₂O and Sm₂O₃ oxides are found in the CMs at 940–936 and 640 and 640 cm^–1, respectively.

In this work, the results of the spectral studies of xNa₂O · (100 – x)B₂O₃ · Er₂O₃ (x = 0–45) melts at 1273 K are presented. When increasing the Na₂O concentration in melts the cyclic changes of the coordination numbers of boron atoms are observed. It is shown that the coordination numbers of the Er(III) ions increase from 6 to 8 in the range from 0 to 12 mol % Na₂O.

The glass-forming region in the PbO–GeO₂ system is studied. To increase the glass-forming limit in this system, the tempering rate of the samples has to be increased using special methodological practices. The dependence of the temperature of the synthesis of lead germanate glass on the PbO content is obtained. It is shown that the corrosion of alumina crucibles proceeded during the synthesis of lead germanate glass. The dependence of the thickness of the corroded layer of the alumina crucible wall on the time of the synthesis of the glass of the 55PbO · 45GeO₂ composition, mol % at 900°С is obtained. It is proved that the obtained glass is X-ray amorphous within the whole range of compositions in the PbO–GeO₂ system.

The morphology of monodisperse spherical mesoporous silica particles with a regular pore structure is studied with atomic force microscopy. The size of nanotubes is found: the internal diameter is 2.6 nm, the external diameter is 4.8 nm, and the wall thickness is 1.1 nm. A method for assessing the strength parameters of highly porous materials is proposed. The calculated Young’s modulus of a nanotube along its axis is 91.7 GPa.

New zinc phosphate Li_0.5Na_0.15K_0.85ZnP₂O_6.75 is obtained by the crystallization of a melt and its crystal structure is determined by the single crystal X-ray diffraction data. It is monoclinic and is refined in the space group P2₁/n to R_obs = 0.052; a = 14.609 (7) Å, b = 6.898 (5) Å, and c = 14.603 (7) Å; and β = 118.59 (5)°. The crystal structure is formed by a framework consisting of the PO₄, ZnO₄, and LiO₄ tetrahedra. The ordering of Zn, Li, Na, and K cations and vacancies leads to the formation of a two fold superstructure. The compound belongs to the MM'ZnP₂O₇ structural family, the connection with which is under discussion. The thermal expansion is anisotropic, thus, α₁₁ = 5, α₂₂ = 29, and α₃₃ = 9 × 10⁻⁶°C⁻¹.

Powders–precursors of a tetragonal solid solution based on partially stabilized zirconium dioxide (t-ZrO₂) and aluminum-magnesium spinel (MgAl₂O₄) are synthesized using the method of the cocrystallization of solutions of nitrate salts from which nanocrystalline (<100 nm) composite materials are fabricated at 1400°C in the ZrO₂(Y₂O₃)–MgAl₂O₄ system with an open porosity of 3%. The structure, physical–mechanical properties, and thermal stability of the nanocomposites are investigated. It is established that the introduction of MgAl₂O₄ into the matrix of the solid t-ZrO₂ solution increases the thermal resistance of the ceramics under the thermal cycling conditions (20–1000°С). The effect of thermal cycling on the phase composition, hardness, and bending strength of the ceramics in the ZrO₂(Y₂O₃)–MgAl₂O₄ system is investigated.

The thermal behavior of Na₃H(SO₄)₂ is studied in the temperature range –180...220°C in a pre-vacuum. At 180°C, the compound decomposed into a mixture of phases: Na₂SO₄ (Cmcm), Na₂SO₄ (P6₃/mmc), Na₂SO₄ (Fddd), and Na₂S₂O₇. The maximal thermal expansion was observed near the α₃₃ axis. The anisotropy of thermal expansion sharply decreased together with the increase in temperature.