Vol 62, No 3 (2017)

A promising yellow phosphor, α-Zn₂V₂O₇, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO₄ tetrahedra.

Nanopowders La_1–xZn_xFeO₃ (nominal degree of doping x_nom = 0, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, and 0.4) were synthesized by the sol–gel method using aqueous ammonia as a precipitator and were then annealed at 950°C for 60 min. From the data of X-ray powder diffraction analysis and local electron probe microanalysis, the maximum actual limit of doping of lanthanum ferrite with zinc was determined: x = 0.072. The dependence of the particle size on the Zn²⁺ content was found to be nonmonotonic. The magnetic characteristics (specific magnetization J, coercivity H_c, and magnetic susceptibility χ) of samples at temperatures of 300 and 100 K in fields of up to 1300 kA/m. It was shown that, with increasing degree of doping, J increases from 0.188 A m²/kg (at x = 0) to 0.245 A m²/kg (at x = 0.072), and χ varies nonmonotonically from 11.5 × 10^–6 (at x = 0) to 15.3 × 10^–6 (at x = 0.072) (at 300 K). With decreasing measurement temperature to 100 K, the magnetization and susceptibility monotonically increase.

The mesomorphic properties of cholesteric ester of p-nitrobenzoic acid С₃₄Н₄₉NO₄ were studied by differential scanning calorimetry and polarizing thermomicroscopy. Its thermal stability was determined using TGA data. The molecular and crystal structures were characterized by single-crystal X-ray diffraction. Crystals were monoclinic, а = 10.7023(4) Å, b = 10.0995(4) Å, с = 14.1563(6) Å, β = 101.499(1)°, space group Р2₁, Z = 2. An extensive molecule contained three different structural moieties: p-nitrobenzoic acid moiety, a cholesteric core consisting of four conjugated rings of different conformation, and a hydrocarbon chain of six carbon atoms. A molecule was chiral and “left” with a torsion angle of 2.6°.

Comparison of tetrabenzoporphyrin complexation reactions and transmetalation of cadmium(II) tetrabenzoporphyrinate with cobalt(II) acetate and chloride in dimethylformamide (DMF) has been carried out Cobalt(III) tetrabenzoporphyrinate has been prepared and identified. Acido ligands displacement in Co(III) tetrabenzoporphyrinate by pyridine, imidazole, and quinuclidine molecules has been studied.

The successive elimination of Н₂ from NaBH₄ ∙ 2Н₂O, (NaBH₄ ∙ 2Н₂O)₂, (NaBH₄ ∙ 2Н₂O)₄, and (NaBH₄ ∙ 2Н₂O)₄ · Н₂O complexes has been modeled in the framework of the cluster approach with the use of the 6-31G* basis set and hybrid density functional (B3LYP). Computations show that combination of NaBH₄ ∙ 2Н₂O into clusters and addition of one water molecule lead to a decrease in potential barriers to elimination of molecular hydrogen to 0.8–0.9 eV. Transformation of two OH groups of the В(OН)₄^- anion to give a В=O double bond with elimination of water molecule in the tetramer (NaB(OH)₄)₄ has been considered.

First-principles calculations based on density functional theory (DFT) are used to study the chemisorption properties of one, two, and four hydrogen atoms on the zigzag and armchair single-walled InN nanotubes (InNNTs).The results indicate that the H atom is strongly bounded to the exterior wall of (4, 4) InNNTs compared with the (7, 0) InNNTs, while the chemisorption energies corresponding to the most stable configuration of H₂ dissociation and a single H atom are found to be–3.85 and–3.26 eV, respectively. Furthermore, the effect of the hydrogen storage on the geometries and electronic properties of related InN nanotubes were also discussed. The computed density of states (DOS) indicates that the energy gap of the zigzag and armchair InN nanotubes on hydrogen adsorptions are significantly decreased which can increase the electrical conductance of the tubes. Therefore, InN nanotubes due to the high binding energy can be used for hydrogen storage.

A relationship between the energy and length of a covalent bond is derived from the theory of generalized charges, the asymptotic approximation of quantum mechanics for interatomic forces, which relies upon the model of multicomponent electron gas. The new relationship for the ground state of diatomic molecules is obtained in the form of analytical expressions without empirical coefficients; characteristics of electronic configuration are its parameters. Fairly good agreement between the results of a priori calculations and the experimental data for various molecules is demonstrated.

The results of studying the binuclear copper(II) complexes with acyldihydrazones of amino-, oxo-, and thiodiacetic acids and 2-hydroxyacetophenone were described. The temperature variations of the EPR spectra of solutions with a seven-line hyperfine structure indicating an exchange character of interaction between unpaired electrons and the two equivalent nuclei of copper atoms were studied.

Temperature-dependent magnetization was measured for CuCr_2–xSb_xSе₄ solid solutions in the range 300–5 K in a weak field (50 Oe) and a strong field (10 kOe) and in an ac magnetic field having a frequency of 100–10000 Hz and an amplitude of Н = 1 Oe. The type and character of magnetic transitions under investigation in the system were determined, and its magnetic phase diagram was constructed.

We show the feasibility to prepare a disperse Fe–Al–Mo polymetal system by contact exchange in chloride-containing aqueous solutions. Reaction schemes are suggested to describe the processes that proceed on aluminum microparticles in aqueous solutions where the relevant metal ions are contained. The system is shown to be a precursor for intermetallic compounds, which are generated by high-temperature processes, e.g., spark plasma sintering (SPS).

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.