Vol 70, No 5 (2025)

The sensory properties of solid solutions of h-Co_xWO₃ (0 ≤ x ≤ 0.09) and h-W_1–xFe_xO₃ (0 ≤ x ≤ 0.06), as well as m-WO₃, were studied in relation to various toxic gases at the maximum permissible concentrations in the air. Doping of h-WO₃ with Co²⁺ or Fe³⁺ ions does not affect the sensitivity of the sensory response to CH₃COCH₃ and NH₃, but leads to a decrease in the sensory signal relative to NO₂. A comparative analysis of the sensory properties of tungsten trioxide of hexagonal and monoclinic crystallographic modification has been performed. When detecting CH₃COCH₃ and NH₃, the sensitivity of h-WO₃ is 1.5 and 1.3 times higher than that of m-WO₃, respectively. The oxygen vacancy concentration and pore volume are key parameters that determine the higher sensitivity of m-WO₃ to NO₂ compared to h-WO₃.

A comparative analysis of ion transfer mechanisms for crystals of three phases with the structures of fluorite (F-phase, CaF₂ and solid solution Ca_1-xHo_xF_2+x), tysonite (T-phase, solid solution Ho_1-yCa_yF_3−y) and orthorhombic modification b-YF₃ (R-phase, HoF₃) in the condensed system CaF₂ – HoF₃ was carried out. Based on the fundamental data on ionic conductivity σ_dc(T), obtained using single-crystal samples in experiments, the dependences “ionic conductivity – composition” and “enthalpy of activation ion transfer – composition” are constructed. A comparison of the properties of the components of the system under study shows that the conductivity of the R-phase of HoF₃ (σ_{500 K} = 5 × 10^-6 S/cm at 500 K) exceeds the conductivity of the F-phase of the stoichiometric composition CaF₂ by 5 orders of magnitude. In the region of the F-phase of non-stoichiometric composition Ca_1-xHo_xF_2+x (0 < x × 0.35) the interstitial mechanism of electrical conductivity is realized. With increasing concentration of HoF₃ the values σ_{500 K} increase, reaching 4 × 10^-5 S/cm at x = 0.35. The conductivity of the non-stoichiometric T-phase Ho_1-yCa_yF_3−y (y = 1−x, x = 0.77) σ_{500 K} = 2 × 10^-4 S/cm exceeds the electrical conductivity of the crystals of the F-phase Ca_0.65Ho_0.35F_2.35 and R-phase HoF₃ by 5 and 40 times, respectively. The reasons for the rapid anionic transfer in the non-stoichiometric T-phase are the vacancy mechanism of electrical conductivity and the wide heterovalent isomorphism of cations.

The solution combustion synthesis obtained precursors of the composition Ni_1–2хMn_хCo_хO_y, where x = 0–0.5. The phase composition of the precursors was confirmed by X-ray phase analysis. The morphology of the samples was studied by scanning electron microscopy in combination with energy dispersion analysis. The change in the phase composition of precursors of mixed d-metal oxides from the synthesis conditions and the choice of annealing temperatures has been studied. The dependences of the content of NiO, Ni, MnCo₂O₄ in the composition of Ni_1–2хMn_хCo_хO_y precursors after SCS, after 550°C were studied. The dependence of the parameter a of the crystal lattice of the spinel phase on the composition of the sample after annealing at 550, 800 and 900°C has been established. Ni_1–2хMn_хCo_хO_y with x = 0.1–0.33 is monophase after annealing at 550°C.

Samples of NASICON glass-ceramics were synthesized by pyrolysis of a mixture of organic solutions in molten rosin. The article discusses the phase formation, morphology and characteristics of the obtained silicophosphates. The composition formed from the precursor with the molar ratio of components Na : Zr : Si : P equal to 3 : 1.33 : 2 : 1 was selected for study. The effect of additional amounts of phosphorus on the phase composition of the sample was studied. It was found that the precursor of the composition 3 : 1.33 : 2 : 1.15 forms densely sintered glass-ceramics containing a crystalline phase of the composition Na₃Zr₂Si₂PO₁₂. The composition of the product is confirmed by the unit cell parameters calculated by the Rietveld method. The samples were obtained at a temperature of 1000 and 1100°С without pressing and have densities of 85 and 88% of the theoretical value, respectively. It was concluded that Na, Si, P not included in the crystal lattice participate in the formation of the X-ray amorphous phase and provide conditions for the formation of NASICON by the type of liquid-phase sintering. A comparative characteristic of the properties of the Na₃Zr₂Si₂PO₁₂ composition obtained from Zr-deficient and non-deficient precursors was carried out. It is shown that the glass phase formed in the intergranular space of Zr-deficient samples negatively affects the conductivity values of the material.

Coordination compounds of rare-earth nitrates with N,N-dimethylacetamide (DMAA), [Sc(H₂O)(DMAA)₂(NO₃)(μ-OH)₂Sc(NO₃)(DMAA)₂(H₂O)](NO₃)₂, [La(DMAA)₄(NO₃)₃], [Ce(DMAA)₅(NO₃)₂][Ce(DMAA)₂(NO₃)₄] and [Ln(DMAA)₃(NO₃)₃] (Ln = Pr, Nd, Sm–Lu, Y), have been synthesized. Using physicochemical analysis methods (elemental analysis, IR spectroscopy, XRD, XRD, TGA-DSC), the compositions and structural features were determined; thermal decomposition of the compounds was studied in a wide temperature range (50–900°C). Complexes [Ln(DMAA)₃(NO₃)₃] form two isostructural series: crystals with Ln = Pr–Dy belong to the monoclinic symmetry, and with Ln = Ho–Lu, Y – to the orthorhombic symmetry. It is shown that the coordination compounds can be used as precursors for the production of nanoscale REE oxides (from 12 to 50 nm) with a specific surface area of 18–65 m²/g.

A series of samples in the Y₂O₃–SnO₂ system with different ratios of yttrium and tin oxides were obtained by solid-phase synthesis. The phase composition of the obtained samples was controlled by X-ray phase analysis. The obtained diffraction patterns were processed and the crystallographic parameters were calculated by full-profile analysis. The conducted study of phase equilibria in the Y₂O₃–SnO₂ system at a temperature of 1400°C made it possible to determine for the first time the homogeneity region of yttrium stannate Y₂Sn₂O₇, which is shifted towards yttrium oxide and is 33.3–36 mol. % Y₂O₃. The existence of a solid solution based on cubic yttrium oxide, extending to 3 mol. % SnO₂, was established. A comparative analysis of the effect of the radius of the substituting tetravalent cation on the width of the homogeneity region of the solid solution based on yttrium oxide was carried out. The absence of solubility of yttrium oxide in tin dioxide was noted.

Titanisation of C/SiC composite fibres with core-shell structure was carried out by synthesis in molten salts. A mixture of salts KCl, LiCl and K₂TiF₆ was used as the reaction medium, and metallic titanum powder was used as the titanising agent. The titanisation was carried out at a temperature of 800°C in a stationary argon atmosphere. Ceramic material was obtained from titanised fibres by hot pressing. The microstructure and phase composition of the fibres and hot pressed samples were investigated. It was found that Ti₅Si₃ and TiC phases are formed during titanation, and during hot pressing the Ti₅Si₃ phase reacts with the carbon core of C/SiC composite fibres to give titanium carbide TiC as a titanium-containing product. It was found that increasing the degree of titanisation leads to a decrease in porosity and an insignificant increase in strength of the obtained material.