Inorganic Materials最新文献

We have studied three-dimensional homogeneous and heterogeneous crystal nucleation in and optical properties of stoichiometric lithium disilicate glasses containing silver and/or cerium dioxide additions. The plasmon resonance has been demonstrated on Ag nanoparticles formed under X-ray irradiation.

We have studied the effect of the grain size of aluminum oxide and calcium tungstate on the transport properties of (1 – x)СaWO₄–xAl₂O₃ composites with a mole fraction of aluminum oxide x ≤ 0.35. The phase composition and thermodynamic stability of the composites were ascertained by X-ray diffraction, thermogravimetry, and differential scanning calorimetry. Their surface morphology was examined by electron microscopy and their elemental composition was determined by X-ray microanalysis. The electrical conductivity of the composites was determined by electrochemical impedance measurements and analyzed as a function of temperature, oxygen pressure in the gas phase, dispersoid (aluminum oxide) concentration, and the grain size of their components. The conductivity of the (1 – x)СaWO₄–xAl₂O₃ composites containing 5–10 mol % aluminum oxide was found to exceed that of CaWO₄ by more than one order of magnitude. Varying the average grain size of the Al₂O₃ nanopowder from 21 to 82 nm caused no appreciable changes in the conductivity of the composites, which was due to the polydispersity of the aluminum oxide, whereas reducing the average grain size of CaWO₄ from 6.4 to 1.6 μm led to a twofold increase in the conductivity of the composites.

Eu_1–xSr_xMnO₃ (x = 0.0, 0.25) manganites have been characterized by X-ray diffraction, thermal analysis, and magnetometry. At room temperature, they have a perovskite-like structure, with space group Pbnm. Partial heterovalent substitution of Sr²⁺ for Eu³⁺ cations reduces the Jahn–Teller (JT) distortion of the crystal structure of the manganites because of the decrease in the number of Mn³⁺ ions involved in the distortion mechanism. As the temperature is raised, the europium manganites undergo a transition from an ordered to a disordered state (JT transition), and substitution of strontium for 25% of europium cations lowers the structural JT transition temperature by more than a factor of 4. The manganites undergo a paramagnetic–antiferromagnetic phase transition with a characteristic Néel temperature (T_N). Substitution of Sr for 25% of Eu cations raises T_N from 49 K at x = 0.0 to 65 K.

A ternary molybdate with the composition KSrGd(MoO₄)₃ and a monoclinic scheelite-like structure has been synthesized. Codoping KSrGd(MoO₄)₃ with Er³⁺/Yb³⁺ ions, we have obtained an upconversion phosphor exhibiting anti-Stokes luminescence in the range 400–700 nm under IR excitation. The synthesized phosphor has been characterized by X-ray diffraction, differential thermal analysis, and vibrational spectroscopy, and its luminescence spectra have been measured.

Large-scale practical use of 0D, 1D, and 2D carbon nanomaterials, such as fullerenes, carbon nanotubes, carbon nanofibers, and graphene, depends crucially on the development of techniques for controlled surface modification with the aim of imparting special properties to carbon nanomaterials, which is a key issue in science and technology. This review summarizes various approaches to the preparation of carbon nanomaterials covalently modified by anionic groups with the use of ion beam and plasma treatment processes and considers application areas of such materials in electrocatalysis and electrochemical power sources.

We have studied the effect of mechanical activation on the synthesis of lead indium tantalate and the formation of the perovskite and pyrochlore phases during both mechanochemical synthesis and subsequent firing. To reduce the electrical conductivity of resulting ceramics, lithium carbonate was added to starting mixtures, which is known to stabilize the perovskite structure. PbIn_1/2Ta_1/2O₃ samples were prepared in the presence of 1–3 wt % superstoichiometric lithium carbonate at firing times from 30 min to 2 h. We have found conditions that ensure the preparation of single-phase material with the perovskite structure in the presence of lithium carbonate additions at different firing temperatures. The sequence in which reagents are introduced into the starting mixture and their activation have been shown to have a significant effect on the synthesis of the tantalate and the formation of the perovskite phase. We have compared a number of sample preparation procedures differing in mechanical activation conditions and the way in which the starting materials are introduced. Optimal conditions have been found which ensure the preparation of piezoceramics containing the maximum amount of the perovskite phase and having the highest density.

Hydroxyapatite (HA) and zinc-substituted hydroxyapatite (ZnHA) have been prepared via precipitation from solution. The lattice parameters of ZnHA (а, b = 9.41766 Å, с = 6.88048 Å) are about 0.001 Å smaller than those of HA (а, b = 9.41866 Å, с = 6.88158 Å). The change in the lattice parameters of the ZnHA studied confirms partial Zn²⁺ substitution for Ca²⁺ in the crystal lattice of hydroxyapatite. IR spectra indicated the presence of functional groups (OH^– and ({text{PO}}_{4}^{{3 - }})) in the composition of HA. According to scanning electron microscopy data, the particle size of the ZnHA powder prepared via precipitation followed by heat treatment at 900°C is 200–400 nm. Energy dispersive X-ray microanalysis was used to determine the Ca/P and (Ca + Zn)/P ratios in HA and ZnHA: 1.68 and 1.66, respectively. The solubility of ZnHA in physiological saline was found to be twice that of HA, suggesting good ZnHA resorption in the human body. Tests of disk-shaped samples in SBF solution demonstrated active formation of a new calcium phosphate layer as a result of chemisorption of Ca²⁺, Mg²⁺, ({text{HPO}}_{4}^{{2 - }}), ({text{PO}}_{4}^{{3 - }}), and OH^– ions from solution. ZnHA exhibits activity for both gram positive (Bacillus cereus and Staphylococcus aureus) and gram negative (Escherichia coli and Acinetobacter calcoaceticus) microorganisms.

We have evaluated properties of polyester fabric with coatings based on titanium dioxide and titanium dioxide + silver deposited by magnetron sputtering and compared characteristics of coatings produced by magnetron sputtering and via deposition of sol–gel derived titanium dioxide. A colorimetric method has been used to evaluate the photocatalytic properties of coated polyester fabric and the wear resistance of the coatings. The antimicrobial properties of the coated fabric have been evaluated using a “counting” method.

We have prepared extrapure Ga₁₅Ge₁₀Te_75–xI_x (x = 0–6 at %) glasses with a concentration of 31 impurity elements no higher than 0.2 ppm and studied the effect of iodine on the characteristic temperatures, crystallization resistance, thermal expansion, and density of the glasses. The results have been interpreted in terms of the structural connectivity approach. A technique has been proposed for dynamic dilatometry data processing with the aim of determining the linear thermal expansion coefficient (LTEC) as a function of temperature. The LTEC of the Ga₁₅Ge₁₀Te_75–xI_x glasses has been determined as a function of temperature in the range from 293 to 412 K.

We have synthesized the ternary compounds TlInS₂ and TlGaSe₂ and (TlInS₂)_1–x (TlGaSe₂)_х (x = 0.1, 0.2, 0.4) solid solutions. The phase composition and lattice parameters of their single crystals grown by directional solidification have been determined by X-ray diffraction. At room temperature, the crystals have a layered monoclinic structure with space group (C_{{2{text{h}}}}^{6}left( {C2{text{/}}c} right)). Their properties have been shown to vary systematically with composition. The real (ε') and imaginary (ε″) parts of the complex dielectric permittivity, dielectric loss tangent (tan δ), and ac conductivity (σ_ac) of the single-crystal TlInS₂-based solid solutions have been measured as functions of frequency across the layers of the crystals. Their dielectric properties have been measured by a resonance technique at ac electric field frequencies f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The observed hyperbolic decrease in tan δ with increasing frequency suggests that the solid solutions have conductivity losses. We have identified the hopping mechanism of charge transport in (TlInS₂)_1–x(TlGaSe₂)_х and determined parameters of localized states in the band gap of the crystals: Fermi-level density of localized states (N_F = 5.8 × 10¹⁸ to 1.9 × 10¹⁹ eV^–1 cm^–3), mean hop time (τ = 2 × 10^–7 s), mean hop distance (R = 86 Å), and the energy spread of the states localized in the vicinity of the Fermi level (ΔE = 47 meV). The parameters ε', ε″, tan δ, and σ_ac of the (TlInS₂)_1–x(TlGaSe₂)_х (x = 0.1, 0.2, 0.4) single crystals have been shown to increase with increasing TlGaSe₂ content.