Inorganic Materials最新文献

In this paper, we report a study of the temporal dynamics of photoluminescence intensity in cadmium telluride quantum dots coated with a silicon dioxide shell under continuous optical illumination. Our results demonstrate that at least two mechanisms influence emission from CdTe/SiO₂ quantum dots. In the early stages of our experiments, the luminescence intensity in CdTe/SiO₂ quantum dots is observed to rise, whereas in the final stage luminescence photodegradation begins to prevail. The former mechanism, related to photoenhancement, is due to passivation of surface defects by water molecules and a decrease in the number of nonradiative recombination centers. The latter mechanism, related to photodegradation, can be accounted for by the photooxidation of the CdTe core under the effect of oxygen.

Magnetic hyperfine interactions of ⁵⁷Fe probe Mössbauer nuclei introduced into the ScMnO₃ manganite lattice with a hexagonal crystal lattice have been studied for the first time. Based on the data obtained, the valence state of the probe iron atoms, their local crystal environment, and the orientation of magnetic Fe³⁺ cations in the ({text{ScMn}}_{{{text{0}}{text{.996}}}}^{{{text{57}}}}{text{F}}{{{text{e}}}_{{{text{0}}{text{.004}}}}}{{{text{O}}}_{{text{3}}}}) structure in a magnetically ordered state at T < T_N have been determined. Within the framework of the stochastic relaxation model, the temperature dependence of the Zeeman structure of the ⁵⁷Fe spectra has been analyzed, which has yielded new data on the frustrated Fe−O−Mn exchange interactions. The critical indices of the power-law dependence of the hyperfine magnetic field H_hf(T) on ⁵⁷Fe nuclei have been determined, indicating a reduced dimensionality of the magnetic subsystem of the magnetically ordered manganite ({text{ScMn}}_{{{text{0}}{text{.996}}}}^{{{text{57}}}}{text{F}}{{{text{e}}}_{{{text{0}}{text{.004}}}}}{{{text{O}}}_{{text{3}}}}).

Oxyfluoride glasses in the BaF₂–BaO–SiO₂–B₂O₃–Bi₂O₃–ZnO–Y₂O₃ system were developed and synthesized with various ratios of the initial components. The spectral-luminescent properties of glasses activated with oxides Er₂O₃ and Yb₂O₃ were investigated. According to X-ray powder diffraction, all glass samples are X-ray amorphous, and the glass transition temperature (T_g) was determined. The study of the local structure using IR spectroscopy revealed that the glasses, regardless of composition, contain complex polyborate anions formed by the [BO₃] and [BO₄] groups. It was also shown that bismuth integrates into the glass network, forming Bi–O–Si bonds and network formers in the form of the [BiO₆] groups.

We have studied the dielectric properties of (KNO₃)_1–x/(CeO₂)_x ferroelectric composites with the aim of assessing the effect of cerium oxide on the stability of the polar state of potassium nitrate. The results demonstrate that increasing the fraction of CeO₂ in the (KNO₃)_1–x/(CeO₂)_x composites to 0.25 < x < 0.35 leads to temporary stabilization of their ferroelectric state. The main mechanism of interaction between metal oxides and nitrates is the formation of an electrical double layer on interfaces between particles on account of the difference in adsorption energy between negative and positive ions.

The thermal conductivity of a series of single crystals of Ca_1–x–ySr_xNd_yF_2+y ternary solid solutions containing 0–30 mol % SrF₂ and 10–30 mol % NdF₃ has been measured in the temperature range 50–300 K by an absolute steady-state axial heat flow technique. An increase in the percentage of strontium and, especially, neodymium in the solid solutions is accompanied by a decrease in their thermal conductivity. The temperature dependence of thermal conductivity for all of the solid solutions studied is characteristic of disordered materials.

We have synthesized hydride phases based on a series of TiZrNbTa(Mo_1–xV_x) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) high-entropy alloys with a body-centered cubic lattice. X-ray diffraction characterization results show that, as a result of hydride formation reaction, the cubic lattice of the alloys transforms first into a tetragonal lattice and then into a face-centered cubic one. As the vanadium content of the alloys increases, the fraction of the cubic phase and hydrogen content rise.

In this paper, we examine the purity level and impurity composition of the vanadium, niobium, and tantalum samples in the Exhibition–Collection of Extrapure Substances and present estimates of the average and total concentrations of elemental impurities in the purest samples. We examine the impurity composition of the array of the group 6 elements and contributions of particular groups of impurities and discuss the purity level of the group 6 elements and their compounds manufactured in Russia and abroad.

The effect of the solution acidity on the phase composition and morphology of alumina powers precipitated from solution using Al(NO₃)₃·9H₂O and NH₄HCO₃ was studied. In the рН range of 5–7, an amorphous precursor powder was typically formed; at рН 8–9, NH₄AlCO₃(OH)₂ crystals were formed. When annealed, the powders precipitated from acidic solutions were 100% α-Al₂O₃, which was represented by agglomerated equiaxed particles sized ca. 100–200 nm. The powders prepared in neutral or alkaline solutions, when annealed, formed additional minor θ-Al₂O₃ and γ-Al₂O₃ phases in equiaxed particles sized ca. 20–25 nm.

This paper reports our results on utilization of industrial waste having a multicomponent mineralogical composition and resulting from apatite–nepheline ore beneficiation. Using a high-energy planetary ball mill, the mineral mixture was ground into fine powder. We have studied the process of dispersing the mineral components of the mixture in relation to the main process parameters: vial rotation speed, ball-to-powder weight ratio, and milling time. The results demonstrate that, under “severe” grinding conditions, disintegration of brittle particles of the minerals sphene and aegirine slows down owing to the plasticity of the particles of the minerals apatite and nepheline, which reduces the efficiency of the high-energy grinding process, aimed at reducing the particle size and increasing the specific surface area of the material. The grinding process has been shown to cause not only a reduction in the size of mineral particles, but also changes in their optical properties through amorphization of their surface. This allows mechanically activated powder to be used as a precursor for the preparation of weather-resistant color filler pigments for building and paint materials instead of expensive synthetic analogs.

The specific heat of lanthanum-containing AlMg5.5Li2.1Zr0.15 duralumin-type aluminum alloy has been measured during cooling in the range 300–800 K. We have derived polynomials representing the cooling rates of the lanthanum-containing alloys and a reference. Based on the experimentally determined cooling rates of the alloys and reference and their weights, we have obtained cubic polynomials for the temperature dependence of the specific heat. Using integrals of the specific heat, we derived polynomials for the temperature dependences of enthalpy, entropy, and Gibbs energy changes. The results demonstrate that, with increasing temperature, the specific heat, enthalpy, and entropy of the alloys decrease, whereas their Gibbs energy decreases. The lanthanum content of the alloys has the opposite effect.