


卷 55, 编号 3 (2019)
- 年: 2019
- 文章: 15
- URL: https://journals.rcsi.science/0020-1685/issue/view/9628
Article
A Model for Crystal Growth of Solid Solutions in the InAs–GaAs System by a Modified Floating-Zone Technique
摘要
In this paper, we present a principle and theoretical basis of the growth of single crystals of semiconductor solid solutions by a new modified floating zone technique using seeds consisting of their constituent components. Using a completely homogeneous melt approximation, we find component concentration distributions along the length of InAs–GaAs crystals grown at different process parameters, such as the molten zone length, seed materials, and materials of macrohomogeneous solid solution rods. Analysis of the present results makes it possible to optimize conditions for the growth of single crystals with a preset uniform or graded composition throughout the continuous series of InAs–GaAs solid solutions. We demonstrate the potential of the modified floating zone technique for growing single crystals of semiconductor solid solutions.



Magnetic Properties of FeCr2S4-Based Solid Solutions in the FeCr2S4–CdCr2S4 System
摘要
We have studied the magnetic properties of Cd1 –xFexCr2S4 solid solutions in the FeCr2S4–CdCr2S4 system in the range 0.6 ≤ x < 1. Measurements were made in the temperature range 5–300 K in static (≤7960 A/m) and ac (10, 100, and 1000 Hz) magnetic fields of 79.60 A/m peak. All of the materials have been shown to exhibit low-temperature magnetic anomalies due to the effect of orbital ordering in FeCr2S4, a basic component, at 10 K.



Correlation between the Pycnometric Density and Specific Surface Area of Nanocrystalline VCy Powders
摘要
Nanocrystalline cubic VCy nonstoichiometric vanadium carbide powders differing in nonstoichiometry (0.69 ≤ y ≤ 0.76) and ranging in average particle size from 20 to 60 nm have been prepared by solid-state reactions followed by high-energy milling. Milling of the VCy powders has been shown to be accompanied by changes in their chemical composition, lattice parameter, specific surface area, average particle size, lattice strain, and density. We have derived a relation between the pycnometric density and specific surface area of the VCy powders, which has been used to determine the percentage of oxygen in carbide powder particles and their true density. Oxygen adsorption on the surface of the carbide particles has been shown to be the main cause of the decrease in the pycnometric density of the powders with increasing specific surface area.



Behavior of Some Refractory Hafnium and Tantalum Compounds in Plasma Flows
摘要
By reacting tantalum or hafnium carbide with iridium in the presence of a small amount of silicon, we have prepared refractory hafnium- and tantalum-containing materials consisting of a mixture of phases: the intermetallic compound MIr3, recrystallized tantalum or hafnium carbide, and iridium silicide. We have studied the behavior of the materials during an exposure to a high-speed plasma flow at a sample surface temperature of 2000°C and demonstrated that, owing to their special microstructure, the absence of pores, and the low oxidation rate of the iridium-containing components, they exhibit a good ablation resistance and that the hafnium system withstands a longer exposure.



Synthesis of Highly Dispersed Al2O3–ZrO2–MgO Materials Using Electrogenerated Reagents
摘要
We have studied the morphology and phase composition of precursors for the preparation of highly dispersed alumina-based Al2O3–ZrO2–MgO materials. The precursors were synthesized in a coaxial diaphragmless electrolyzer with a soluble anode. Zr(IV) and Mg(II) ions were added during the synthesis process. It has been shown that varying electrolysis conditions allows the particle size and phase composition of the precipitate to be controlled. Synthesis in the Al2O3–ZrO2–MgO system is accompanied by Al2MgO4 spinel formation. Increasing the spinel concentration helps the metastable phase θ-Al2O3 to persist.



Preparation of High-Purity Aluminum Oxide via Mechanochemical Oxidation of Aluminum in a 0.1 M KOH Solution, Followed by Chemical and Heat Treatments
摘要
We have examined the feasibility of preparing high-purity aluminum oxide by oxidizing granulated aluminum in a 0.1 M potassium hydroxide solution, followed by heat and acid treatments of the oxidation products. The aluminum oxidation product, consisting of two phases of Al(OH)3 (bayerite and gibbsite), was first heat-treated at temperatures of 300, 600, 900, and 1200°C; then treated with hydrochloric acid; and calcined at a temperature of 1450°C. It has been shown that raising the preheat treatment temperature increases the total concentration of impurities, including Fe impurities, but reduces the concentration of alkali metals (K, Na, and Li). Using 99.7%-pure aluminum, we have prepared aluminum oxide with a purity at a level of 99.886%. Using 99.98%-pure aluminum, we have obtained aluminum oxide with a purity at a level of 99.993%.



Synthesis of Fine-Particle α-LiAlO2 via Heat Treatment of a Mechanically Activated Mixture of Gibbsite and Lithium Carbonate
摘要
We have found conditions for the synthesis of fine-particle phase-pure α-LiAlO2 via heat treatment of a mechanically activated mixture of gibbsite and lithium carbonate in air. The results demonstrate that, to synthesize α-LiAlO2, the mechanical activation of the reaction mixture should cause no gibbsite amorphization and heat treatment in air should be performed in the range 650–700°C.



Hydrothermal Synthesis and Characterization of Nanostructured Cobalt-Doped Tin Dioxide
摘要
Nanostructured materials based on cobalt-doped SnO2 have been prepared through alkaline hydrothermal treatment of aqueous solutions of inorganic Sn(II) and Co(II) salts. It has been shown that raising the cobalt concentration to 10 wt % leads to significant changes in the morphology and ferromagnetic properties of the synthesis products. The phase composition of the materials corresponds to tetragonal SnO2 with the rutile structure. Calcination above 450°C leads to Co2SnO4 formation. The saturation magnetization and magnetic susceptibility of the materials vary nonlinearly with the amount of cobalt added to the reaction mixture. The nanostructured material obtained in the presence of ~6 wt % Co has an anomalously high room-temperature saturation magnetization, ~3.5 emu/g, which is almost two orders of magnitude higher than that of highly dispersed powders with a similar composition prepared via chemical precipitation.



Raman Scattering in LiOH and LiOD Polycrystals
摘要
We have studied spontaneous and stimulated Raman spectra of polycrystalline LiOH and LiOD. The observed spontaneous Raman spectra contain low-frequency high-quality-factor lattice modes corresponding to translational and librational oscillations of the ions. The stimulated Raman spectrum has been found to contain several Stokes and anti-Stokes satellites with a large frequency shift.



Structure Formation in the SiO2–Na2O–H2O System during the Fabrication of Foam Glass Ceramics by Extrusion
摘要
This paper presents a method for the fabrication of a foam glass ceramic, an inorganic heat-insulating material, by extruding a mixture of opal–cristobalite rock and a sodium hydroxide solution through calibrated holes. The method ensures excellent mixture homogenization and allows mixing of components and granulation of the mixture to be combined in a single step. As a result of active reactions of amorphous phases in the opal–cristobalite rock with sodium hydroxide in the SiO2–Na2O–H2O system, the average density of the material decreases by a factor of 1.5. This ensures an economic benefit: a proportional reduction in the percentage of sodium hydroxide, an expensive component. Using electron microscopy, we have assessed the effect of temperature on structure formation in the material. The pore formation process begins at 200°C and is accompanied, up to 500°C, by the formation of a loose structure in the form of an inhomogeneous network. In the range 400–500°C, the material undergoes a transition. Above 600°C, a cellular structure begins to form. As a result, the materials synthesized at 850°C have an average density from 0.38 to 0.57 g/cm3 and compressive strength from 3.1 to 5.9 MPa.



On the Visualization of the Magnetoelectric Coupling Region for a Thin Ferromagnetic Layer on a Ferroelectric Substrate
摘要
Scanning electron microscopy results demonstrate that coupling of the ferromagnetic and ferroelectric components in a Co/PbZr0.45Ti0.55O3/Co thin-film structure, resulting in a considerable magnitude (several to tens of mV/A) of a low-frequency magnetoelectric effect at room temperature, extends to a depth of up to 20 μm. This makes it possible to optimize the thickness of the PbZr0.45Ti0.55O3 substrate and enhance the performance of such structures for use as sensing elements in information storage/processing devices and magnetic field sensors based on the magnetoelectric effect.



Synthesis and Thermoluminescence Properties of PbCd2 –xMnxB6O12 Solid Solutions
摘要
Powders of the double borate PbCd2B6O12 and PbCd2 –xMnxB6O12 solid solutions have been prepared by solid-state reactions and the crystallographic characteristics of the synthesized phases have been determined (sp. gr. P21/n). Using differential scanning calorimetry and X-ray diffraction, the PbCd2B6O12 compound has been shown to melt incongruently at 734°C. The effect of activator ion concentration on the thermoluminescence intensity in phases of variable composition at temperatures in the range 25–400°C has been studied for the first time. The sample containing 5 mol % Mn2+ ions has been shown to offer the highest luminescence brightness in the visible spectral region.



Mechanochemical Activation of Precursor Powders for the Preparation of Dense Al2O3–ZrO2〈Y2O3〉 Nanoceramics
摘要
A process has been demonstrated for the preparation of precursor powders and nanocrystalline (60–90 nm) alumina-based ceramics in the Al2O3–ZrO2〈Y2O3〉 system. We have studied the influence of mechanochemical activation (MA) on the structure and particle size of precursor powders and found the most effective MA time. MA has been shown to lower the α-Al2O3 formation temperature and accelerate the powder sintering process. We have optimized powder consolidation conditions for the fabrication of dense nanoceramics and studied their physicochemical and mechanical properties.



Effect of Strain on the Formation of a MAX Phase in Ti–Al–C Materials during Self-Propagating High Temperature Synthesis and Extrusion
摘要
This paper presents numerical modeling results and experimental data on thermal conditions in Ti–Al–C MAX phase-based materials during self-propagating high-temperature synthesis (SHS) and extrusion. Based on a mathematical model for the thermal conditions of SHS extrusion, which makes it possible to analyze longitudinal and radial temperature profiles in an extruded sample with a model composition (64.2 wt % Ti + 27.1 wt % Al + 8.7 wt % C), we make recommendations as to favorable conditions for MAX phase formation in relation to strain, predict such conditions, and qualitatively compare the theoretical results and experimental data. We examine the effect of the delay time before compaction on the surface defect density of the samples and the effect of strain on the structure and surface quality of the extruded materials. Samples 10 mm in diameter are shown to be free of titanium carbide, whereas samples 5 and 8 mm in diameter contain 6–8 wt % titanium carbide.



Synthesis of Nanostructured Sodium Aluminosilicate from Rice Straw and Its Sorption Properties
摘要
We have demonstrated the possibility of preparing nanostructured, X-ray amorphous sodium aluminosilicate with a specific surface area of 364 m2/g using an alkaline rice straw hydrolysate. Its Cs+ sorption properties have been studied under static conditions in solutions with various salt compositions (seawater and nitrate solutions).


