Inorganic Materials最新文献

Needlelike and faceted platelike bulk Cd₃As₂ crystals record large in weight (up to 25 g) and size have been grown by chemical vapor transport in a vertical configuration. Mass transport and growth rate calculations based on data on Cd and As₄ vapor partial pressures have been used to optimize experimental conditions. The quality of the crystals was assessed by X-ray diffraction. The single crystals obtained have been used for detailed magnetotransport measurements at temperatures from 80 to 300 K in magnetic fields of up to 1 T. The results demonstrate that the temperature dependence of the resistivity of the grown cadmium arsenide crystals exhibits metallic behavior, with a well-defined linear contribution to their magnetoresistance, whose magnitude reaches 135%/T at 80 K. At the same time, the carrier concentration evaluated by Hall effect measurements proves to be noticeably lower than the level typical of polycrystalline Cd₃As₂. The linear magnetic field dependence of resistivity and the appreciable magnitude of this effect are of practical interest for the use of Cd₃As₂ crystals as materials of magnetic sensors.

Using the TERRA software suite, we have evaluated the adiabatic temperature of reactions of Ta₂O₅ and Mg₄Ta₂O₉ with calcium (2900 and 2362 K, respectively). We have carried out a comparative analysis of the pore structure of niobium and tantalum powders prepared via magnesium and calcium vapor reduction of niobium and tantalum oxide compounds and identified characteristic features of the pore structure of these types of powder. Assumptions are made as to the causes of the formation of the coarser pore structure of the calciothermic powders.

In this paper, we compare mechanical and thermoelectric parameters of Bi₂Te_2.5Se_0.5 alloy prepared via zone recrystallization and extrusion. We have studied the effect of heat treatment on the ultimate strength and thermoelectric figure of merit of an n-type solid solution prepared via extrusion. Its thermoelectric parameters—Seebeck coefficient, electrical conductivity, and thermal conductivity—have been measured at room temperature and in the range 300–430 K, and its thermoelectric figure of merit ZT has been evaluated. The highest 350-K ZT value of the materials prepared via zone recrystallization is 1.0 ± 0.1, whereas the highest ZT value of the materials prepared via extrusion is 0.90 ± 0.1. Heat treatment in a vacuum thermostat at a temperature of 573 K for 24 h increased the highest ZT value of the materials prepared via extrusion to 0.96 ± 0.1 and their ultimate strength to 165 MPa.

The crystal–melt phase transition of a synthesized polycrystalline Ge₂Sb₂Te₅ material (sp. gr. P(bar {3})m1) has been studied using differential scanning calorimetry, thermogravimetry, and temperature-dependent electrical resistance measurements in the range from room temperature to 750°C. Characteristic temperatures of the melting process and the enthalpy of fusion of this material have been determined, and its melting has been classified as a semiconductor–semiconductor phase transition. The conclusion has been made that the predominantly covalent component of interatomic interaction in the crystalline material remains unchanged upon melting.

The tellurium, molybdenum, and zinc complex oxides Te₂MoO₇ and ZnTeMoO₆, promising starting materials for the preparation of zinc-containing tellurite–molybdate glasses, have been synthesized by heating accurately weighed amounts of orthotelluric acid and ammonium heptamolybdate and zinc nitrate crystal hydrates and identified by X-ray diffraction. Using reaction calorimetry, the standard enthalpies of formation of the complex oxides have been determined to be −1412.9 ± 23.7 and −1469.4 ± 23.2 kJ/mol, respectively. These values have been calculated as the difference between the standard enthalpies of solution of the complex oxides and mixtures of constituent binary oxides of corresponding content in concentrated hydrochloric acid and a concentrated sodium hydroxide solution.

The tellurium molybdenum bismuth complex oxides Bi₂Mo₃O₁₂, Bi₆Mo₂Te₂O₂₁, and Bi₂Te₂O₈, promising starting materials for the preparation of bismuth-containing tellurite–molybdate glasses, have been synthesized by heating accurately weighed amounts of orthotelluric acid and ammonium heptamolybdate and bismuth nitrate crystal hydrates and identified by X-ray diffraction. Using reaction calorimetry, the standard enthalpies of formation of the complex oxide have been determined to be −2940.3 ± 39.8 kJ/mol for Bi₂Mo₃O₁₂, −4128.6 ± 66.2 kJ/mol for Bi₆Mo₂Te₂O₂₁, and −1383.3 ± 11.5 kJ/mol for Bi₂Te₂O₈. These values have been calculated as the difference between the standard enthalpies of solution of the complex oxide and mixtures of constituent binary oxides of corresponding content in concentrated hydrochloric acid.

In this paper, we report growth of RAl_2.07(B₄O₁₀)O_0.6 (R = La–Nd) rare earth aluminum dimetaborate single crystals from a K₂Mo₃O₁₀-based fluxed melt. We have studied the composition and thermal properties of the crystals and luminescence spectra of Tb³⁺- and Eu³⁺-doped (Eu,Tb)LaAl_2.07(B₄O₁₀)O_0.6 solid solutions. The results demonstrate that such compounds have a tendency toward gradual decomposition in open systems at temperatures below their melting point. We have identified the mechanism of their decomposition as a function of the nature of the RE cation. The Tb³⁺-doped material exhibits luminescence with a peak emission wavelength of 541 nm, and the strongest Eu³⁺ luminescence peak is located at 613 nm.

AlGaInSbP quinary solid solutions have been synthesized for the first time on InP substrates via temperature-gradient zone recrystallization. We have carried out thermodynamic analysis of the solid solutions, determined their composition, assessed their structural perfection, and measured their photoluminescence spectra. Thermodynamic analysis of the Al_xGa_yIn_1–x–ySb_zP_1–z solid solutions has shown that they have constant lattice parameter in the ranges 0.01 ≤ x ≤ 0.3, 0.0 ≤ y ≤ 1.0, and 0.0 ≤ z ≤ 0.6. In the composition region 0.0 ≤ x ≤ 0.1, 0.0 ≤ y ≤ 1.0, and 0.2 ≤ z ≤ 0.7, the solid solutions are prone to spinodal decomposition. Using linear interpolation methods, we calculated parameters of heterophase equilibria in the Al_xGa_yIn_1–x–ySb_zP_1–z–InP system in the regular solution approximation and located the composition regions of direct (Г₈ → Г₅) transitions (x = 0.1, 0.0 ≤ y ≤ 0.9, and 0.0 ≤ z ≤ 1.0) and indirect (Г₈ → X₅) transitions (x = 0.1, 0.5 ≤ y ≤ 0.9, and 0.0 ≤ z ≤ 0.7). AlGaInSbP epitaxial layers grown at temperatures in the range 773 ≤ T ≤ 973 K, temperature gradients in the range 10 ≤ G ≤ 80 K/cm, and molten zone thicknesses in the range 100 ≤ l ≤ 300 μm had a surface roughness of ~6 nm and high structural perfection (B_H/2 ≈ 10″).

In this paper, we consider modeling of the hydration kinetics of β-CaSO₄⋅0.5H₂O with the use of conductometric measurement results. We review existing kinetic models and use them to describe the results obtained. Stochastic models are shown to ensure the best agreement with experimental data. The practically important result of this study is the possibility of predicting the setting time of gypsum plaster mortars.

We have studied the effect of Yb₂O₃ additions on the phase composition and mechanical properties of Si₃N₄ ceramics and shown that, in all of the samples studied, the Yb₄Si₂O₇N₂ compound was a major component of the grain boundary phase, with ytterbium silicates as minor phases, whose content has been found to increase with increasing Yb₂O₃ concentration in the starting powder mixture. The bending strength of the ceramics has a tendency to decrease with increasing sintering additive content at both room temperature and 1600°C. The load–displacement curves obtained at 1600°C point to plastic deformation and creep of the material, the latter increasing with increasing Yb₂O₃ content, which is due to incomplete crystallization of the grain boundary phase.