Modeling of nonlinear processes of nucleation and growth of GaSxSe1–x(0 ≤ х≤ 1) solid solutions

The results on the study of modeling and physico-chemical study of the kinetics ofnucleation and growth of GaSxSe1–x(0 ≤ х≤ 1) solid solution. The nucleation heterogeneous process and growth of GaSxSe1–xcrystals have been studied and simulated taking into account nonlinear equations considering the kinetic behavior of crystallizing phases.GaSxSe1–xsingle and nanocrystals were grown from solution, melt, and by chemical transport reaction through steam. GaSxSe1–xcrystals were grownbychemical transport reaction in a two-tem-perature gradient furnace in a sealed quartz ampoule. Iodine was used as a transporting additive. Using the Fokker–Planck equation, the evolution of the distribution function of crystals of solid solutions of the GaS–GaSe system by size at the nucleation time is studied by a numerical method. For the convenience of comparing theory with experimental data, we used the GaS1–xSex(x= 0.7 molar fraction of GaSe) composition of the solid solution. The Monte Carlo method is used to approximate the time evolution of the nucleation of two types of particles for the GaS0.3Se0.7 solid solution, simulated by a constant nucleus size. The results of modeling non-linear crystallization processes are consistent with experimental data.

Sublimation of Li@C60

Experiments that probe the fundamental properties of endohedral fullerenes often require the preparation of molecular beams or thin films of the neutral molecules. It is challenging to cleanly sublime this class of molecules without producing some thermal degradation. We report combined gas phase and scanning tunnelling microscopy studies that probe the thermal decay of commercial [Li+C60]PF6- in a quartz ampoule and provide treatment conditions that will allow the sublimation of intact, neutral Li@C60 accompanied by a well-characterised component of neutral C60. The decay of the material at appropriate temperatures can be modelled with the assumption of a second order decay process in the oven yielding Arrhenius parameters that can predict the ratio of Li@C60 to C60 in the sublimed material. Graphical abstract

Single crystal investigation of the YbAl2 compound

A sample of nominal composition Yb33,3Al66,7 was synthesized from high-purity elements (Yb ≥ 98.9 wt.% and Al ≥ 99.999 wt.%) by arc-melting under a purified argon atmosphere, using Ti as a getter and a tungsten electrode. To achieve high efficiency of the interaction between the components, the sample was melted twice. The ingot was annealed at 500°C in an evacuated quartz ampoule for 720 h and subsequently quenched in cold water. The weight loss during the preparation of the sample was less than 1 % of the total mass, which was 2 g. The chemical composition of the selected crystals was checked with a field-emission scanning electron microscope (FEINovaNanoSEM 230) equipped with an EDS analyzer. Laue and rotation diffraction patterns of selected single crystals showed cubic symmetry. Integrated intensities measured with graphite-monochromatized Мо Kα radiation (l = 0.71073 Å) on an Xcalibur Atlas CCD diffractometer confirmed the cubic lattice. The structure type MgCu2 was assigned and the structure was refined using the program SHELXL (full-matrix least-squares refinement on F2)] with anisotropic displacement parameters for all of the atoms: Pearson symbol cF24, space group Fd-3m, a = 7.7011(4) Å, V = 456.73(7) Å3, Z = 8, R = 0.0261, Rw = 0.0726 for 42 reflections. It is well-known that the trivalent state is usual one for the rare earth metals. The dependence of the mean atomic volume of the RAl2 binary showed of the so-called “valence” fluctuation state for Eu and Yb.

Crystal structure and chemistry of tricadmium digermanium tetraarsenide, Cd3Ge2As4

A cadmium germanium arsenide compound, Cd3Ge2As4, was synthesized using a double-containment fused quartz ampoule method within a rocking furnace and a melt-quench technique. The crystal structure was determined from single-crystal X-ray diffraction (SC-XRD), scanning and transmission electron microscopies (i.e. SEM, STEM, and TEM), and selected area diffraction (SAD) and confirmed with electron backscatter diffraction (EBSD). The chemistry was verified with electron energy loss spectroscopy (EELS).

Facile synthesis of novel antimony selenide nanocrystals with hierarchical architecture by physical vapor deposition technique

Stoichiometric antimony selenide (Sb2Se3) nanocrystals have been successfully engineered by a facile physical vapor deposition method, employing a single precursor of polycrystalline Sb2Se3 charge in a closed quartz ampoule under high vacuum without any foreign seed or extraneous chemical elements. This work underscores the efficacy of the vapor deposition process and provides synthetic strategies to scale down bulk Sb2Se3 into novel nanostructures. The morphological evolution of the tailored architecture was examined on micro and nano size scales by scanning electron microscopy and high-resolution transmission electron microscopy. The intrinsic mechanism governing the nanostructure formation is revealed as layer-by-layer growth, related to the unique layered structure of Sb2Se3. The optical properties of the grown crystals were probed by UV–vis–NIR and photoluminescence tools. The band-gap values of the microfibers, nanorods, nanooctahedra and nanospheres estimated from UV–vis–NIR analysis are found to be 1.25, 1.47, 1.51 and 1.75 eV, respectively. Powder X-ray diffraction, energy-dispersive analysis by X-rays, X-ray photoelectron spectroscopy, Raman spectroscopy and photoluminescence studies confirmed the quality, phase purity and homogeneity of the as-grown nanostructures. The adopted physical vapor deposition method is thus shown to be a simple and elegant route which resulted in the enhancement of the band gap for the Sb2Se3 samples compared with their counterparts grown by chemical methods. This approach has great potential for further applications in optoelectronics.

Study of melting and crystallization process of CsPbBr3 by differential thermal analysis

The crystalline CsPbBr3 was synthesized from CsBr (6N) and PbBr2 (5N) by the mechanochemical method with further fusion in quartz ampoule at 640-650 °С. After synthesis, the structure and chemical composition of the obtained material was confirmed by energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis. The melting and crystallization of the obtained perovskite were investigated by the differential thermal analysis (DTA) with heating/cooling rates of 1, 5 and 10 °C/min. Measurements were carried on the self-constructed DTA-setup with S-type thermocouples in the range of 450-590 °C. Each cycle of heating/cooling was repeated three times to confirm the accuracy of the results obtained. A decrease in the melting point from ~ 568.1 °C to ~ 566.2 °C was demonstrated with an increase in the heating rate from 1 °C/min. up to 10 °C/min. respectively. Probably, it's due to the approach to equilibrium conditions of phase transformations at lower heating rates. We recorded an additional-endothermic effect during CsPbBr3 melting. This may indicate a complex process of melting the compound. The thesis of a two-stage melting mechanism of CsPbBr3 perovskite with an initial stage of fragmentation of the crystalline structure and subsequent dissolution of crystalline phase residues is proposed. It is reported that with increasing of the melt heating above a certain "critical" temperature (579-585 °C), its homogenization occurs, and the crystallization temperature is set at 540-550 °C for the heating/cooling rate of 1 ° C/min. and 538-543 °C for the rate of 5-10° C/min. All obtained data confirm the assumption of a two-step melting process of CsPbBr3 perovskite, and the relatively constant crystallization temperature after a critical point of overheating may also indicate a certain structure of the melt of the compound with short-range order in the arrangement of the structural units of the compound in the liquid phase.

Structural and optical properties of AgIn5S8

Compounds of the chalcogenide family Ag–In–VI (VI = S, Se, Te) are interesting materials due to their stoichiometric stability and potential application in nonlinear optics and solar cells. A polycrystalline ingot of AgIn5S8, an ordered vacancy semiconductor, was prepared by direct fusion of the stoichiometric mixture of the elements in an evacuated quartz ampoule. The presence of a single phase with cubic structure was confirmed by X-ray powder diffraction at room temperature. The lattice parameter, [Formula: see text], was calculated, giving 10.821750 Å. Samples in evacuated quartz ampoules were used to perform Differential Thermal Analysis measurements, showing congruent melting at 1110[Formula: see text]C. Transmittance and reflectivity measurements were used to calculate the absorption coefficient [Formula: see text]. From the plot of ([Formula: see text])2 versus [Formula: see text], two direct transitions are observed at 1.25 eV and 1.88 eV. While the higher energy direct transition has been observed by other authors, the direct nature of the lower energy transition was confirmed from the fitting of the plot of the reflectivity versus 1/[Formula: see text] between 0.53 eV[Formula: see text] (1.89 eV) and 0.55 eV[Formula: see text] (1.82 eV), obtaining a value of 1.29 eV. The real refractive index [Formula: see text] and the high-frequency dielectric constant [Formula: see text] were also obtained from the fit of the reflectivity, resulting to be 2.68 and 7.2, respectively.

PHASE EQUILIBRIUM IN YbTe–Yb3Ge5 SYSTEM

For citation:Mukhtarova Z.M. Phase equilibrium in Ybte–Yb3Ge5 system. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 64-67.Study of properties of semiconductors developed in close connection with their technical applications. The present work was devoted to study of phase equilibria and character of interaction in YbTe–Yb3Ge5 system. The section of YbTe–Yb3Ge5 in ternary system Ge–Te–Yb is not only scientific, but also practical interest. The section of YbTe–Yb3Ge5 was studied by methods of physical-chemical analysis: differential-thermal (DTA), high temperature differential-thermal (HTDT), X-ray phase, microstructural analysis (MSA), as well as measurement of density and micro hardness. DTA was performed with pyrometer HTP-75 in quartz ampoule pimped off till 0.1333 Pa. HTDT was performed with HTDT-8m (Tmelt.≥1500÷2000K) by analogical method. X-ray phase analysis was performed by powder method with X-ray diffractometer DRON-2 (CuKα- radiation with Ni-filter). MSA was performed with microscope MIM 8. Micro hardness of alloys was measured with micro hardness tester PMT-3.Density of alloys was determined by pycnometer test. During investigations of the system we used germanium B–4, tellurium B–3, ytterbium Yb–1. Alloys were synthesized at 1450–1700 K temperature range and at this temperature ampoule was kept 5–6 h. Cooling was performed slowly. DTA shows that on thermograms of alloys of the system have two effects. Obtained effects are endothermic reversible.For confirming the data of DTA, microstructural analysis, as well as measurement of micro hardness were performed with X-ray analysis. As the data show, at the concentration of 15–80 mol% of Yb3Ge5 monotectic conversion occurs which is confirmed with isothermal line at 1025 K. Thus, it was established that the section of 4YbTe–Yb3Ge5 is quasibinary cross-section of ternary system Ge–Te–Yb and its diagram is related to eutectic type with monotectics.Eutectic of the system 4YbTe–Yb3Ge5 corresponds to composition of 85% mol% of Yb3Ge5 and temperature of 915 K.

The diffusion coefficients 110mAg isotope in copper-contained chalcogenide films obtained by chemical deposition

Методом химического нанесения из растворов халькогенидных стекол в н-бутиламине получены многокомпонентные халькогенидные пленки CuI-As2Se3, CuI-PbI2-As2Se3, CuI-SbI3-As2Se3, CuI-SbI3-PbI2-As2Se3. Синтез многокомпонентных медьсодержащих халькогенидных стекол, использовавшихся для нанесения пленок, проводили методом вакуумной плавки в кварцевых ампулах при температуре 400…950 °С и остаточном давлении не более 0,13 Па. Закалку стекол производили от 600 °С в воду со льдом с разливом расплава в ампуле. Навеску стекла размельчали в порошок и кипятили в н-бутиламине до полного растворения. Для предотвращения процессов окисления, нанесение и отжиг пленок проводили в атмосфере химически инертного азота. Подложку помещали на устройство для вращения, наносили на нее раствор и вращали подложку со скоростью несколько тысяч оборотов в минуту. Отжиг пленок проводили при температуре 100 °С в течение 1 ч. Измерение электропроводности полученных пленок проводили на постоянном и переменном токе в зависимости от значений электропроводности в температурном интервале 20…100 °С. Измерение коэффициентов диффузии проводили абсорбционным методом. Из диффузионных экспериментов определены значения коэффициентов диффузии катионов изотопа 110mAg в медьсодержащих халькогенидных пленках. Установлено, что значения коэффициентов диффузии ионов Ag+ в химически нанесенных пленках и исходных стеклах практически не различаются. Аналогию значений коэффициентов диффузии изотопа 110mAg в халькогенидных стеклах и пленках на их основе можно объяснить сохранением полимерной сетки связей халькогенидных стекол при их растворении в органических основаниях (аминах). В процессе нанесения и формирования пленок полимерная (макромолекулярная) структура раствора халькогенидных стекол сохраняется. The method of chemical deposition from solutions of chalcogenide glasses in n-butyl amine obtained multicomponent chalcogenide films CuI-As2Se3, CuI-PbI2-As2Se3, CuI-SbI3-As2Se3, CuI-SbI3-PbI2-As2Se3. Synthesis of copper multicomponent chalcogenide glasses, used for film deposition was carried out by vacuum melting in quartz ampoule at a temperature of 400…950 °C and a residual pressure of not more than 0.13 Pa. The temperature of glass produced from the 600 °C to the ice water spill of the melt in the ampoule. Weigh glass comminuted to a powder and heated in n-butylamine until complete dissolution. To prevent oxidation, deposition and annealing of the films was carried out in an atmosphere of nitrogen chemically inert. The substrate is placed on a device for rotating, it was applied to the solution and the substrate was rotated at a speed of several thousand revolutions per minute. Annealing of the films was carried out at 100 °C for 1 hour. Measurement of the electrical conductivity of the obtained films was conducted at a constant current and variable depending on the conductivity values ​​in the temperature range from 20 to 100 °C. Measurement of diffusion coefficients was performed according to the absorption method. From diffusion experiments, the values ​​of the diffusion coefficients 110mAg isotope cations in copper chalcogenide films. It was found that the values ​​of the diffusion coefficients of the ions Ag+ in a chemically deposited films and the original glasses are indistinguishable. The analogy of the diffusion coefficient values ​​110mAg isotope in chalcogenide glasses and films based on them can be attributed to the preservation of the polymer network connections chalcogenide glasses when dissolved in organic bases (amines). During application and film formation the polymer (macromolecular) structure of chalcogenide glasses of the solution is maintained.

Characterization and Vertical Elements Distribution of ZnGeP2 Single Crystals

A large, crack-free ZnGeP2 single crystal with size of Φ26 mm×70 mm was grown in a vertical three-zone tubular furnace by modified vertical Bridgman method, i.e. real-time temperature compensation technique with small temperature gradient in double-wall quartz ampoule. The as-grown single crystal was characterized by X-ray diffractometer (XRD), energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It was found that there is a face of (100) and its second-order XRD peaks were observed. The vertical elements distribution of the main part of the grown crystal has a stoichiometric ratio which is close to the ideal stoichiometry of 1:1:2. The IR transmittance of a sample of 2.5 mm thickness is above 58% in the range from 3500 to 800 cm-1. All these results demonstrate that the quality of the ZnGeP2 single crystal grown by the modified method is good, and could be used in the preparation of devices.