Crystallography Reports最新文献

The results of computer simulation of the conditions for growing guanylurea hydrophosphite (GUHP) crystals from solution, including the temperature patterns of the outer walls of the thermostat and crystallizer, are reported. Qualitative features of the location of temperature minima and maxima in the volume of the growth unit for different methods of solution mixing in the crystallizer were revealed. The flow patterns in the crystallizer in dependence of the mixing method are shown. Based on the simulation results, the optimal GUHP growth regime was selected and bulk single crystals up to 90 × 35 × 15 mm³ in size were obtained. The features of their real structure have been studied by projection X-ray topography.

Molecular dynamics simulations revealed notable thermal stability of the precursor cluster (the dimer that forms prior to the crystallization) of proteinase K crystals in the temperature range of 20–60°C. The analysis of the intermolecular contact area in the dimer confirmed that its structure is preserved up to 60°C. This finding led to the hypothesis that this thermophilic protein can be crystallized at a temperature corresponding to its maximum catalytic activity (50–60°C). This theoretical prediction was confirmed experimentally: crystals of proteinase K were successfully grown after incubation at 60°C. These results demonstrate the practical value of the molecular dynamics approach as a tool for predicting crystallization conditions and offer prospects for determining the structure of proteinase K in the functionally relevant conformation, which is in line with current trends in structural biology of thermophilic proteins.

The effect of postgrowth annealing on the dislocation structure of low-dislocation-density germanium single crystals 100 mm in diameter, grown by the Czochralski method, has been studied. The annealing was performed under isothermal conditions at 700°C for 40 h in the thermal unit of the growth system after detaching the crystal from the melt, before cooling. It was found that the dislocation density in the crystals subjected to postgrowth annealing ranges from 14 to 105 cm^–2, which is on average five times lower than in the crystals grown under identical conditions but without annealing.

The structure of two-phase whiskers of niobium trisulfides NbS₃ has been studied using various electron microscopy methods. The whisker is a highly textured polycrystal, consisting of two crystalline phases: NbS₃-I and NbS₃-II. Two orientation relationships between the phases were determined using electron diffraction. Pores and dislocations were found at the interphase boundaries, and models of the interphase boundaries were proposed. The structure of stacking faults of various types in the crystalline phase NbS₃-II was revealed.

The results of studying the multilayer mirrors (periodic Ti/Ni structures with different configurations of Si buffer layer), which are promising in developing mirror optics for synchrotron radiation, are presented. Samples with period structures Ti/Ni, Ti/Si/Ni, Ti/Ni/Si, and Ti/Si/Ni/Si were investigated by X-ray reflectometry and X-ray standing wave (XSW) methods. It is found that the Ti/Ni system is characterized by the largest thicknesses of transition layers at the Ti/Ni interfaces. Addition of Si interlayers between Ti and Ni layers leads to a decrease in the transition layer thicknesses, while addition of Si only within a period or only between periods leads to asymmetry of electron density profiles and elemental distribution profiles over the structure depth. It is shown that the structure with a Si buffer layer both between layers within a period and between the periods themselves (Ti/Si/Ni/Si) is an optimal mirror configuration in terms of reflectometry intensity.

The temperature dependence of solubility in the NiCl₂–H₂O system in the temperature range of 25–60°C has been studied. The temperature ranges of crystallization of NiCl₂⋅6H₂O and NiCl₂⋅4H₂O compounds have been determined. Single crystals of nickel chloride hexahydrate and tetrahydrate have been obtained, the size and quality of which allowed to estimate the equilibrium faceting and optical spectra. A comparative analysis of the thermal stability of the obtained crystal hydrates was carried out. It was found that the transparency band in the short-wavelength range for nickel chloride crystals is shifted to the long-wavelength range as compared to the nickel sulfate crystal.

The results of structural studies using X-ray and electron microscopy diagnostics of NiO films obtained by magnetron sputtering have been analyzed. The difference in the phase and structural composition of films of different thicknesses before and after annealing is shown. The reasons for these differences are discussed, as well as the role of the interface layer formation for obtaining stable nanoscale NiO films on sapphire substrates.

The possibilities of growing ultimate sulfide crystals from a sulfuric melt in a stationary temperature gradient are described. The optimum synthesis mode is achieved when the temperature of the hot end (charge) is 550°C and the temperature of the cold end (crystallization region) is 460°C. As a result, TiS₃, ZrS₃, HfS₃, V₄₀S₆₀, NbS₃, TaS₃, PdS₂, CuS, Ag₂S, metallic Au, HgS, CdS, Ga₂S₃, In₂S₃, SiS₂, SnS₂, PbS, Sb₂S₃, and Bi₂S₃ crystals of millimeter and submillimeter sizes were grown. Only polycrystalline agglomerates several tens of micrometers in size were obtained when transferring some metals, in particular, tungsten. The possibility of growing crystals of double sulfides was demonstrated using CrPS₃ as an example. The considered technique makes it possible to obtain crystals of the required quality without special equipment; the small size of crystals is sufficient for laboratory study.

Problems in experimental study of real crystal structures using phase-contrast imaging with synchrotron radiation (SR) are discussed, and methods for their solution are proposed. The experiment was performed at the Pohang Light Source in Pohang City, Republic of Korea. Diamond crystals were examined. The capabilities of the method in studying weak changes in the crystal density under conditions of spatially inhomogeneous beam intensity, beam statistical noise, and detector imperfections were analyzed. Images of various shapes and sizes were obtained, which indicated the presence of defects. However, a more detailed analysis is required to identify these defects.

An approach proposed in this study, which is based on the hydrogen permeation method, has been used to determine the temperature dependence of the terminal solid solubility of hydrogen in iodide-refined hafnium GFI-1 in the temperature range from 350 to 550°C. The experiments were performed in the regime with maintaining a low constant saturation rate for a membrane sample, instead of the traditionally used regime with maintaining constant input pressure. This approach made it possible to obtain the values of terminal solid solubility under the conditions maximally close to equilibrium. It is shown that the obtained results are in good agreement with the few available data in the literature for the same temperature range.