Crystallography Reports最新文献

The structure of epitaxial films of the GaInP solid solution, in which ordering occurs, has been studied by transmission electron microscopy. The films have been grown by metalorganic vapor-phase epitaxy on GaAs(001) substrates near the half-composition point. The dark-field images obtained using superstructure reflections for cross-sectional and plane-view samples of films have been analyzed. The morphology and relative spatial arrangement of ordered domains have been determined. The phenomenon of spontaneous self-organization of regions with CuPt–B⁺ and CuPt–B^– ordering near the surface has been discovered, while in the bulk of the film, the domains are uniformly distributed and overlap. The effect of spatial separation of domains is attributed to the misfit stress relaxation in the growing epitaxial layer, which changes the surface topology.

The stability of the precursor cluster (hexamer) of the thermolysin crystal over a wide temperature range (10–90°C) has been estimated by the molecular dynamics method. The simulation results showed that, with an increase in temperature, the stability of the hexamer generally decreases; however, the hexamer does not dissociate at any of the investigated temperatures. At a temperature of 60°C, an increase in the hexamer stability has been observed. This temperature is close to the temperature of maximum enzymatic activity of thermolysin (70°C). It is suggested, based on the analysis of the results, that the crystallization of thermolysin can be carried out at 60°C.

1,4-Di(bromomethyl)-2,5-diiodobenzene (1), 2,5-diiodo-1,4-di(hydroxymethyl)benzene diacetate (2), and 1,1'-[(2,5-diiodo-1,4-phenylene)bis(methylene)]dipyridinium diiodide (3) were synthesized, and their crystallographic data are reported. All three crystal structures are characterized by the stacked packing of the planar molecules and the presence of halogen bonds I⋅⋅⋅Br, I⋅⋅⋅O, and I⋅⋅⋅I, respectively. The largest number of halogen bonds was found in compound 1, in which there are two I⋅⋅⋅Br bonds per halogen atom. Compounds 2 and 3 contain one halogen bond per halogen atom; however, these bonds are significantly shorter than those in compound 1. All crystals were studied by IR spectroscopy and simultaneous thermal analysis. Compound 1, which has no ionic or hydrogen bonds, melts at a higher temperature compared to ionic compound 3 (218 and 200°С, respectively) due to the presence of a larger number of intermolecular halogen bonds. Compound 2 melts at a lower temperature (151°С), which is characteristic of esters.

The development of advanced methods for the synthesis of nano- and microparticles for biomedical applications is of considerable interest. A method for synthesizing submicron silver-shelled calcium carbonate particles using a microfluidic chip designed to control the particle formation is proposed. Precise control of reaction parameters enables controlled formation of silver shell and calcium carbonate particles. The distribution of pores in the hybrid particles was analyzed using small-angle X-ray scattering, which gained insight into the complex structure of the pores. The results provide information on the particle morphology and may facilitate the development of new calcium carbonate-based materials for various applications.

The results of the preparation and ground testing of the space experiment for growing Ge(Ga) crystals, planned on board the multifunctional laboratory module as a part of the ISS RS are reported. Under the conditions simulating microgravity, the features of the formation of concentration inhomogeneity in the form of striations when growing crystals under various thermal conditions (in the presence or absence of a free melt surface (Marangoni convection)), as well as when changing technological parameters (variations in growth rate) are investigated. Based on the obtained results of metallographic and electrophysical studies, conclusions are drawn on the peculiarities of the influence of the technological parameters of the crystallization process on the structural perfection of crystals grown under microgravity conditions.

Solid electrolyte nanoceramics Pr(_{{1-y}})Sr_yF(_{{3-y}}) (y = 0.03, sp. gr. (Pbar {3}c1)) were obtained by high-energy milling of melt-grown crystals, followed by cold pressing. The phase composition, microstructure, morphology, and electrical properties of nanoceramics were studied using X-ray diffraction analysis, electron microscopy, and impedance spectroscopy. The room-temperature conductivity of the synthesized Pr_0.97Sr_0.03F_2.97 nanoceramics (σ_cer = 1.7 × 10⁻⁷ S/cm) is much lower than the conductivity of the original single crystal (σ_crys = 4.0 × 10⁻⁴ S/cm), which is due to its low (~75% of the theoretical value) density. Heat treatment of nanoceramics at 823 K in vacuum leads to a threefold increase in σ_cer, and annealing at 1273 K in a fluorinating atmosphere results in further increase in conductivity (σ_cer = 4.3 × 10⁻⁵ S/cm) due to the collective recrystallization and significant increase in the ceramics density (up to 90%). The mechanical milling and subsequent heat treatment of Pr(_{{1-y}})Sr_yF(_{{3-y}}) nanopowder make it possible to process single-phase highly conductive ceramics. The proposed method for the synthesis of ceramic fluoride nanomaterials as a technological form of solid electrolytes is a promising way for further developments in the field of creating fluorine-ion current sources and fluorine gas sensors.

The existence of cavitation zones on the faces of a growing lactose crystal and the driving role of cavitation in the crystal growth have been substantiated. It is shown that the most favorable conditions for the conversion of dissolved lactose into the crystalline state are formed around crystal edges in the phase transition zones. The size of the phase transition zone of the crystallizing substance is calculated and compared with the available data on the sizes of crystalline nuclei. The radii of the cavitation zones were found to be r₂ ~ 7 nm (for a crystal with a size of 60.5 µm, at a temperature of 30°C and supersaturation of 0.55) and r₂ ~ 30 nm (for a 84-µm crystal, at a temperature of 50°C and supersaturation of 1.88). A mathematical model of the growth rate of lactose crystal in a supersaturated solution is proposed. The possibility of studying the crystallization mechanisms and determining the growth rate of lactose crystals based on the theory of dynamic interaction bodies and liquids by A.Y. Milovich is substantiated.

The features of focusing X rays using a refractive–diffractive lens (RDL), which is a system of two asymmetrically reflecting crystals with asymmetry factors whose product is equal to unity, and a refractive lens with a large focal length, are theoretically studied. Crystals make it possible to shorten the focal length of the lens by b² times, where b is the asymmetry factor of the second crystal. A detailed numerical simulation of the effect of radiation focusing using the RDL has been performed. The universal computer program XRWP was used, which was created to calculate the effects of coherent X-ray optics. Analytical formulas are obtained for the optimal aperture and radius of curvature of the lens, as well as for the width of the radiation spectrum that can be focused.

The conditions and specific features of the formation of Langmuir monolayers of symmetric and asymmetric diacetylene N-arylcarbamates and the structural organization of Langmuir–Schaefer films based on them have been studied. The photopolymerization of monolayer solid films of two types of molecules was monitored using absorption spectroscopy; it demonstrated the transition of diyne molecules to the state of blue-phase polydiacetylenes. The efficiency of solid-phase topochemical polymerization reaction in a film of symmetric diynes turned out to be five times higher than in the film of asymmetric diyne molecules. The monolayer surface morphology before and after UV irradiation was studied by scanning electron microscopy.