Volume 69, Nº 4 (2024)

The features of focusing X rays using a refractive-diffractive lens (RDL), which is a system of two asymmetrically reflecting crystals with asymmetry factors, the product of which 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 is 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.

Impurity defects simulation in sodium-gadolinium molybdate NaGd(MoO₄)₂ was carried out using a method of interatomic potentials. The dissolution energies of tri-, di- and monovalent impurities were estimated. The dependences of the dissolution energy on the ionic radius of the impurity were plotted. For heterovalent substitutions, the most energetically favorable mechanism for charge compensation has been found, both due to intrinsic crystal defects and according to the conjugate isomorphism scheme. The positions of the most probable localization of defects are determined. The effect of disordering of sodium and gadolinium ions at equivalent positions on positional differences in the energy of defects is estimated. A comparison of the solubility of impurities in NaGd(MoO₄)₂ and its isostructural CaMoO₄ indicates that, although isovalent substitutions are energetically more favorable than heterovalent ones, the mechanism of conjugate isomorphism, which ensures electrical neutrality, can equalize these processes.

A number of new isostructural ternary intermetallides of the composition R₄Ru₂Ga₃ (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) have been discovered in R–Ru–Ga ternary systems. X-ray examination of the Nd₄Ru₂Ga₃ single crystal showed that this compound crystallizes in the monoclinic system and is a representative of a new structural type: a = 10.899(3), b = 4.0533(11), c = 9.720(3) Å, β = 111.080(7)°, C2, Z = 2, R1 = 0.043, wR2 = 0.077 for 1518 reflections. A feature of the structure is the presence of distorted fragments of RuNd₆ (type AlB₂) and GaNd₈ (type CsCl) in it. The minimum Nd–Ru distance in a polyhedron is 2.8463(16) Å, which is significantly shorter than the sum of their atomic radii. The parameters and volumes of the elementary cells in the R₄Ru₂Ga₃ series (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) decrease in accordance with lanthanide compression, and the melting temperatures increase.

The synthesis of 1,4-di(bromomethyl)-2,5-diiodo-benzene (1), diacetate of 2,5-diiodo^–1,4-di(hydroxymethyl)benzene (2) and diiodide of 1,1’-[(2,5-diiodo-1,4-phenylene)bis(methylene)]dipyridinium (3) is described and their crystallographic data are given. All three crystal structures are characterized by the stacked packing of planar molecules and the presence of halogen bonds I–Br, I–O, and I–I, respectively. The number of halogen bonds is maximum in compound 1: two I–Br bonds for each halogen atom. Compounds 2 and 3 contain one halogen bond per halogen atom, but they are significantly shorter than in compound 1. All crystals were investigated by IR spectroscopy and synchronized thermal analysis. Compound 1, which has no ionic or hydrogen bonds, melts at a higher temperature than ionic compound 3 (218 and 200°C, respectively) due to the presence of a large number of intermolecular halogen bonds. Compound 2 melts at a lower temperature (151°C), which is characteristic of esters.

A technique for arbitrary symmetry crystals unit cell parameters refining on modern single-crystal diffractometers is described. The technique is based on the 2D detector position calibration. The elementary orthorhombic unit cell parameters of the α-³³S single crystal have been refined. The anisotropy of parameters changes in the range of 90–350 K has been studied. It is shown that the relative increase in parameter c is 6.4%. The obtained dependences are approximated by second–third degree polynomials. The absolute increase in cell volume is 138.4 A3, and the relative increase is 4.3%. The temperature dependencies of the thermal expansion tensor elements has been refined. The coefficients of α-³³S thermal expansion tensor at the room temperature are: α₁₁ = 15.35 × 10^–5, α₂₂ = 8.56 × 10^–5, α₃₃ = 9.12 × 10^–5 К^–1.

Ice brittleness and low strength limits its usage as a construction material in cold climate regions on Earth (Arctics, Antarctic, high mountain regions on other continents) as well as in construction of habitable colonies at Moon and Mars planned by several countries despite attractiveness of its other properties. The paper presents experimental study of enhancement of ice carrying capacity and fracture energy by introduction of SiO₂ nanoparticles and polyvinyl alcohol into it. Concentration dependences of these properties enhancement are found. Quantitative characteristics of transition from brittle fracture mode in pure ice to ductile one in ice composite caused by growing content of additives are revealed. This transition results in 2–3 orders of magnitude increase in ice fracture energy.

The structure of epitaxial films of the GaInP solid solution, in which ordering occurs, was studied using transmission electron microscopy. The films were grown by metalorganic vapor phase epitaxy on GaAs (001) substrates near the half-composition point. During the study, dark-field images obtained using superstructure reflections for cross-sectional and plan-view specimens of films were 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 was discovered, while in the bulk of the film the domains are uniformly located and mutually overlap each other. The effect of spatial separation of domains is associated with the lattice relaxation, leading to a change in the surface topology.

The possibility of forming a conductive metal-polymer composite based on an array of intersecting silver-containing nanowires has been demonstrated. It has been determined that the electrical and mechanical characteristics of the composites depend both on the deposition time and on the ratio of the anode to cathode areas. The resulting metal-polymer composites had mechanical characteristics exceeding those of polymer track membranes made of polyethylene terephthalate. At the same time, with an increase in the ratio of anode to cathode areas and an increase in deposition time, the samples exhibit a decrease in the values of electrical conductivity (0.0025 Ω-1 – at 100 growth cycles, 0.0033 Ω-1 – at 50 cycles), strength (90 MPa – at 100 cycles, 99 MPa – at 50 cycles) and elastic modulus (4.7 GPa – at 100 cycles, 5.4 GPa – at 50 cycles). The data obtained indicate that conductive silver-containing nanowires can be reinforcing structures for conductive metal-polymer composites with high electrical conductivity values, promising for use in flexible electronics elements.

Solid electrolyte nanoceramics Pr_1–ySr_yF_3–y (y = 0.03, sp. gr. P3c1) were obtained by high-energy grinding 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 significantly lower than the conductivity of the original single crystal (σ_crys = 4.0 × 10^–4 S/cm), which is due to its low (about ~74% of the theoretical value) density. Heat treatment of nanoceramics at 823 K in vacuum leads to a 3-fold increase in the value of 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 process of collective recrystallization and significant increase the density of ceramics up to 90%. The mechanical grinding technique and subsequent heat treatment of Pr_1–ySr_yF_3–y nanopowder makes it possible to processing 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 direction for further developments in the field of creating fluorine-ion current sources and fluorine gas sensors.

We used the molecular dynamics method to assess the stability of the precursor-cluster (hexamer) of thermolysin crystal over a wide range of temperatures (10–90°C). The simulation results showed that as the temperature increases, the stability of the hexamer, in general, decreases, however, the hexamer does not dissociate at any of the considered temperatures. At a temperature of 60°C, an increase in the stability of the hexamer was observed. This value is close to the temperature of maximum enzymatic activity of thermolysin (70°C). Based on the analysis of the results, it was assumed that the crystallization of thermolysin could be carried out at 60°C.

The close intertwining of equilibrium and nonequilibrium thermodynamic representations and transitions between the two limiting principles of thermodynamics: the second beginning and the principle of least coercion (minimum entropy production in the stationary regime) constitute the main content of phenomenological theories of crystal growth. The difference of basic postulates of two sections of thermodynamics forces to discuss problems of reversibility and irreversibility of time, scales of observed phenomena and rules of conjugation of thermodynamic forces and flows in theories of crystal growth. A variant of the solution of some conjugation problems is shown on the example of the fluctuation model of dislocation crystal growth, which is based on the stationary isothermal process of thermodynamic free energy fluctuations. In the case of the limiting mode of adsorption of impurities on the crystal face according to the Langmuir model, the free energy fluctuations possessing the absence of the memory effect allow us to identify three chemical potentials of building particles that determine the corresponding values of solution supersaturations realized at different scale levels at the growing crystal face containing a helical dislocation. The supersaturations control quasi-equilibrium and nonequilibrium thermodynamic processes that constitute a single dislocation mechanism of crystal growth.

A tool for X-ray hyperspectral imaging has been developed. It is based on a conventional CCD driven by an algorithm that allows resolution in both energy and position. A new algorithm has been developed that allows the real-time analysis of single photon events. The factors influencing the energy resolution, the formation of artifacts in the energy spectra, and the counting efficiency are analyzed. Furthermore, a method for achieving sub-pixel precision using the singular value decomposition is suggested. The algorithm has been tested on synthetic data and in a live experiment with the registration of X-ray fluorescence emission from a thin film structure. Applying hyperspectral imaging to grazing emission X-ray fluorescence opens up new possibilities in nanometrology.