Crystallography Reports最新文献

A technique for refining unit cell parameters of crystals belonging to arbitrary systems 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 change in the parameters in the range of 90–350 K has been analyzed. The relative increase in the parameter c is shown to be 6.4%. The obtained dependences are approximated by second–third degree polynomials. The absolute and relative increments in the unit cell volume were found to be 138.4 ų and 4.3%, respectively. The temperature dependences of the thermal-expansion tensor elements have been refined. The coefficients of thermal expansion of α-³³S at room temperature turned out to be α₁₁ = 15.35 × 10^–5, α₂₂ = 8.56 × 10^–5, and α₃₃ = 9.12 × 10^–5 K^–1.

The low strength and high brittleness of ice, with all attractiveness of its other properties, limit its wide application as a construction material in cold climate regions on the Earth (Arctic, Antarctic, and high-altitude regions on all continents) as well as in construction of habitable colonies on the Moon and Mars, planned by several countries. We experimentally investigated the possibility of increasing the bearing capacity and fracture energy of ice and nanocomposites on its basis by introduction of polyvinyl alcohol and SiO₂ nanoparticles into their composition. The concentration dependences of the effects improving these mechanical characteristics have been studied. The fundamental possibility and quantitative laws of the transition from the brittle fracture mode in pure ice to the ductile mode with an increase in the content of additives in ice composites and, as a consequence, dramatic (by two to three orders of magnitude) increase in their fracture energy have been established.

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 on both the deposition time and the anode-to-cathode area ratio. The mechanical characteristics of the synthesized metal‒polymer composites are better than those of polyethylene terephthalate polymer track membranes. With an increase in the anode-to-cathode area ratio and deposition time, one can observe a decrease in the electrical conductivity (0.0025 Ω^‒1 at 100 growth cycles and 0.0033 Ω^‒1 at 50 cycles), strength (90 MPa at 100 cycles and 99 MPa at 50 cycles), and modulus of elasticity (4.7 GPa at 100 cycles and 5.4 GPa at 50 cycles). Conductive silver-containing nanowires can be used as reinforcing structures of metal‒polymer composites with the high electrical conductivity, promising for use in flexible electronics elements.

The close intertwining of equilibrium and nonequilibrium thermodynamic representations and transitions between 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 the phenomenological theories of crystal growth. The difference of the basic postulates of two sections of thermodynamics forces to discuss the 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 characterized by the absence of the memory effect make it possible to identify three chemical potentials of building particles, which determine the corresponding values of solution supersaturations realized at different scale levels at the growing crystal face containing a screw dislocation. The supersaturations control quasi-equilibrium and nonequilibrium thermodynamic processes that constitute a unified dislocation mechanism of crystal growth.

In the kinematical approximation, a method for rapid numerical calculation of X-ray diffraction from thin crystalline microsystems has been developed. The speed of calculating of reciprocal space maps using this approach is three to four orders of magnitude higher than calculations based on the Takagi–Taupin equations or two-dimensional recurrence relations. Within the framework of the obtained solutions, numerical simulation of X-ray reciprocal space mapping was performed for three models of crystal chips of microsystems.

Glycoside hydrolases catalyze the hydrolysis of glycosidic bonds in diverse substrates. Oral bacteria can metabolize glycosidic precursors present in foods into aroma compounds. This metabolism has an impact on food sensory perception and presumably involves specific glycosidases belonging the glycoside hydrolases. Comprehensive elucidation of the structural and functional characteristics of glycoside hydrolases in oral bacteria is needed for advancing our understanding of aroma compound metabolism within the oral cavity. In this context, we have identified a glycoside hydrolase coded in the Prevotella sp. genome, exhibiting homology to β-glycosidases of the GH1 family. This enzyme, designated as PsBG1, was successfully expressed and purified for crystallographic investigation. PsBG1 crystals belong to the monoclinic space group P2₁ with unit cell parameters a = 134.2, b = 139.5, c = 172.7 Å and β = 99.8°. The crystal structure of PsBG1 was elucidated using molecular replacement techniques, utilizing a predictive model constructed with AlphaFold2. Analysis revealed that the asymmetric unit comprises three copies of homotetramer, while the predominant oligomeric state in solution is also a homotetramer. Ongoing efforts are focused on the refinement and detailed examination of the PsBG1 structure to clarify its functional significance in the metabolism of aromatic compounds.

A position-sensitive spectrometer with subpixel spatial resolution on the basis of a CCD camera has been implemented. The spectrometer operation is based on the proposed algorithm for real-time analysis of frames with single photon-induced events. The factors affecting the energy resolution, formation of artifacts in energy spectra, and count efficiency are analyzed. An algorithm for obtaining subpixel resolution with application of singular value decomposition is proposed. The algorithm operation has been tested on synthesized experimental data and in a live experiment with registration of the spatial and energy structure of X-ray fluorescence emission from a layered system. The application potential of hyperspectral imaging for the experimental method of X-ray standing waves in the geometry of normal incidence and grazing X-ray fluorescence emission is demonstrated.

Impurity defects in sodium–gadolinium molybdate NaGd(MoO₄)₂ have been investigated by the method of interatomic potentials. The solution energies of tri-, di-, and monovalent impurities are estimated. The dependences of the solution energy on the impurity ionic radius are plotted. For heterovalent substitutions, the most energetically favorable mechanism of charge compensation is found, both due to intrinsic crystal defects and according to the conjugate isomorphism scheme. The positions of the most likely localization of defects are determined. The influence of the disordering of sodium and gadolinium ions on the positional differences in the energy of defects is estimated. A comparison of the solubility of impurities in NaGd(MoO₄)₂ and CaMoO₄ (a compound isostructural to it) indicates that, although isovalent substitutions are energetically more favorable than heterovalent ones, the mechanism of conjugate isomorphism (providings electrical neutrality) can equalize these processes.

A number of new isostructural ternary intermetallic compounds of the composition R₄Ru₂Ga₃ (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) were found in ternary R–Ru–Ga systems. The single-crystal X-ray diffraction study of Nd₄Ru₂Ga₃ showed that this compound crystallizes in the monoclinic system and it is a representative of a new structure type (a = 10 Å, b = 4.0533(11) Å, c = 9.720(3) Å, β = 111.080(7)°, space group С2, Z = 2, R1 = 0.043, wR2 = 0.077 for 1518 reflections). The specific structural feature of this compound is the presence of distorted RuNd₆ (AlB₂ type) and GaNd₈ (CsCl type) units. The shortest Nd–Ru distance in the polyhedron is 2.8463(16) Å, which is significantly smaller than the sum of the corresponding atomic radii. The unit cell parameters and volumes in the R₄Ru₂Ga₃ series (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) decrease in accordance with lanthanide compression, while their melting points increase.

The results of studying the electronic states of the conduction band of ultrathin films of furan-phenylene co-oligomer 1,4-bis(5-phenylfuran-2-yl)benzene and the results of analyzing the interfacial potential barrier upon the formation of these films on the surfaces of (SiO₂)n-Si and layer-by-layer deposited ZnO are presented. The formation of a (8–10)-nm-thick co-oligomer film was investigated by total current spectroscopy; the energy range from 5 to 20 eV above E_F was analyzed. Furan-phenylene co-oligomer films on the (SiO₂)n-Si surface have a domain structure with a characteristic domain size of ~1 × 1 µm and surface roughness within a domain of no more than 1 nm. The films on the ZnO surface have a granular structure with a grain height of 40–50 nm.