Crystallography Reports最新文献

The effectiveness of biotechnological processes depends on the stability of the enzymes used in them, including their temperature stability, stability in high salt concentrations, and stability at extreme pH values. This is especially important for enzymes used in the food, paper, textile, and chemical industries, such as pectinases, cellulases, and alpha-amylases. The most sought-after enzyme in many biotechnological processes is cellulase, which has led to its widespread use and rapid spread on the global market. The structural features of a new thermostable cellulase, Cel7465, isolated from a thermal spring in the Republic of North Ossetia-Alania were investigated. Through comparative analysis of the cel7465 gene sequence against known nucleotide sequence databases, we were able to assign this gene to a non-cultivable microorganism belonging to the Fimbriimonadales order. The system of expression and purification of recombinant Cel7465 protein was optimized. The small-angle X-ray scattering method was used to investigate the structural features of the enzyme.

A model of the bcc → hcp phase transition has been built, in which the {112} crystallographic planes shift in the 〈111〉 and 〈112〉 directions. The shift in the 〈112〉 direction leads to contraction, while the shift in the 〈111〉 direction causes pure shear. Numerical values of the deformation anisotropy during the phase transformation have been obtained. High-temperature X-ray diffraction and dilatometry data have been obtained to estimate the strain during the bcc → hcp phase transition in VT1-0, VT6, and VT41 titanium alloy samples.

A model of magnetohydrodynamic domains is proposed. It describes the motion of a nematic fluid with negative diamagnetic susceptibility in the geometry of transverse bending deformation, when an arbitrary angle is specified between the initial orientation of the director and the magnetic field strength vector. The modeling results are compared with experimental data on the observation of the domain structure in a lyotropic nematic under the above-described condition.

Rocking curve imaging has been used for the first time to plot maps of excess arsenic spatial concentration in the LT-GaAs layer in a GaAs/AlAs/AlGaAs/LT-GaAs(100) heterostructure, grown by molecular-beam epitaxy. An area detector with a matrix size of 14 × 14 mm and a resolution of 55 µm was used to localize regions with different concentrations of excess As atoms: from 0.86 × 10²⁰ to 0.96 × 10²⁰ cm^–3. The concentration of excess arsenic was determined by analyzing the difference in the angular positions of the diffraction peaks from the GaAs substrate and the LT-GaAs layer, which is due to the increase in the unit-cell parameter, caused by incorporation of arsenic atoms into gallium sites (As_Ga).

Needle-like, plate-like, and bulk Cd₃As₂ crystals with record values of weight and sizes have been grown by the chemical transport reaction method using vertical mass transfer. The mass transfer and growth rate were calculated based on the data on the partial vapor pressures of Cd and As₄ in order to optimize the growth conditions. Identification and monitoring of the structural quality of crystals were performed using a complex of methods of physicochemical analysis, including X-ray phase analysis, as well as atomic-force, optical, and electron microscopy.

Crystal growth in a heterohomogeneous chemical system can be described phenomenologically on the basis of the limiting principle of nonequilibrium thermodynamics. However, the existence of two mutually exclusive principles—maximum (Ziegler’s principle) and minimum (Prigogine’s principle) of entropy production density—creates a problem in thermodynamic analysis of real crystallization processes. As a result of experiments, the crystallization conditions for four calcium phosphate phases—monetite, brushite, octacalcium phosphate, and hydroxyapatite—in a closed solution–gel chemical system have been established, and a mathematical model of formation of an amorphous phase of calcium phosphate, serving as a precursor for crystalline phases, has been proposed. Three stages of system development are observed. The thermodynamic systems whose development obeys the Ziegler’s and Prigogine’s principles, are implemented at three characteristic scale levels: for a diffusion column of full volume; for the edge section of the Lisegang strip or the surface of a growing crystal with a boundary zone having a thickness of no more than 0.5 mm; and for the contact region of metastable and stable structural varieties of phosphate crystals up to 10 µm thick. The development times of quasi-closed and open systems range from 1 h to several days.

The factors that may cause the effect (found experimentally previously) of a strong change in the lateral projection of polarization (calculated based on second optical harmonic measurements) in thin polycrystalline spherulitic films of lead zirconate titanate with a change in the geometric sizes of perovskite blocks in the range from 10–15 to 35–40 µm have been considered. It is suggested that these changes are caused by the action of strong lateral stresses, leading to a change in the film microstructure, reorientation of the ferroelectric polarization in the directions maximally close to the substrate plane, and formation of induced polarization. The maximally possible contributions of these stresses to the observed effect, when the film composition is close to the morphotropic phase boundary from the side of the rhombohedral modification of the ferroelectric phase, are estimated.

The paper presents the results of studying the types of dislocation structures in polycrystalline Cu–Al and Cu–Mn alloys with different additives of the second element. The quantitative parameters of these structures were investigated at different degrees of deformation. The transmission electron microscopy (TEM) data are reported. Alloys of homogeneous solid solutions with different solid-solution strengthening were investigated. The role of the average scalar dislocation density is determined. The following parameters of the dislocation substructure were measured: the values of dislocation density in walls and in cells, the sizes of cells, and the width of their walls. The relationship between the dislocation structure parameters and the value of solid-solution strengthening during the accumulation of dislocations in the material after plastic deformation is established.

In mixed crystals (solid solutions) with the fluorite structure ({text{C}}{{{text{a}}}_{{1-x}}}{text{G}}{{{text{d}}}_{x}}{{{text{F}}}_{{2 + x}}}), doped with Ce³⁺ and Pr³⁺ ions, efficient energy transfer from the matrix Gd³⁺ ions to the impurity rare-earth ions has been demonstrated. The process of energy transfer between Gd³⁺ ions and impurity ions was studied to assess the potential of the gadolinium-containing matrix as a sensitizer for Се³⁺ and Pr³⁺ ions in order to create γ-radiation scintillators. The obtained results showed that Gd³⁺ absorbs γ radiation and X-ray photons, increasing the emission of Се³⁺ and Pr³⁺ ions. X-ray luminescence studies with different contents (from 0.3 to 5.0 mol %) of the second matrix component GdF₃ in the mixed crystal and a low concentration (0.3 mol %) of rare-earth impurity ions showed that the resonant cross-relaxation mechanism of donor–acceptor energy transfer turns into migration mechanism (through the gadolinium sublattice to the impurity ion) with an increase in the content of donor ions (Gd³⁺). The obtained amplitude spectra showed an increase in the light yield with increasing the Gd³⁺ content in the scintillator matrix.

Magnetic films for magnetic field concentrators should have high magnetic permeability. Reproducible electrochemical deposition of Co–Ni–Fe films with predominant face-centered cubic lattice and high gain of  the weak magnetic field (related to their high magnetic permeability) was developed using a chloride electrolyte. The magnetic properties and structure of electrochemically deposited Co–Ni–Fe films with varying ratios of Co, Ni, and Fe atomic concentrations have been studied. Using the TREMAG alloy (Co₆₀Ni₂₀Fe₂₀) as an example, it was established that its high permeability in weak magnetic fields is mainly determined by the crystal structure and the chosen stoichiometric composition of the Co–Ni–Fe film.