Crystallography Reports最新文献

The unified model of the cluster structure of nanostructured fluorite crystals in the temperature–composition (T–x) system, proposed by the authors, was used to clarify the evolution of the cluster structure of crystals of the homologous series ({text{C}}{{{text{a}}}_{{1-x}}}{{R}_{x}}{{{text{F}}}_{{2 + x}}}) (R = La–Lu, Y). The defect structures of Ca_0.75Nd_0.25F_2.25, Ca_0.80Tb_0.20F_2.20, and Ca_0.75Y_0.25F_2.25 were studied by X-ray diffraction analysis at 293 and 85 K. They are based on octa-cubic clusters with cuboctahedron cores {F₁₂}. The cores are formed by interstitial anions at the positions 32f (f-type clusters in Ca_0.75Nd_0.25F_2.25 and Ca_0.80Tb_0.20F_2.20) and 48i (i-type clusters in Ca_0.75Y_0.25F_2.25). Obtaining diffraction data with a resolution of 0.29 Å made it possible to identify cation displacements at the positions 24e and 32f in Ca_0.75Y_0.25F_2.25 and clarify the occupancies of these positions. Lowering the temperature from 293 to 85 K does not change the cluster structure of Ca_0.75Nd_0.25F_2.25, Ca_0.80Tb_0.20F_2.20, and Ca_0.75Y_0.25F_2.25. An electron diffraction study of the Ca_0.75Nd_0.25F_2.25 crystal revealed (for the first time) diffuse scattering from structural defects with sizes on the order of one unit cell in crystals of the homologous series ({text{C}}{{{text{a}}}_{{1-x}}}{{R}_{x}}{{{text{F}}}_{{2 + x}}}).

The relationship between the lattice parameters a and the ionic radii r_R of cations in the homologous series of rare-earth oxofluorides with the general formula ROF (12R = La−Er, Y) and the fluorite structure (sp. gr. (Fmbar {3}m)) was investigated. It was found that all ROF compounds obey the following equation: a [Å] = 2.365r_R + 3.004. The special electronic structure of the Y³⁺ cation does not lead to deviation from the correlation equation. The obtained equation makes it possible to determine (from the structural data for fluorite oxofluorides AnOF (An = Ac, Pu, Cm, Cf)) the unknown ionic radii of triply charged actinium cations Ac³⁺ (r_Ac = 1.24 Å) and actinides Pu³⁺ (r_Pu = 1.14 Å), Cm³⁺ (r_Cm = 1.10 Å), and Cf³⁺ (r_Cf = 1.08 Å) for the coordination number 8. Within the framework of the crystal chemical model, the values of the “effective” radii of the fluorine ion (r_F = 1.249 ± 0.017), oxygen ion (r_O = 1.373 ± 0.005), and the average radius of the anion (r_O,F = 1.327 ± 0.009 Å) for fluoride, oxide, and oxofluoride compounds with the fluorite structure were refined. The values of r_F, r_O, and r_O,F can be used in calculations of the crystallochemical properties of fluorite oxofluoride solid solutions.

The paper presents the results of studying the thermal expansion of alloys of the multicomponent system (Tb(_{{1-x}})Y_х)_0.8Sm_0.2Fe₂ (where х is the substitution parameter) using tensometric and X-ray diffraction methods in a wide temperature range. A detailed study of the diffraction pattern was carried out at room temperature; splitting of the peaks was found for compositions with х = 0–0.4, indicating distortion of the initial cubic crystal lattice. Temperature dependences of the thermal expansion coefficient α(T) were plotted and analyzed. Features of thermal expansion in the region of magneto-phase transitions were discussed. A magnetostructural phase diagram of the alloy system (Tb(_{{1-x}})Y_х)_0.8Sm_0.2Fe₂ was constructed.

The crystal structure of a high-calcium eudialyte-group mineral from alkaline rocks of the Khibiny massif has been studied. The trigonal unit cell parameters are a = 14.221(1) Å, c = 30.04(1) Å, V = 5261.3(4) Å³, sp. gr. R3m. The crystal structure has been refined to a final R = 2.8% in the isotropic approximation of atomic displacement parameters, using 1714 reflections with F > 3σ(F). The studied mineral is similar in chemical composition to feklichevite, but differs from it in the predominance of divalent iron, as well as in a lower calcium content and a higher manganese content. The structural features of calcium-rich eudialyte-group members from three alkaline massifs are discussed.

The microhardness of the (100), (001), and (111) planes and the cleavage plane (010) of the GUHP crystal has been studied. It is found that (001) is also a cleavage plane.

Using the method of small-angle X-ray scattering (SAXS), the temperature dependences (in the range from 4 to 30°C with a step of 1°C) of the lysozyme solution structural organization during the growth of tetragonal crystals were obtained for H₂O and D₂O solvents. It was found that, regardless of the solvent type, dimers and octamers are formed in the lysozyme crystallization solution. The volume fractions of the oligomers (dimers and octamers) are inversely proportional to a change in temperature, for both H₂O and D₂O solvents. Under identical temperature conditions, the volume fraction of oligomers in the lysozyme crystallization solution in D₂O is approximately 8% higher than in H₂O. However, the same oligomer content in the lysozyme crystallization solutions in H₂O and D₂O is achieved when the temperature of the H₂O solution is approximately 10°C lower than that of the D₂O solution. This can be explained by the distinct influence of the solvent on protein hydration.

The rapid growth of triglycine sulfate (TGS) single crystals in the ferroelectric phase has been studied. The change in the structural imperfection and crystal habit as a function of supersaturation is demonstrated. The kinetic features of the polar face {010} growth are investigated. It is found that the kinetic curves depend on the effective supersaturation, which leads to nonzero crystal growth rates at zero supersaturation. It is also shown that, at a supersaturation σ < 7%, there is an anisotropy of the growth rates of the (010) and (0(bar {1})0) faces, which disappears at large supersaturations. The reasons for this behavior of the polar facet growth kinetics are discussed.

The interrelation of photoluminescent and piezocatalytic properties of ZnO is studied using as an example an array of tetrapods subjected to mechanical stretching and an array of tetrapods in an organic contaminant solution during ultrasonic treatment. The effect of tensile stresses on the luminescent properties is demonstrated: with a 4% elongation, the integral intensity of the ultraviolet photoluminescence band in ZnO tetrapods decreases by 25%, and its maximum is red-shifted by 1.27 nm. It has been shown that application of ultrasound with a frequency of 40 kHz and power of 120 W increases the efficiency of catalysis using ZnO tetrapods by 42%. The reason for the observed effects is the mechanically enhanced charge separation by piezoelectric fields. The mechanism of acceleration of catalysis under ultrasonic action is discussed.

The effect of long-term exposure of solutions on the growth characteristics of anthracene crystals has been studied. It is established that long-term (>3 weeks) exposure of saturated solutions in air causes their aging with subsequent precipitation of accompanying yellow needle-shaped crystals, along with anthracene crystals. Using single-crystal X-ray diffraction, it was found that the accompanying needle-shaped crystals have a structure described by the sp. gr. P2₁/c (Z = 4) and consist of 9,10-anthraquinone molecules. The formation of solid solutions based on anthracene and 9,10-anthraquinone molecules during their joint crystallization was not revealed. It is shown that the observed red shift of the fluorescence spectrum of crystals, which occurs when using some commercially available grades of anthracene for growth from a solution, is due to the presence of a homologous impurity (tetracene) in the starting material. The crystal-chemical aspects of incorporation of impurity molecules into the anthracene crystal structure are discussed.

The rational design of vaccines requires not only the prediction of immunogenic epitopes but also the thorough evaluation of the structural stability of candidates and their ability to efficiently interact with innate immunity receptors. The stability of four vaccine candidates and their complexes with Toll-like receptors was evaluated by molecular dynamics simulations using the Gromacs-2023 program package. The structures of complexes of the chimeric protein candidates for a vaccine against dengue virus with extracellular domains (ectodomains) of the human Toll-like receptors TLR4 and TLR8 were determined by molecular docking simulations using the ZDOCK server. The affinity of the complexes was assessed with the PRODIGY server.