Crystallography Reports最新文献

Small-angle scattering (SAS) of X-rays and neutrons is a technique for studying the subatomic structure of condensed matter with a resolution of tenths to hundreds of nanometers, the capabilities of which have grown significantly in recent decades due to the emergence of bright synchrotron radiation sources and laboratory facilities with microfocus sources. The growth of computing power was accompanied by the development of new algorithms and techniques for data analysis, which made SAS one of the most effective methods for studying nanoscale structures. After a brief presentation of the basic principles of SAS for isotropic dispersed nanosystems, some of the most striking examples of such analysis are given: modeling the structure of biological macromolecules in solution, determining the size distributions of inhomogeneities in polydisperse systems, and studying multicomponent systems of nanoparticles of different nature. The SAS method does not require special sample preparation and allows studying objects under conditions close to natural ones, which is especially demanded in the development of nature-like technologies.

The results of studying the crystallization of anthracene, tetracene, and pentacene under conditions of physical vapor transport in growth systems with one- and two-zone thermal fields are presented. Specific features of the phase behavior and thermal stability of compounds have been investigated by differential-scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in order to find the thermal modes of sublimation of materials providing crystal growth without any damage due to chemical degradation. Conditions for growing crystals on the centimeter scale (0.2–2 cm) are determined for growth systems with one- and two-zone thermal fields. A series of field-effect transistors with upper drain/source electrodes and upper gate were fabricated based on grown pentacene crystals, and their electrical characteristics were investigated.

The results of the studies performed at the Shubnikov Institute of Crystallography and devoted to the development of UV optical filters based on complex nickel and cobalt compounds are reviewed. The structural dependence of the optical properties of these crystals and their thermal stability is discussed. The fundamental features of mixed crystals grown from solution and developed approaches to the design of optical filters based on structurally perfect mixed K₂(Co,Ni)(SO₄)₂⋅6H₂O crystals are described. The possibility of designing UV-А optical filters by partial substitution of the ligand environment of transition metal ions is demonstrated.

A brief retrospective of the development of laboratory X-ray microtomography at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences (IC RAS) is given. The main methods and approaches that made it possible to increase the informativeness of microtomography measurements—the use of monochromatic radiation, phase-contrast method, and diffraction tomography (topo-tomography)—are reported. Designs of the instruments developed and currently functioning at the IC RAS are described, and some experimental results obtained on them are presented.

New approaches to the X-ray imaging of joints using different radiation sources are discussed. The structure of a joint cartilage tissue and model objects similar to the cartilage tissue in structure and properties have been studied using X-ray radiation of a laboratory microtomograph and synchrotron radiation. Projection radiography and microtomography images of the internal structure of the model objects and cartilage tissue impregnated with a radiopaque substance have been obtained. Colloidal solutions of titanium and molybdenum oxide bronze biofunctional nanoparticles have been used as contrast agents. The tissue depth distribution of the nanoparticle concentration has been measured by processing the images.

ZnO microcrystal arrays have been grown on a (111) silicon substrate by the vapor‒liquid‒crystal deposition, where the liquid phase is gold. The differences between the crystals obtained for growth times of 5, 10, and 15 min are described. The lattice parameters of the microcrystals have been calculated with increasing growth time: а = 3.316 Å, c = 5.281 Å; а = 3.291 Å, c = 5.270 Å; and а = 3.286 Å, c = 5.258 Å. A change in the Au content in the microcrystals during their growth has been found to vary from 0.520 at % at the substrate to 0.035 at % on the surface of the crystals after the 15-min growth. Elemental distribution maps are presented, and the deviation of the lattice parameters of the obtained crystals from the reference values is explained.

Rare-earth molybdenum-containing oxides of the nominal composition Li_xNd(_{{5-x}})Mo₃O(_{{16, pm ,delta }}) (x = 0, 0.05, 0.15, 0.25) with a fluorite-related structure have been obtained for the first time as single crystals grown from flux and by solid-phase synthesis in air in the form of polycrystalline samples. The new phases are characterized using X-ray diffraction analysis, simultaneous thermal analysis, and impedance spectroscopy. X-ray diffraction analysis showed that lithium atoms are localized near the positions of rare-earth cations. The chemical formula of the investigated single crystal is Li_0.216Nd_4.784Mo₃O(_{{14.1 + delta }}). The low lithium content did not affect significantly the ability of the studied phases to dissociative absorption of water but led to a decrease in the total conductivity of Li_xNd(_{{5-x}})Mo₃O(_{{16, pm ,delta }}) lithium ceramics.

The congruent melting compositions in the MF₂–M'F₂–RF₃ systems (M ≠ M' = Ca, Sr, Cd, Ba, Pb; R are rare-earth elements (REEs)) have been determined based on thermodynamic topological analysis. Crystals of fluorite solid solution in the PbF₂–CdF₂–RF₃ (R = Tb, Ho, Er, Tm, Yb, Lu) systems were grown by the vertical directional crystallization technique. Their phase composition and distribution of components over the crystalline boule length were investigated. Crystals of congruently melting solid solutions (Pb_0.67Cd_0.33)(_{{1-x}})R_xF(_{{2 + x}}) (R = Tb, Ho, Er, Tm, Yb, Lu) were grown for the first time. Traces of low-temperature transformation—a phase isostructural to the Pb₂YF₇ compound (sp. gr. I4/m), in which Y sites are occupied by the corresponding R cations and Pb sites can be partially occupied by Cd cations—were found in the crystals with R = Ho, Er, Tm, and Yb. The crystals with R = Tb and Lu have a high degree of homogeneity and are suitable for optical studies.

CdTe thin films were grown on Si(111) and Al₂O₃(0001) substrates by thermal vapor deposition. The obtained films were studied by atomic-force and scanning electron microscopy, as well as by X-ray diffraction analysis. It was found that thin films of both wurtzite and sphalerite CdTe modifications can be grown on Al₂O₃(0001) substrates. Thin films of the sphalerite CdTe modification can be obtained on Si substrates. It was shown that the elemental composition of thin films is close to stoichiometry, and, in the case of thin films grown on Al₂O₃(0001), the deviation was no more than 1 at %.

The luminescence and scintillation characteristics of cerium-doped yttrium aluminum garnet crystals grown from melts in vacuum have been analyzed. Absorption and X-ray luminescence spectra, X-ray luminescence decay kinetics, and scintillation specific light yield in a wide range of activator concentrations (from 0.0036 to 1.175 at % with respect to substitution for yttrium at the c sites of the garnet structure) have been studied. Effective quenching of the intrinsic luminescence of antisite and vacancy defects of the base crystal in the UV region with an increase in the activator concentration has been found. The optimal activator concentration has been determined in order to increase the X-ray luminescence intensity and the scintillation light yield of Ce³⁺ ions, with allowance for the technological features of growth of single crystals of high optical quality with a high Ce³⁺ concentration by the horizontal directional crystallization in vacuum. The dependences of the X-ray luminescence kinetics on the activator concentration have been analyzed. It is shown that crystals with the specific light yield up to 25 000 ph/MeV can be grown.