Crystallography Reports最新文献

The results of the study of the photoluminescent and X-ray luminescent properties of a p-terphenyl crystalline element made of a single crystal grown from a melt using the Bridgman method are presented. The transmission, photoluminescence, and X-ray luminescence spectra of the crystals were obtained and analyzed. The kinetics of photoluminescence and X-ray luminescence decay have been studied for p-terphenyl single crystal, and the absolute light yield of X-ray luminescence has been determined.

Monoethanolaminium trifluoroacetate (HO‒CH₂CH₂‒NH(_{3}^{ + }) ^‒O(O)C‒CF₃), triethanolaminium trifluoroacetate ((HO‒CH₂CH₂)₃NH^{+ ‒}O(O)C‒CF₃), tris(hydroxymethyl)methanaminium trifluoroacetate ((HO‒CH₂)₃C-NH(_{3}^{ + }) ^‒O(O)C‒CF₃), and 2,2'-(ethylenedioxy)di(ethylaminium) bis(trifluoroacetate) (CF₃-C(O)O^{‒ +}H₃N-(CH₂CH₂O)₂CH₂CH₂-NH(_{3}^{ + }) ^‒O(O)C‒CF₃) were synthesized by the reactions of trifluoroacetic acid with monoethanolamine, triethanolamine, tris(hydroxymethyl)methanamine, and 2,2'-(ethylenedioxy)di(ethylamine), respectively. Ammonium trifluoroacetate (NH(_{4}^{ + }) ^‒OC(O)CF₃) was prepared by the reaction of trifluoroacetic acid with hexamethyldisilazane and with trimethylsilyl trifluoroacetate CF₃C(O)OSi(CH₃)₃. The synthesized compounds are low-melting crystalline salts, which are transferred into a vapor phase upon heating to 200–220°С. The reaction of CF₃C(O)OSi(CH₃)₃ with monoethanolamine afforded monoethanolaminium trifluoroacetate instead of expected 2,2,2-trifluoro-N-(2-hydroxyethyl)acetamide CF₃C(O)-NH-CH₂CH₂OH. The aminium salts were characterized by IR and NMR spectroscopy, mass spectrometry, high-performance liquid chromatography, and scanning electron microscopy. The thermal behavior and thermal stability of the salts were studied by differential scanning calorimetry and thermogravimetry, respectively. The molecular structures of monoethanolaminium trifluoroacetate, triethanolaminium trifluoroacetate, tris(hydroxymethyl)methanaminium trifluoroacetate, and ammonium trifluoroacetate were determined.

The Laakso–Taagepera index belongs to Hill numbers, which characterize diversity of species. The paper demonstrates application of this index for comparing the distributions of structures from the databases ICSD (116 860 records), CSD (1 294 724 records), PDB (184 841 records), and RRUFF (~5.5 thousand mineral species) over space-group types, crystal classes, and crystal systems.

Rb₃CoCl₄NO₃ samples applicable for studying spectral characteristics have been obtained for the first time and investigated in the wavelength range λ = 200–800 nm. Transparency windows are found at the UV–visible and visible–IR boundaries. Differential-scanning calorimetry/thermogravimetry analysis revealed that the Rb₃CoCl₄NO₃ crystal is thermally stable, melts without decomposition, and undergoes two reversible phase transitions. The structure of Rb₃CoCl₄NO₃ single crystals was studied by X-ray diffraction in the temperature range of 293–625 K.

The effect of the bias electric field E₌ (0–10 kV/cm) on the dielectric properties of the VDF₆₀/Tr₄₀ copolymer was studied in the temperature range of 20–110°C. It was found that the dielectric nonlinearity Δε is negative in the polar phase and becomes positive above the Curie temperature (T_C). The increase in T_C under the field E₌ is not uniform. At E₌ < E_c (E_c is the threshold field), the Curie temperature is practically independent of E₌. At E₌ > E_c, an increase in T_C is observed. The presence of the threshold field indicates the existence of sources of random electric fields in the material under study. It is suggested that they are responsible for the smearing of the ferroelectric phase transition.

The results of the experimental study at the KISI-Kurchatov synchrotron source of the new phase-contrast imaging scheme for micro-objects using a nanofocusing compound refractive lens are presented. Visualization with submicron spatial resolution of a Fresnel zone plate with the width of the outer zones less than 0.5 µm is demonstrated. It is found that in the performed experiments the main contribution to the instrumental function, which limits the spatial resolution, is due to the vibrations of the optical scheme elements. The possibility of using the proposed scheme for estimating the beam transverse size at the focus of the compound refractive lens, with allowance for the instrumental function, is demonstrated.

A comparative study of the growth processes, microstructures, and electrical characteristics of oxide/metal/oxide trilayer structures of different compositions synthesized at 50°C by rf magnetron sputtering in argon has been performed. The effect of subsequent annealing in an open atmosphere on the conductivity of the structures has been investigated. Transmission electron microscopy and energy-dispersive X-ray spectroscopy have been used to examine changes in the microstructure and profiles of distribution of chemical elements included in the structures under annealing. Based on the results obtained, mechanisms have been proposed for the transformation of interlayer interfaces and conditions of carrier transport in the structures, depending on the composition of the oxide and metallic layers comprising them.

The new lithium niobate-tantalate hybrid optical material platform can be used for special tasks in integrated photonics: waveguides, periodical poling, modulators and sensors. A comparison of structure and optical characteristics was performed between optical waveguides obtained by annealed proton exchange in lithium niobate (LN) and mixed lithium niobate-tantalate (LNT) solid solutions. The prism coupling method, IR-spectroscopy and X-ray diffraction were used to study the annealed proton exchange waveguides. The calculated increment of refractive index after proton exchange was 0.129 for LNT compared to 0.112 for LN. This unusual high increase of the refractive index of LNT is likely due to the presence of both compressive and tensile deformations of the crystal lattice of LNT as a result of proton exchange. The results of IR-spectroscopy indicate a more intense proton exchange in mixed crystals, which leads to greater structural disorder, in contrast to LN. The diffusion coefficients are higher for LNT unlike LN crystals and annealing relaxation of crystal lattice stresses is faster, subsequently. This is the first report on using proton exchange technology for optical waveguides fabrication in LNT solid solutions.

CaMo(_{{(1-x)}})W_xO₄ solid solutions have been simulated using the interatomic potential method. The dependences of the unit-cell parameters and volume, density, bulk modulus, enthalpy, vibrational entropy, and heat capacity on the composition were determined, and temperature dependences of the heat capacity and vibrational entropy were plotted. The local structure of the solid solutions was investigated. The coordination polyhedra СаО₈, as well as МоО₄ and WO₄ tetrahedra, were found to change with variation in the solid solution concentration. It is shown that all polyhedra are additionally distorted in intermediate compositions, which may be a cause of the improvement of the spectral characteristics of mixed compositions.