L. A. Aleshina

Rietveld analysis of X-ray diffraction pattern from β-Ta2O5 oxide

The structure of low-temperature β-Ta2O5 oxide has been studied by the method of Rietveld full-profile analysis. It is established that this oxide has an orthorhombic structure with lattice parameters a = 6.217 Å, b=3.677 Å, and c = 7.794 Å. The atomic coordinates and thermal parameters are also determined.

Change in the hybridization of the N→O group oxygen atom upon complex formation of pyridine and quinoline N -oxides with v-acceptors

It was shown on the basis of X-ray structural and NMR data that the (sp2→sp3) rehybridization of the oxygen atom of the N→O group can take place in reactions of heteroaromatic N-oxides with Lewis and Bronsted-Lowry acids. The hybridization type depends on the ligand and acceptor natures, composition of a complex, and spatial stresses arising during the complex formation.

Analysis of diffuse background on the X-ray diffraction pattern of fullerite C60

Diffuse scattering on the X-ray diffraction pattern of fullerite C60 is analyzed. The characteristics of the short-range order of the amorphous component of fullerite are determined by the Finbak-Warren method. It is established that the short-range order of the amorphous component is similar to the short-range order of lonsdaleite.

Structure and optical properties of LiNbO3:ZnO (3.43–5.84 mol %) crystals

LiNbO3:ZnO (3.43–5.84 mol %) crystals have been studied using Raman spectroscopy and fullprofile analysis of X-ray diffraction data. The results demonstrate that, at ZnO concentrations above 3.95 mol %, their structure is free of NbLi basic defects, which are characteristic of congruent lithium niobate crystals. Increasing the Zn concentration leads to changes in the arrangement of structural units in the cation sublattice along the polar axis and distorts the BO6 (B = Nb, Li, Zn, or a vacancy) oxygen octahedra. In the Raman spectra of the crystals, the width of the line at a frequency of 876 cm–1, which corresponds to stretching modes of the oxygens in the BO6 octahedra, has been shown to increase considerably, which may be due to changes in the character of bonding in the B–O–B bridges in response to changes in the Zn concentration in the crystals. The gradual increase in the electro-optical coefficients of the LiNbO3:ZnO crystals with increasing zinc concentration can be accounted for by changes in the ionic contribution to these bonds.

Structure of amorphous oxide Al2O3: Results of a molecular-dynamics experiment

The structure of amorphous aluminum oxide was simulated by the molecular-dynamics method. A random distribution of Al3+ and O2− ions over the volumes of cubes with sides of 21 and 24 Å was used as a starting configuration. The character of the distribution of cations in the anion subsystem was analyzed. It was shown that formation of voids in model clusters is possible when the average electron density is underestimated

Short range order in powder of amorphous anodic yttrium oxide

The characteristics of the short-range order in a powder of amorphous yttrium oxide obtained by anodic oxidation are determined by the Finbak-Warren method. It is established that the first coordination number equals seven. Amorphous oxide is built by irregular coordination polyhedra characteristic of the hexagonal and monoclinic modifications of yttrium oxide.

Structure and properties of ceramic solid solutions LixNa1 − xTayNb1 − yO3 (x = 0–0.05, y = 0–0.04)

The structure of Li0.03Na0.97TayNb1 − yO3 ceramic solid solutions and the processes of its disordering with a change in composition and temperature have been studied by full-profile X-ray diffraction analysis and Raman spectroscopy. It was established that at room temperature the structure of Li0.03Na0.97Ta0.05Nb0.95O3 solid solutions is close to the NaNbO3 structure and has a space group P21ma with four formula units per unit cell. It was shown that the oxygen octahedra in the LixNa1−xTa0.1Nb0.9O3 solid solutions (0, 0.15, 0.03, 0.04, 0.05) are slightly distorted and their geometry is identical to that of octahedra in the NaNbO3 structure. The temperature dependence of the intensities of lines in the Raman spectrum of Li0.03Na0.97Ta0.4Nb0.6O3 solid solutions corresponding to vibrations of Li+ and Na+ cations in the cuboctahedral structural voids revealed a strong disordering in the alkali metal sublattice at a temperature above 322°C. This may indicate the essential stepwise increase in the Li+ cation mobility and may result in a change in the kinetic and energetic characteristics of ion charge transport.

Influence of ultrafast quenching on the structure of Li 0.12 Na 0.88 Ta y Nb 1 – y O 3 ceramics obtained by solid-phase synthesis

A technology of perovskite-type Li0.12Na0.88TayNb1 – yO3 ceramic solid solutions based on sodium and lithium niobates and tantalates and a method of their ultrafast quenching have been presented. The influence of quenching on the structure of ceramic samples and the variations in crystallographic and fine structure parameters have been studied. It has been found that ultrafast quenching results in a preferred orientation of crystallites, severe local microstrains, and changes in the atomic structure of Li0.12Na0.88TayNb1 – yO3 ceramics.

Research of physicochemical properties and structure of strongly doped LiNbO 3 :ZnO ([ZnO] ~ 4.02–8.91 mol %) crystals

In LiNbO3:ZnО crystals grown from melts containing ~4.0–9.0 mol % ZnO, the evolution of structure was studied, the lattice periods were detected, and the models of atomic structure were analyzed. Raman spectroscopy and full-profile analysis of XRD patterns were used to obtain the results. The rise in ZnO concentration in the melt from 4.0 to ~6.99 mol % leads to the decrease in the unit cell volume of the crystals. The further rise in ZnO concentration in the melt to ~7.8 mol % results in the increase in the unit cell volume of the crystals. Refinement of the profile characteristics of XRD patterns and structural characteristics of the researched crystal samples was performed by the Rietveld method using the PDWin software package. All samples were considered single-phase, taking into consideration the absence of intense bands coinciding with the lithium niobate bands. Zn2+ cations were detected to occupy Li sites (which are vacant in the congruent LiNbO3 crystal). In this case, Nb vacancies are absent. Zinc displaces all excess Nb atoms in Li sites. In the sample grown from melt with ~6.12 mol % ZnO. In this case, Li vacancies and electroneutrality stay the same in the sample. Thus, NbLi antistructure defects are absent in the LiNbO3:ZnО crystal (~6.12 mol % ZnО in the melt). In LiNbO3:ZnО crystals with higher ZnO concentration, NbLi antistructure defects appear again. In this case, the concentration of Zn in Li sites almost coincides with the one in the LiNbO3:ZnО crystal. Unit cell parameters are equal in crystals grown from melts with ~7.8 and ~6.76 mol %. The biggest changes in the Raman spectra of these crystals are observed in the regions of vibrations of cations (200–300 cm–1) located in oxygen octahedra ВО6 (В: Nb5+, Li+, Zn2+) and in the region of vibrations of oxygen atoms in oxygen octahedra (500–900 cm–1). This indicates a change in order of alteration of intrinsic, doping cations and vacancies along the polar axis and deformation of oxygen octahedra during doping. This corresponds to anisotropic expansion of oxygen octahedra along the polar axis in LiNbO3:ZnО crystals.

Hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I) from X-ray study

X-ray diffraction data on powder and single-crystal samples were used to determine the crystal structure of hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I): monoclinic system, sp. gr. P21/n, and Z = 2. Two molecules of N oxide of 2-(4-dimethylaminostyryl)quinoline are bound through a hydrogen atom located at the center of symmetry, thus forming a complex cation.