T. S. Chernaya

Atomic structure of Sr0.75Ba0.25Nb2O6 single crystal and composition-structure-property relationin (Sr,Ba)Nb2O6 solid solutions

The structure of the Sr0.75Ba0.25Nb2O6 single crystal has been investigated by x-ray diffraction. The occupancies of the Ba and Sr sites in two structural channels are determined. It is found that these sites are split in the large (pentagonal) channel. A qualitative correlation is revealed between the smearing of the phase transition and the displacement of the Sr atom from the m symmetry plane in the pentagonal channel at different [Sr]/[Ba] ratios. The degree of acentricity of the NbO6 octahedra is analyzed as a function of the [Sr]/[Ba] ratio.

Threshold concentrations in zinc-doped lithium niobate crystals and their structural conditionality

On the basis of precise X-ray diffraction study of lithium niobate single crystals of congruent composition and four zinc-doped (at 2.8, 5.2, 7.6, and 8.2 mol %) crystals, structural conditionality of the threshold concentrations of the dopant has been established. At these concentrations, the mechanism of zinc incorporation into crystal changes. As the zinc concentration increases, this element first substitutes excess niobium, localized in lithium positions, with a simultaneous decrease in the number of vacancies in these positions. Then zinc substitutes lithium with formation of new lithium vacancies. When a certain limit on the number of vacancies is reached, zinc begins to substitute niobium in its main positions. This process is naturally accompanied by a decrease in the number of vacancies to their complete disappearance and formation of a self-compensating crystal. The character of the dependence of the crystal physical properties on the dopant concentration changes specifically when the impurity concentration passes through the threshold values.

Zn Atoms in Lithium Niobate and Mechanism of Their Insertion into Crystals

Precision X-ray structural studies were carried out for LiNbO3:Znx single crystals with x=0.0, 2.87, 5.20, and 7.60 at. %. It was found that the insertion of the Zn atoms into the Li position was accompanied by a decrease in the concentration of intrinsic NbLi defects. At x=7.6%, the Zn atoms change their locations in the lattice and partially occupy the Nb positions. This clarifies the structural nature of the “threshold” Zn concentration, which manifests itself as singularities in the concentration dependences of various optical properties. The structural origin of the threshold concentration is likely a common feature of all nonphotorefractive impurities (Mg, Zn, In, and Sc) in LiNbO3. A change in the intrinsic defect structure of the LiNbO3 crystals with different Zn concentrations is discussed.

Investigation of the structural conditionality for changes in physical properties of K3H(SO4)2 crystals

AbstractWith the aim of elucidating the nature of anomalies in the physical properties of K3H(SO4)2 crystals that arise as the temperature grows, the dielectric and optical properties of the crystals are studied, an X-ray diffraction analysis of single-crystal and polycrystalline specimens are performed, and the morphology and chemical composition are studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result of the studies performed, a phase transition from the phase with the monoclinic symmetry (space group C2/c) to the phase with the trigonal symmetry (space group R

Synthesis and crystal structures of coordination compounds of pyridoxine with zinc and cadmium sulfates

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X-ray and neutron diffraction study of the defect crystal structure of the as-grown nonstoichiometric phase Y0.715Ca0.285F2.715

m) is found in a number of K3H(SO4)2 specimens at a temperature of ≈457 K, the responsibility of the dynamically disordered hydrogen-bond system for the rise of high proton conductivity in the high-temperature phases of the crystals of this family is confirmed, and data on the solid-phase reactions proceeding at high temperatures are obtained.

Relationship between the defect structure and fluorine-ion conductivity of La1 − ySryF3 − y (0 ⩽ y ⩽ 0.15) crystals according to X-ray and neutron diffraction data

Precision X-ray structural studies of the La3Nb0.5Ga5.5O14 and Sr3Ga2Ge4O14 single crystals were carried out. The space group P321 was confirmed. The anomalous X-ray scattering was taken into account to establish the absolute structures (chirality) of the crystals; they proved to be of different sign. The structural features responsible for the optical activity of crystals were revealed, and the dependence of the magnitude and sign of specific rotation on the structural parameters of these compounds were determined.

Temperature-induced changes in the single-crystal structure of K9H7(SO4)8 · H2O

The pyridoxine complexes with zinc and cadmium sulfates are synthesized. The IR absorption spectra and thermal behavior of the synthesized compounds are described. Crystals of the [M(C8H11O3N)2(H2O)2]SO4 · 3H2O (M = Zn, Cd) compounds are investigated using X-ray diffraction. In the structures of both compounds, the M atoms are coordinated by the oxygen atoms of the deprotonated OH group and the CH2OH group retaining its own hydrogen atom, as well as by two H2O molecules, and have an octahedral coordination. The nitrogen atom of the heterocycle is protonated, so that the heterocycle acquires a pyridinium character. The cationic complexes form layers separated by the anions and crystallization water molecules located in between. The structural units of the crystals are joined together by a complex system of hydrogen bonds.