Growth and study of single crystals of (Na,K)NbO<Subscript>3</Subscript> solid solutions

(Na, K)NbO₃ crystals with a perovskite structure and a KNbO₃ content up to 40 mol % were grown from flux with the use of the solvent NaBO₂. The dielectric measurements of the crystals grown revealed phase transitions that had never been observed before in ceramic samples.     

Formation of a cluster structure in the PbZr<Subscript>1 – <Emphasis Type="Italic">x</Emphasis> </Subscript>Ti<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>O<Subscript>3</Subscript> system

Microdeformations of the crystal lattices in the phombohedral and tetragonal regions of the PbZr_1–xTi_xO₃ phase diagram have been calculated and their dependences on the titanium concentration have been constructed. Based on an analysis of these dependences, it has been concluded that tetragonal-phase clusters form in the range 0.11< x < 0.12 and rhombohedral-phase clusters form in the range 0.725 < x < 0.750.     

Ion conductivity,structural features,and multifractal properties of grain boundaries in CuCr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>2</Subscript>

The ion conductivity, crystal structure, and multifractal parameters of the sections of grain boundaries in CuCr_1?x V _x S₂ superionic conductors with 0 ≤ x ≤ 0.3 have been investigated. It is established that an increase in the surface area of grain boundaries and complication of their shape in such compounds facilitate ion transport. The effect of crystal structure peculiarities on the grain structure of these compounds has been revealed.     

Thermal reactions of organyl chalcogenides with α,β-unsaturated aldehydes

Thermal gas-phase reactions of acrolein, cinnamaldehyde, and benzaldehyde with diorganyl chalcogenides and diorganyl dichalcogenides were studied. Acrolein does not react with chalcogenides at 300–600°C but completely decomposes under reaction conditions. At 600–650°C, cinnamaldehyde reacts only with diorganyl selenides and diselenides to give benzoselenophene. Its highest yield (53%) is achieved in the reaction with dimethyl diselenide at 630°C and at an equimolar ratio of the reactant. The gas-phase reactions of benzaldehyde at 400–500°C afford chalcogen-containing derivatives of several types, among which thioanisole and its selenium or tellurium analogs predominate. The mechanisms of the above reactions were discussed in terms of homolytic substitution of the formyl group at unsaturated carbon atoms by chalcogenyl radicals.     

Crystal chemical simulation of low-permittivity ferroelectrics

It is shown that the uniform strain parameter of the unit cell of solid solutions of alkali metal niobates can be raised and their permittivity can drastically be decreased by isovalent superstoichiometric modification in the A subcell. The underlying mechanism is suggested. It is concluded that these findings are helpful in studying (simulating) piezoelectric ferroelectrics of practical value.     

Thermal stability and electrical conductivity of multiferroics BiFeO<Subscript>3</Subscript>/REEs

Ceramic samples of bismuth ferrite and solid solutions of Bi_{1 − x} A _x FeO₃ type (where A = Lu, Yb, Tm, Er, Ho, Dy, Tb, Gb, Eu, Sm, Nd, Pr, La; 0.05 ≤ x ≤ 0.20; Δx = 0.05) were prepared. Spectra of the real part of electrical conductivity were studied within the range 10⁻⁴–10⁻⁶ Hz. The dependence of the samples’ thermal stability and electrical conductivity on the size of the substituting ions was established.     

Phase analysis of high-temperature superconductors by selective dissolution combined with ICP-AES

Summary An apparatus for the selective dissolution as a chemical method of phase analysis and its operating conditions are described. Using ICP-AES as determination method an example for the YBCO system is found in the phase YBa_2–0.04Cu_3+0.03O_x and a BSCCO system is found in three phases of 35.6% Bi₂(Sr,Ca)_4–0.08Cu_3–0.05O_x, 30.1% Bi₂(Sr,Ca)_3–0.09Cu_2–0.08O_x and 34.3% Bi₂(Sr,Ca)_2–0.07Cu_1–0.05O_x.     

Changes in the structural parameters and molecular dynamics of polyhydroxybutyrate-chitosan mixed compositions under external influences

Differential scanning calorimetry (DSC), EPR probe analysis, large-angle X-ray diffraction (XRD), and UV spectroscopy are used to study the molecular dynamics and structure of hydroxybutyrate (PHB) copolymer, chitosan, and mixed compositions thereof upon thermal treatment in an aquatic medium. It is shown that, in mixed compositions, starting from 30% PHB, the correlation time increases by an order of magnitude, indicative of a sharp slowdown of the molecular mobility of the probe, and, concurrently, the degree of crystallinity decreases abruptly, as evidenced by DSC and XRD analyses. The diffusion coefficient of rifampicin in mixed compositions also decreases with increasing PHB content. A short-term (1 h) thermal treatment (at 70°C) in water results in an increase in the molecular mobility of the probe in the system. Crystallinity changes in complex ways.