Vol 52, No 8 (2016)

The three-dimensional geometric analysis carried out in this study has made it possible to clearly outline the homogeneity regions of solid solutions rich in magnesium and potassium oxides. Common elements in the structures of the zeolites (offretite, direnzoite, and ferrierite-Mg) have been identified and the factors responsible for the distinctions between their structures have been analyzed.

Photosensitive epitaxial n-CdSe layers with high structural perfection have been grown on mica (muscovite) crystals in a quasi-closed system. We have studied polar diagrams of sensitivity for the epitaxial n-CdSe layers on mica as four-contact position-sensitive semiconductor photodetectors. Position sensitivity characteristics of the epitaxial n-CdSe layers on mica have been determined.

The magnetic properties of CoCr₂S₄–Cu_0.5In_0.5Cr₂S₄ solid solutions have been studied in the temperature range 5–300 K at different ac magnetic field frequencies (100, 500, and 1000 Hz) and an amplitude of 79.6 A/m. We have determined the temperatures of the magnetic transformations in the system, identified their nature, and constructed the magnetic phase diagram of the solid solutions.

We have studied the local composition and nanoscale surface morphology of a calcium niobate, Сa₂Nb₂O₇, single crystal after thermally stimulated heterosegregation with the aim of identifying the mechanisms underlying the formation of a surface phase with the matrix composition. The identity of the compositions of the surface phase and matrix is accounted for in terms of a liquid-phase model for surface segregation, which includes diffusion, melting, and crystallization processes.

Atmospheric plasma spraying of powder materials has been used to produce thermal barrier coatings (TBCs) based on ZrO₂ stabilized with 7 wt % Y₂O₃, including coatings doped with neodymium and samarium oxides, for state-of-the-art and next-generation high-temperature gas turbine engines. Doping with neodymium and samarium oxides has been shown to reduce the thermal conductivity of the TBCs by 10–20%. At the same time, changes in the phase composition, crystal structure parameters, and microstructure of the TBCs during heat treatment at the service temperature lead to an increase in the thermal conductivity of all the coatings by 50–70%.

The formation of a unique hyper-kagome atomic order in the structure of the ordered spinel phase Na₃Ir₃O₈ has been analyzed in terms of the Landau theory of phase transitions. We have identified a critical six-component order parameter generating a phase transformation of the spinel parent phase to ordered P4₁32 (P4₃32) spinel-like enantiomorphs and examined the structural mechanism behind the development of hyper-kagome order and the detailed crystal chemistry of Na₃Ir₃O₈.

We have compared the intensity and shape of photoluminescence spectra of Tb³⁺ ions in mesoporous glasses, inorganic phosphors (terbium nitrate and terbium chloride hexahydrates), and coordination compounds (terbium benzoate, terbium o-phenoxybenzoate, and terbium terephthalate). The excitation sources used were a repetitively pulsed nitrogen laser with an emission wavelength of 337 nm and cw semiconductor light-emitting diodes with wavelengths of 369 and 385 nm. It has been shown that the highest photoluminescence intensity normalized by the percentage of terbium is offered by terbium terephthalate and terbium- doped mesoporous glass. We are thus led to conclude that introducing terbium terephthalate into the pores of mesoporous photonic glass and mesoporous photonic crystals is a promising approach for obtaining efficient laser operation in the green spectral region on the ⁵D₄–7F₅ transition of the terbium ion.

We have studied the radiation resistance of CaF₂:Yb³⁺ (3 mol % YbF₃) laser ceramics and a single crystal of similar composition (3.6 mol % YbF₃) exposed to gamma rays in a ⁶⁰Co source. The unirradiated samples have been shown to be similar in spectral characteristics. Even though irradiation leads to identical valence changes, Yb³⁺↔Yb²⁺, in the single crystals and ceramics, it produces characteristic defect centers in the ceramic samples, which are responsible for the observed marked differences in the rate of valence changes and the annealing rate of radiation-induced defects.

We have studied nonaqueous suspensions of Ce_0.8Sm_0.2O_1.9 (CSO), Ce_0.8Gd_0.2O_1.9 (CGO), and Се_0.8(Sm_0.75Sr_0.2Ba_0.05)_0.2O_2–δ (CSSBO) nanopowders produced by laser evaporation of a target. The nanoparticles were nearly spherical in shape and their average diameter was 9, 7, and 15 nm, respectively. Using ultrasonic processing, we obtained stable nanopowder suspensions in an isopropanol + acetylacetone mixed medium, investigated their particle size composition, evaluated their zeta potential as a function of pH, and obtained potentiometric titration curves. The starting nanopowder suspensions have been shown to be weakly acidic and have a rather high initial zeta potential. During titration of the nanopowder suspensions with 0.17 N KOH in isopropanol, no isoelectric point was observed. The maximum positive values of the zeta potential, favorable for electrophoretic deposition (EPD), were reached in weakly acidic media in the pH range 4–6. Using EPD, we obtained a coating from a stable self-stabilized CSSBO suspension (ζ = +31 mV, pH 4.0), which was then sintered in air at a temperature of 1400°C. Our results demonstrate that the starting nonaqueous suspensions of the CSO, CGO, and CSSBO nanopowders suit well for producing gas-tight, homogeneous solid oxide fuel cell coatings by EPD.