Yu. D. Tret'yakov

UV-shielding property, photocatalytic activity and photocytotoxicity of ceria colloid solutions.

UV-shielding property, photocatalytic activity and cytotoxicity (including photocytotoxicity) of citrate-stabilized ceria colloid solutions were studied. It was established that UV-shielding property (namely, the sun protection factor, the critical absorption wavelength and the UVA/UVB-ratio) of ceria nanoparticles are as good as those of titanium dioxide and zinc oxide nanoparticles. It was further demonstrated that ceria nanoparticles possesses substantially lower photocatalytic activity, which additionally decreases upon decrease in ceria particle size. It was found that colloid ceria solutions are non-toxic to mouse fibroblasts (L929) and fibroblast-like cells of African Green monkey (VERO). Moreover, ceria nanoparticles are capable to protect these cells from UV-irradiation-induced damage. It was proposed that nanocrystalline ceria could be used not only as UV-blocking material, but also as prophylactic and even therapeutic compound for sunburns treatment.

An electrochemical study of high-temperature stability of compounds between the rare earths and copper oxide☆

Abstract Equilibrium conditions for formation of the compounds CuLn2O4 (Ln = La, Nd, Sm, Eu, Gd) and Cu2R2O5 (R = Tb, Dy, Er, Yb, Y, In) were studied in galvanic cells with solid electrolyte ZrO2 (Y2O3) in the temperature range 950–1150°C. The results, together with results of a study of the equilibrium CuOCu2O, were used to calculate the ΔG° of formation of the double oxides from CuO and the Ln2O3 (In2O3, Y2O3) as listed above. We found a decrease in the stability of the compounds CuLn2O4 relative to the initial oxides in the sequence LaGd and an increase in the stability of Cu2Ln2O5 in the sequence TbYb. The results are discussed on the basis of special features of the crystalline structure of the compounds examined.

On the stability region and structure of the Nd1+xBa2−xCu3Oy solid solution

Abstract We studied the low and upper stability boundaries and the structure evolution of the Nd 1+ x Ba 2− x Cu 3 O z solid solution along its single-phase field. It was found that in oxygen the limit of the solid solution extends up to Nd 1.9 Ba 1.1 Cu 3 O z at 950–1050°C while at lower and higher temperatures it becomes narrower. In nitrogen atmosphere the substitution range is much smaller and x does not exceed 0.3 at 800°C. The replacement of Ba 2+ by Nd 3+ is accompanied by decreasing both a and c lattice constants of quenched samples. At the same time in oxygen at x ≥ 0.6 ordering phenomena occur leading to the orthorhombic distortion of the tetragonal subcell. A model of the solid solution crystal structure with a B-centered unit cell and lattice parameters a = 2 a sub , b = b sub and c = 2 c sub was suggested and refined.

Flux pinning improvement in Bi-2212 silver sheathed tapes with submicron SrZrO3 inclusions

Abstract Silver sheathed tapes of Bi-2212 undoped and doped with SrZrO 3 have been prepared, using co-precipitated oxalates as precursors. Thermal treatment conditions have been optimised, varying the maximum processing temperature T max . A comparative study on thermal treatment conditions, microstructure, and flux pinning properties for doped and undoped samples has been performed in order to evaluate the effect of SrZrO 3 addition. The doped samples contain SrZrO 3 submicron particles, appearing as aggregates included between Bi-2212 lamellae with a Cu-free phase and the rest of the liquid, and also distributed inside Bi-2212 grains. The presence of SrZrO 3 surplus leads to higher critical current densities in samples prepared in a wide T max range; in addition, the lowest T max , at which high J c can be obtained, becomes 5 deg lower (875°C). At T = 5 K critical currents for all the samples are of the order of 10 5 A/cm 2 and are independent of doping, while at 60 K doped samples exhibit roughly two times higher J c in zero field and more than an order of magnitude higher J c at H = 40 mT. A magnetisation decay study reveals that samples with SrZrO 3 surplus have a larger fraction of pinning centres with high energy. The enhanced pinning properties can be related to the finely dispersed zirconate inclusions found in the superconductor matrix.

Nonstoichiometry and defect structures in copper oxides and ferrites

Abstract The stoichiometry ranges of Cu2O1 + γ, CuO1 + γ, Cu0.984Fe2.016O4 + γ, Cu1.011Fe1.989O4 + γ, and Cu0.551Fe2.449O4 + γ were established by high temperature electrochemical measurements in a stabilized zirconia electrolyte cell. The results were consistent with neutral oxygen vacancies for oxygen deficit and neutral cation vacancies for oxygen excess in cuprite, neutral oxygen vacancies in Cu1.011Fe1.989O4 + γ and Cu0.551Fe2.449O4 + γ, neutral cation vacancies in Cu0.984Fe2.016O4 + γ and neutral associations of interstitial copper atoms in cupric oxide. The defect structures of these compounds were derived from the consideration of equilibrium with respect to oxygen between the solid and the gas phase. The absolute magnitudes of nonstoichiometry, defect concentrations and the enthalpy of defect formation were calculated. The enthalpies of the formation of Schottky defects in “Cu2O” and “CuFe2O4” were calculated.

Preparation of ordered magnetic iron nanowires in the mesoporous silica matrix

Abstract We report the synthesis of magnetic nanocomposites using mesoporous silica as a host material. Iron nanoparticles were incorporated into the pores of mesoporous silica. During the synthesis, a hydrophobic metal complex, Fe(CO)5, was introduced into the hydrophobic part of the as-prepared mesoporous silica–surfactant composite. The suggested method results in the formation of iron nanowires inside the silica framework. Particles shape and size are in good agreement with the shape and size of the pores. Particles are uniform and well ordered in the silica matrix. Thus, mesoporous silica serves as nanoreactor for the formation of Fe-nanoparticles. The magnetic susceptibility measurements indicate superparamagnetic properties of all samples. This approach leads to functional materials with nanosized active elements in amorphous silica matrix, which could find application as high-density data storage devices.

Investigation of some chalcogenides with spinel structure

Abstract The unusual combination of magnetic, semiconducting, and optical properties of the chalcochromites and other chalcogenide phases with spinel structure AB2X4 has attracted considerable attention for researchers (1–3). Although the physics of magnetic semiconductors is based on highly developed theoretical models and numerous experiments, the physical chemistry of these materials has many gaps. Knowledge of the thermal stability of the chalcogenide spinels, of the equilibrium conditions of their formation, and of their thermodynamics is lacking, although extremely important for the synthesis and thermal processing of single crystals and polycrystalline materials of the AB2X4 type. This paper presents the results of a study of the thermal stability and thermochemical, thermodynamic, and crystallochemical properties of the chalcochromites MeCr2X4 (Me = Cd, Co, Zn, Fe, Cu; X = S, Se, Te), thiocobaltites MeCo2S4 (Me = Cu, Co), thiorhodites MexRh3−xS4 (Me = Cu, Co, Fe), thioaluminates MeAl2S4 (Me = Zn, Cr), and solid solutions based on these. An attempt is made to show how much the investigated properties influence the magnetic and electrical properties of the chalcogenide spinels. This work is a continuation of the systematic investigation of chalcospinels, including, in particular, nonstoichometry and defect formation in the chalcochromites (4–7) homo- and heterovalent replacement in the chalcochromites (6, 8), and compound chalcochromites with replacement in the cation sublattice (9–11).

Nanocrystalline ceria based materials—Perspectives for biomedical application

Nanocrystalline ceria possesses a unique complex of physical and chemical properties making it highly bioactive material. In this review, modern data on the action of nanocrystalline ceria on cells, micro- and macroorganisms are analyzed. Special attention is paid to the analysis of the factors affecting protective properties of CeO2 with respect to the living systems.

The structure of 1D CuI crystals inside SWNTs.

Nanocomposites consisting of one‐dimensional CuI crystals inside single‐walled carbon nanotubes were obtained using the capillary technique. high‐resolution transmission electron microscopy investigations of the atomic structure of the encapsulated 1D CuI crystals revealed two types of 1D CuI crystals with growth direction <001> and relative to the bulk hexagonal CuI structure. Atomic structure models were proposed based on the high‐resolution transmission electron microscopy images. According to the proposed models and image simulations, the main contrast in the 1D crystal images arises from the iodine atoms whereas copper atoms, with lower atomic number giving lower contrast, are thought to be statistically distributed.

Chemical Design of Magnetic Nanocomposites Based on Layered Double Hydroxides

Chemical modification of anion-substituted layered double hydroxides (LDHs) was used for the preparation of anisotropic magnetic nanocomposites. The method combines the simplicity of chemical methods and the possibility to prepare two-, one-, or zero-dimensional nanoparticles in oxide/hydroxide matrices. An LDH structure consists of positively charged hydroxide layers bonded with negatively charged anions, which occupy the interlayer space. During chemical reactions of anions in the interlayer space, reaction zone is spatially constrained by the hydroxide layers, giving rise to the conditions similar to those in two-dimensional nanoreactors, such as Langmuir–Blodgett films and self-assembling monolayers. Here we used LDH precursors for the preparation of the Fe- and Ni-based nanocomposites. The precursors were obtained by intercalation of ethylenediaminetetraacetate (edta) complexes of Fe(III) or Ni(II) into the Mg–Al LDH. Substituted LDHs were reduced by H2 to give metal nanoparticles entrapped into the inert Mg–Al oxide matrix. Reduction of anion-substituted LDHs with different content of anionic complexes (and ratio Mg/Al in matrix) occurs at a relatively low temperature (∼600°C) and results in the formation of metal nanoparticles with different morphology and sizes. The formation of anisotropic metal nanoparticles in the former case is believed to be due to the spatial constraints of the reaction zone and their formation occurs simultaneously with buckling of hydroxide layers.