Yury D. Tretyakov

Complexes of Cu(II) with polyvinyl alcohol as precursors for the preparation of CuO/SiO2 nanocomposites

Abstract Cupric oxide (CuO) nanoparticles have been prepared in amorphous SiO2 matrix using a novel variant of sol-gel technique. The method is based on the polycondensation of a silica source (sodium silicate) in the presence of an aqueous solution containing complex of Cu(II) with polyvinyl alcohol (CuPVA). After gelation, polymeric complexes containing several thousands Cu atoms each are incorporated into the silica network forming a precursor, which is then annealed in oxygen to get rid of organic components. The formation of CuO nanoparticles was confirmed by electron diffraction studies. The size of nanoparticles can be controlled by varying [Cu2+]/[PVA] ratio in the precursor. Thus prepared CuO/SiO2 nanocomposites are characterized by high specific surface area as measured by capillary adsorption of nitrogen, suggesting their possible use in catalysis.

Planar SERS nanostructures with stochastic silver ring morphology for biosensor chips

Surface-enhanced Raman spectroscopy (SERS) of living cells has rapidly become a powerful trend in biomedical diagnostics. It is a common belief that highly ordered, artificially engineered substrates are the best future decision in this field. This paper, however, describes an alternative successful solution, a new effortless chemical approach to the design of nanostructured silver and heterometallic continuous coatings with a stochastic “coffee ring” morphology. The coatings are formed from an ultrasonic mist of aqueous diamminesilver hydroxide, free of reducing agents and nonvolatile pollutants, under mild conditions, at about 200–270 °C in air. They consist of 30–100 micrometer wide and 100–400 nm high silver rings composed, in turn, of a porous silver matrix with 10–50 nm silver grains decorating the sponge. This hierarchic structure originates from ultrasonic droplet evaporation, contact-line motion, silver(I) oxide decomposition and evolution of a growing ensemble of silver rings. The fabricated substrates are a remarkable example of a new scalable and low cost material suitable for SERS analyses of living cells. They evoke no hemolysis and reduce erythrocyte lateral mobility due to suitable “coffee ring” sizes and a tight contact with the silver nanostructure. A high SERS enhancement, characteristic of pure silver rings, made it possible to record Raman scattering spectra from submembrane hemoglobin in its natural cellular environment inside single living erythrocytes, thus making the substrates promising for various biosensor chips.

LuBa2Cu3O7–x thin films prepared using MOCVD

LuBa2Cu3O7–x thin films with Tc= 86–88 K were prepared by flash evaporation MOCVD on LaAlO3, SrTiO3, ZrO2(Y2O3) and NdGaO3 single-crystal substrates (deposition temperature 795 °C, partial oxygen pressure 1.35 Torr). Values for the critical current density jc(77 K., H= 100 Oe), of 9 × 105, 1.1 × 106 and 1.2 × 106 A cm–2 were measured for films on ZrO2(Y2O3), SrTiO3 and LaAlO3 respectively. The calculated magnitude of |ΔjcΔT| for LuBa2Cu3O7–x films on coherent substrates was found to be higher than that of YBa2Cu3O7–x films, indicating a more efficient magnetic flux pinning mechanism. The temperature dependence of conductivity fluctuations was considered in terms of a Lawrence–Donniach model and a 3D → 2D dimensional crossover was registered for the films on SrTiO3.

Bioresorbable carbonated hydroxyapatite Ca10−xNax(PO4)6−x(CO3)x(OH)2 powders for bioactive materials preparation

The purpose of this work was to find and investigate a correlation between the carbonate ion content in crystalline lattice and defect structure, and solubility of the materials; finally, to prepare the materials under study for in vitro tests. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO2, BET adsorption, were applied to determine the efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution,. It was shown that AB-type substitution prevails over other types with the carbonate content increase. According to in vitro tests, the bioactivity of the samples is correlated with the carbonate content in carbonate-doped hydroxyapatite due to accumulation of defects in carbonated hydroxyapatite nanocrystals.

Study on the superconducting composite material formation in the system Bi2Sr2CaCu2O8+x/Al-containing phases

Abstract Phase evolution in the BiSrCaCuAlO system was studied. Two Al-containing phases BiSr 1.5 Ca 0.5 Al 2 O z and (Sr 1− x Ca x ) 3 Al 2 O 6 ( x = 0.4 − 0.45) were determined to be chemically compatible with Bi 2.18 Sr 2 CaCu 2 O 8+ x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5 Ca 0.5 Al 2 O z was found to be in equilibrium only with the melt and the (Sr 1− x Ca x ) 3 Al 2 O 6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr 1.5 Ca 0.5 Al 2 O z ↔ (Sr 1− x Ca x ) 3 Al 2 O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + n BiSr 1.5 Ca 0.5 Al 2 O z and Bi-2212 + m (Sr 1− x Ca x ) 3 Al 2 O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5 Ca 0.5 Al 2 O z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr 1− x Ca x ) 3 Al 2 O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m (Sr 1− x Ca x ) 3 Al 2 O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.

Constrained growth of anisotropic magnetic δ-FeOOH nanoparticles in the presence of humic substances

Natural polyelectrolytes, humic substances, are suggested to control in situ growth of feroxyhyte nanoparticles of a highly reduced mean size and with enhanced colloidal stability in salt solutions. The feroxyhyte is formed as 2–5 nm thick and 20 × 20 nm wide nanoflakes due to the blocking of developing facets of feroxyhyte and constraints caused by diffusion limitations of ionic constituents across partially charged branches of humic substances.

CVD synthesis and SNMS characterization of thin films of ABO3 perovskite-type materials (PbTiO3, La(Sr)CoO3, La(Sr)MnO3, LaNiO3)

Abstract Powder flash evaporation and aerosol-MOCVD (organometallic chemical vapour deposition) methods were applied for the deposition of thin films and heterostructures of ABO 3 perovskite type-materials. It was shown that the plasma-SNMS (secondary neutral mass spectrometry) can be successfully used for the quantitative analysis of these thin films. High density ceramics were found to be good reference samples for such an analysis. It was shown that the interaction between PbTiO 3 thin films and La(Sr)CoO 3 (electrode material) is negligible under deposition conditions. The interaction between La(Sr)CoO 3 thin films and ZrO 2 (Y 2 O 3 ) substrate takes place only at the temperatures higher than 900 °C. La(Sr)MnO 3 thin films react with the Si substrate during deposition by aerosol-MOCVD with formation of a silicate layer. In the case of La(Sr)CoO 3 this reaction is retarded because of low oxygen partial pressure. This decrease of oxygen content in the gaseous phase near the substrate is caused by the catalytic oxidation of solvent (diglyme) at the surface of a La(Sr)CoO 3 film.

Fundamental chemical features of complex manganites and cuprates for advanced functional materials engineering

The existence of a tide relationship between fundamental chemical properties of either copper or manganese as 3d transition elements and advanced functional properties of related oxide materials is demonstrated using original experimental results. The complex role of ionic sizes, oxidation and spin states, and Jahn–Teller distortions is discussed in terms of the influence of these phenomena on the crystal structure, phase assemblage, microstructure, and physical properties of three key classes of modern copper- and manganese-containing materials (high-temperature superconductors, colossal magnetoresistive compounds, and 1d superionics), bringing up innovation technologies in electrical power engineering, micro- electronics, spintronics, magnetic field sensing, electrode materials, and fuel cells.

The synthesis of Bi(Pb)SrCaCuO superconductors with the use of separately precalcined precursors

The special features have been revealed of bismuth superconductors synthesis via Bi(Pb) Ca Cu O and Sr Ca Cu O precursors as compared with the method of direct mixing of oxides and carbonates. The latter method permits to obtain the ceramics with a T c (zero) of about 109 K containing the mixture of 2212 and 2223 homologue-phases rather rapidly but even after prolonged annealing the amount of 2212 homologue remains at the level of about 40%. The synthesis presuming separated precalcined precursors permits the formation of the superconducting high- T c phase for 80 h. This phase contains up to 94% of the 2223 homologue as a result of Ca bismuthates formation in easily fusible precursor, but Ca 2 CuO 3 and CuO impurities concentrate not in the bulk of the superconductor as with direct mixing, but on crystal surfaces, affecting greatly the resistive properties of ceramics obtained.

Cryochemically Processed Li2CuO2 for Lithium-Ion Batteries

Recent works demonstrated the growing interest to lithium cuprates as cathode materials for secondary lithium batteries. Li2CuO2, having orthorhombic structure (a=3,654 A, b=2,859 A, c=9,374 A) (Arai et al., 1998), is often considered as one of the most perspective among them, though many features of the phase formation mechanism and its relation to electrochemical properties remain underestimated.