Preparation and characterization of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3-δ</Subscript> thin-film membrane on porous support by dip-coating method

Perovskite-type La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) thin-film membrane prepared by modified Pechini sol–gel process, was successfully deposited on porous support of similar composition using dip-coating method. Fine grain and crack-free film with perovskite structure was obtained at sintering temperature of 800 °C and dwelling time of 60 min. The cross-sectional image indicated that LSCF6428 thin-film membrane coated on the porous support showed excellent adhesion to the support with uniform thickness. The minimum dense layer thickness obtained by dip-coating method was around 0.5 μm. It was found that the oxygen permeability of the supported thin film was lower than that of the perovskite support, which indicated that the pores of the support were reduced by thin-film deposition on the support surface. The reduction in the pore size led to the more selective permeation mechanism contributes to the overall permeation. Successful deposition of LSCF6428 thin-film membrane on porous support can be considered as a promising technique for the preparation of oxygen separation membrane.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Preparation and adsorption properties of magnetic Co<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>–chitosan nanoparticles

Magnetic chitosan microspheres were prepared by the emulsification cross-linking technique in the presence of glutaraldehyde as cross-linking agent, liquid paraffin as dispersant, and Span-80 as emulsifier. The optimal cross-linking time and Co_0.5Ni_0.5Fe₂O₄: chitosan ratio were determined. The morphology of particles was studied by different techniques. The adsorption characteristics were studied and the effect exerted by the initial concentration of methyl orange, the time of cross-linking, and the amount of the adsorbent was determined. It is found that the product obtained at the Co_0.5Ni_0.5Fe₂O₄: chitosan ratio 1: 4 and the crosslinking time 5 h has the uniform morphology. At room temperature, the Co_0.5Ni_0.5Fe₂O₄–chitosan magnetic composite has maximal adsorption for methyl orange at the dosage 20 mg.     

Preparation and characterization of Ba<Subscript>2</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>12</Subscript>O<Subscript>22</Subscript> ferrite via glucose sol–gel method

Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) was synthesized by sol–gel method using glucose as chelating agent. X-Ray diffraction studies indicate that sintering temperature as low as 950 °C is sufficient to produce Co₂Y ferrites. Co₂Y ferrites calcined at 1,000 °C exhibit good magnetic prosperities in high frequency, with the resonance frequency up to 11 GHz and intrinsic permeability about 5 even at 6 GHz. The heat-treated temperature dependence of coercivity, initial permeability and resonance frequency is close related to the particle shape and size.     

Effect of the Copper Oxide Sintering Additive on the Electrical and Electrochemical Properties of Anode Materials Based on Sr<Subscript>2</Subscript>Fe<Subscript>1.5</Subscript>Mo<Subscript>0.5</Subscript>O<Subscript>6–δ</Subscript>

The effect of introducing 1–3 wt % copper oxide sintering additive on the electrical and electrochemical characteristics of promising anode materials for solid oxide fuel cells based on Sr₂Fe_1.5Mo_0.5O_6–δ was studied. The total conductivity increases with increasing amount of copper oxide. The maximum conductivity in humid hydrogen at 800°C, 45 S cm^–1, was reached on introducing 3 wt % CuO. The sintering additive enhances the electrochemical activity of Sr₂Fe_1.5Mo_0.5O_6–δ and Sr₂Fe_1.5Mo_0.5O_6–δCe_0.8Sm_0.2O_1.9 anodes. A decrease in the sintering temperature of the anodes containing CuO with the electrolyte based on lanthanum gallate directly correlates with the electrochemical activity of the anodes. The minimum value of the polarization resistivity, 0.15 Ω cm² at 800°С in a humid hydrogen atmosphere, was obtained for the composite anode with 3 wt % CuO sintered at a temperature of 1050°С.     

Magnetic properties of binary and ternary mixed metal oxides NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and Zn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> doped with rare earths by sol—gel synthesis

The spinel-type ferrites NiFe₂O₄ and Zn_0.5Ni_0.5Fe₂O₄ modified by lanthanide ions Eu³⁺ and Tb³⁺ were prepared by a sol—gel process with propylene oxide as a gelating agent. The phase homogeneity of the samples was tested by XRD and Mössbauer spectroscopy. Transmission electronic microscopy used for characterisation of the morphology of the samples revealed nanosized powdered samples with a narrow distribution of particle sizes. It was noted that the presence of Ln³⁺ ions influenced the magnetic properties of nanosized NiFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄ ferrites. The dependence of the magnetic properties of the samples on the rare-earth doping may be explained by the different grain sizes. The saturation magnetisation tends to decrease with increasing rare-earth doping and decreasing crystallite size. A similar trend was observed for the coercive field, with the exception of the Tb³⁺-doped Zn_0.5Ni_0.5Fe₂O₄ where it remained the same as in the pure ferrite.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Impedance Study of the Conductivity of Solid Oxide Electrolyte Films SrZr<Subscript>0.95</Subscript>Y<Subscript>0.05</Subscript>O<Subscript>3–δ</Subscript> and CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript>

Information on the across-plane conductivity of films of solid-oxide electrolytes SrZr_0.95Y_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ deposited on ion-conducting supports is acquired by the impedance method. It is shown that the support/film interface and the intergrain boundaries considerably affect the across-plane charge transfer in the film. The effect of the crystallographic orientation of the YSZ support on the microstructure and conductivity of the CaZr_0.9Y_0.1O_3–δ electrolyte film is demonstrated.     

Effects of acid treatment on electrochemical properties of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·LiNi<Subscript>0.5</Subscript>Co<Subscript>0.45</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>2</Subscript> cathode materials

A new composite, Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂, can be synthesized by a solid-state method and preconditioned with 5 wt% HCl, H₂SO₄, or H₃PO₄ solution to achieve H⁺/Li⁺ exchange. The effects of acid treatment on the structure, morphology, and electrochemical properties of Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ cathode materials are analyzed. The X-ray powder diffraction patterns imply that the hexagonal α-NaFeO₂ structure (space group R\(\bar{3}\)m) of the materials is not changed by the acid treatment. The scanning electron microscope images show that particles become spherical with smooth surfaces after acid treatment, and the Brunauer–Emmett–Teller analysis reveals that the specific surface area increases. The charge–discharge test demonstrates that acid-treated Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ cathode materials deliver higher initial coulombic efficiencies than untreated material, owing to the improvement of the catalytic reduction activity of oxygen released during the initial charge process. Furthermore, Li₂MnO₃·LiNi_0.5Co_0.45Fe_0.05O₂ treated with HCl displays the best electrochemical performance, with the acid treatment improving the initial coulombic efficiency from 66.0 to 82.2%. Thus, acid treatment can effectively improve the electrochemical performance of electrode materials in Li-ion batteries.     

Gel formation specifics in the synthesis of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> by the glycine–nitrate method

The gel formed in the synthesis of Mg(Fe_0.8Ga_0.2)₂O₄ powder from corresponding metal nitrates and glycine was studied by thermal and IR spectral analyses. Being a bidentate ligand, glycine was established to initiate the gel combustion reaction resulting in the oxide of the above composition. Based on the data on ΔH₂₉₈° and Cp of the reagents and reaction products, the thermodynamic parameters of this process were calculated.     

Synthesis,microstructure, and electric properties of CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3 – δ</Subscript> films obtained on porous SrTi<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3 – δ</Subscript> supports

Compact CaZr_0.9Y_0.1O_3–δ (CZY) film on a porous SrTi_0.8Fe_0.2O_3–δ (STF) support is obtained using the technique of deposition from solutions of inorganic salts in ethanol. According to the data of scanning electron microscopy (SEM), the film has a nanoporous granular structure with the grain size of 0.2 to 1 μm. The thickness of the CZY film on the STF support is about 3 μm after 15-fold solution application. The results of studying the elemental composition showed that elements of the support diffuse into the film in the course of synthesis. Analysis of the data of impedance spectroscopy shows that conductivity of the CZY film is limited the grain bulk. It is assumed that the comparatively low conductivity activation energy of the film (50.3 kJ/mol) is due to diffusion of elements of the STF support that results in variation of the film composition and properties.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Influence of A-site deficiencies in the system La<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>Ga<Subscript>0.8</Subscript>Mg<Subscript>0.2</Subscript>O<Subscript>3−δ</Subscript> on structure and electrical conductivity

In this study, the A-site-deficient ABO₃ perovskites La_0.9–x Sr_0.1Ga_0.8Mg_0.2O_3– with x=0.025, 0.05, 0.075, 0.1, and 0.2 were prepared by conventional solid state reactions. X-ray investigations were carried out in order to determine the influence of the A-site deficiencies on the structure. The electrical conductivities were measured as a function of both temperature and oxygen partial pressure in ranges 500–1000 °C and 0.2–10^–6 atm, respectively. Only for small x values were single phases obtained. All compositions with A-site deficiencies exhibit a lower conductivity compared to the stoichiometric compound. It is shown by SEM micrographs that the sample morphology is changed by an A-site-deficient preparation as well. For A-site-deficient compositions, a reduction of the grain size is observed, most likely due to impurity inclusions in the grain boundaries.     

Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Au core–shell nanoparticles

A new two-step synthesis of Fe₃O₄@Au core–shell nanoparticles stabilized in polyethylene glycol is described. The nanoparticles were characterized by transmission electron microscopy, X-ray powder diffraction, UV and Mössbauer spectroscopy. Fe₃O₄@Au nanoparticles featured both optical properties (they featured a plasmon resonance band) and magnetic properties (they responded to an external magnetic field), typical of individual gold and magnetite nanoparticles, respectively.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>·C and ZrO<Subscript>2</Subscript>·Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>·C nanostructures: Synthesis and characterization

A procedure for the synthesis of carbon-encapsulated multilayer magnetite and zirconium oxide–magnetite nanoparticles that form porous nanostructures, for use as biocompatible sorbents, is proposed. The properties, composition, dimensions, particle shapes, surface morphology, and magnetic characteristics of the products are studied.     

Influence of synthesis route on morphology and conduction behavior of BaCe<Subscript>0.8</Subscript>Y<Subscript>0.2</Subscript>O<Subscript>3−δ</Subscript>

In this article, the role of the preparation route and calcinations temperature on the thermal expansion and conductivity of BaCe_0.8Y_0.2O_3−δ (BCY) has been studied. In particular, the samples were synthesized by means of the solid-state reaction and by a sol–gel route. BCY has been suggested as proton conducting electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Proton conductivity strongly depends on the densification of the material as well as the crystal structure, which is generally influenced by the preparation procedure. It was found that a single phase material could be achieved at 1000 °C for the samples prepared through the sol–gel route with ~96% packing density. In case of ceramic route, single phase could be obtained at higher temperatures (1200 °C) and does not lead to good density values. The ceramic synthesis produces BCY material in cubic symmetry where as the gel–citrate complexation route leads to homogenous orthorhombic BCY. The conductivity measurements of sample synthesized by two different routes were investigated by means of impedance spectroscopy and electron microscopy. A comparative study of thermal expansion behavior of BCY synthesized by different route was carried out.     

Thermal behavior of Co<Subscript>x</Subscript>Fe<Subscript>3−x</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites obtained by a modified sol–gel method

The thermal behavior of Co_xFe_3?xO₄/SiO₂ nanocomposites obtained by direct synthesis starting from nonahydrate ferric nitrate and hexahydrate cobalt nitrate in different ratios with and without the addition of 1,4-butanediol was studied. For the synthesis of Co_xFe_3?xO₄ (x = 0.5–2.5) dispersed in the silica matrix a wide Co/Fe molar ratio was used. The decomposition processes, formation of crystalline phases, gases evolvement and mass changes during gels annealing at different temperatures were assessed by thermal analysis. The absence of succinate precursor and a low mass loss were observed in the case of the gel obtained in the absence of 1,4-butanediol. In case of gels obtained using a stoichiometric ratio of Co/Fe, no clear delimitation between Co and Fe succinates was observed, while for samples with a Fe or Co excess, the formation of the two succinates was observed. The evolution of the crystalline phase after annealing (673, 973 and 1273 K) investigated by X-ray diffraction analysis and Fourier transformed infrared spectrometry revealed that in samples with Fe excess, stoichiometric Fe/Co ratio or low Co excess, the cobalt ferrite (CoFe₂O₄) was obtained as a single phase, while in samples with higher cobalt excess, olivine (Co₂SiO₄) as a main phase, cobalt oxide and CoFe₂O₄ as secondary phases were obtained after annealing at 1273 K. The SEM images confirmed the nanoparticles embedding in the silica matrix, while the TEM and X-ray diffraction data showed that the obtained nanoparticles’ size was below 10 nm in most samples.     

Electronic and ionic zeebeck coefficients in mixed conductors of Ag<Subscript>0.25–δ</Subscript>Cu<Subscript>1.75</Subscript>Se,Ag<Subscript>1.2–δ</Subscript>Cu<Subscript>0.8</Subscript>Se

The paper presents the studies of ionic and electronic Zeebeck coefficients and electronic conductivity in nonstoichiometric Ag_0.25–δCu_1.75Se, Ag_1.2–δCu_0.8Se solid solutions existing on the basis of the cubic phase of copper selenide. It is shown that Ag_1.2–δCu_0.8Se is a bilateral variable composition phase manifesting inversion of the sign of predominant charge carriers under variation of the chemical composition by silver within the homogeneity region. Mobilities of electrons and electron holes are estimated on the basis of the concentration dependences.     

In-situ construction of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoarrays on La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3-δ</Subscript> electrodes for intermediate temperature solid oxide fuel cells

Novel NiCo₂O₄ nanoarrays have been in-situ grown on a La_0.8Sr_0.2MnO_3-δ(LSM) cathode through a hydrothermal method, which presents the enhanced electrochemical performances of the LSM cathode for the intermediate temperature solid oxide fuel cells. XRD and SEM have been used to characterize phase structure and morphology of NiCo₂O₄ nanoarrays. The LSM cathode, modified by the NiCo₂O₄ nanoarrays, exhibits excellent electrochemical performances compared with the bare LSM cathode. The maximum peak power density of single cell, based on the NiCo₂O₄ nanoarrays modified the LSM cathode, reaches 957 mW cm^?2 at 800 °C, which is almost two times higher than that for the cell based on the bare LSM cathode.