Maria Gazda

Structural studies and melting of bismuth nanocrystals in reduced bismuth germanate and bismuth silicate glasses

Abstract Bismuth nanoclusters embedded in germanate glass matrices and surface layer of bismuth grains have been obtained by thermal treatment in hydrogen atmosphere of Bi 0.33 Ge 0.67 O 1.84 and Bi 0.57 Si 0.43 O 1.72 glass. The composite Bi-glasses were investigated by differential scanning calorimetry, X-ray diffraction and atomic force microscopy methods. A depression of the melting point of Bi from 544 to 387 K was found for nanosized bismuth particles embedded in glass and to 502 K when these are on the surface. It is shown that melting and solidification of bismuth nanocrystals induce a large change in surface conductivity of reduced glasses. A simple two-layer model of reduced glasses explains the evolution of surface layer and electrical properties of the materials during the reduction process.

Conductivity improvement of Ce0.8Gd0.2O1.9 solid electrolyte

Abstract Solid oxide fuel cells based on doped ceria electrolytes offer operating temperatures of ∼600 °C. During recent years much attention was aimed at successful powder preparation with high sinter activity and high conductivity. The properties of ceria electrolyte are very sensitive to impurities introduced during powder and electrolyte fabrication. One of the most successful and commercially available processes for the production of clean powders is based on the addition of several percent metallic cations that will react with impurities and segregate into the triple points of grain boundaries. In this work the results obtained from doping of CGO20 by 2% Ca and prepared by different routes were presented. The way of introducing Ca seemed to play an important role.

Influence of Sb-substitution on ionic transport in lanthanum orthoniobates

The results of ionic transport measurements for the lanthanum orthoniobate substituted with 10 and 30 mol% of antimony (LaNb0.9Sb0.1O4 and LaNb0.7Sb0.3O4) are presented and discussed. The influence of calcium co-doping on these properties has also been analysed. It has been shown that for the investigated material protonic conductivity predominates at temperatures up to 800 °C in oxidizing atmospheres under wet conditions. The maximum observed protonic conductivity reaches ∼10−4 S cm−1 at 800 °C (in humidified air); under dry conditions, the increasing influence of oxygen vacancies and holes is detected. Oxygen self-diffusivity has also been analysed by isotopic exchange to investigate the possible diffusion paths.

Tin oxide nanoparticles from laser ablation encapsulated in a carbonaceous matrix – a negative electrode in lithium-ion battery applications

This report concerns carbonaceous electrodes doped with tin(II) oxide nanoparticles. Tin nanoparticles are obtained by pulsed laser ablation in water. Crystalline nanoparticles have been encapsulated in a carbonaceous matrix formed after pyrolysis of a mixture consisting of tin/tin(IV) oxide nanoparticles and gelatine. The obtained material is characterized by means of X-ray diffraction, selected area diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Battery charging/discharging tests exhibit a capacity of 580 mA h g−1 for current densities of 100 mA g−1. The cycling performance of the material suggests that the tested nanocomposite can be used as an anode for lithium-ion batteries.

Graphene hydrogels with embedded metal nanoparticles as efficient catalysts in 4-nitrophenol reduction and methylene blue decolorization

Abstract Synthesis and characterization of the graphene hydrogels with three different metallic nanoparticles, that is Au, Ag and Cu, respectively is presented. Synthesized in a one-pot approach graphene hydrogels with embedded metallic nanoparticles were tested as heterogeneous catalysts in a model reaction of 4-nitrophenol reduction. The highest activity was obtained for graphene hydrogel with Cu nanoparticles and additional reaction of methylene blued degradation was evaluated using this system. The obtained outstanding catalytic activity arises from the synergistic effect of graphene and metallic nanoparticles. The hydrogel form of the catalyst benefits in the easiness in separation from the reaction mixture (for example using tweezers) and reusability.

Characterization of CaTi0.9Fe0.1O3/La0.98Mg0.02NbO4 composite

It has been recently shown that suitable asymmetric microstructures can be used to achieve microorganism separation. Here we study numerically how the separation process depends on the specific motility strategies of the microorganisms involved. Crucial properties such as the separation efficiency and the separation time for two bacterial strains are precisely defined and evaluated. In particular, the sorting of two bacterial populations inoculated in a box consisting of a series of chambers separated by columns of asymmetric obstacles is investigated and compared to that occurring in a box free of geometrical constraints.A composite of CaTi0.9Fe0.1O3 and electrolyte material, i.e. magnesium doped La0.98Mg0.02NbO4 was prepared and studied. The phase content and the sample microstructure was examined by an X-ray diffraction method and scanning electron microscopy. EDS measurements were done both for composite samples and the diffusion couple. The electrical properties were studied by four terminal DC method. The high-temperature interaction between the two components of the composite has been observed. It has been suggested that lanthanum diffused into the perovskite phase and substituted for calcium whereas calcium and niobium formed the Ca2Nb2O7 pyrochlore phase. At 1500°C very large crystallites of the pyrochlore were observed. Regardless of strong interaction between the composite components, its total conductivity was weakly dependent on the sintering temperature.

Perovskites in Solid Oxide Fuel Cells

Perovskite oxides comprise large families among the structures of oxide compounds, and several perovskite-related structures are also known. Because of their diversity in chemical composition, properties and high chemical stability, perovskite oxides are widely used for preparing solid oxide fuel cell (SOFC) components. In this work a few examples of perovskite cathode and anode materials and their necessary modifications were shortly reviewed. In particular, nickel-substituted lanthanum ferrite and iron-substituted strontium titanate as cathode materials as well as niobium-doped strontium titanate, as anode material, are described. Electrodes based on the modified perovskite oxides are very promising SOFC components.

Microstructural and electrical properties of Y0.07Sr0.93-x TiO3-δ perovskite ceramics

In order to find a relationship between electrical and microstructural properties, yttrium-doped strontium titanate (7 mol%) with various values of strontium nonstoichiometry was investigated and shown in this work. It has been observed that yttrium doping can affect the electrical properties of SrTiO3 to a great extent. Moreover, the microstructural and electrical properties can be influenced by strontium nonstoichiometry. The defect chemistry explaining obtained results was also suggested and discussed.

Structure changes in (Bi-Pb)-Sr-Ca-Cu-O glass ceramics during the first minutes of crystallization

Abstract (Bi 0.8 Pb 0.2 ) 4 Sr 3 Ca 3 Cu 4 O x glasses were prepared by a standard technique of quenching homogenised and melted substrates. The glass-ceramic samples were obtained by annealing of the glass at temperatures between 700 and 850 °C. The presence of crystalline phases was studied by X-ray diffraction analysis at room temperature and at the temperature of annealing. Superconducting phases e.g. (Bi 0.8 Pb 0.2 ) 2 Sr 2 Cu 1 O x , (Bi 0.8 Pb 0.2 ) 2 Sr 2 CaCu 2 O x , (Bi 0.8 Pb 0.2 ) 2 Sr 2 Ca 2 Cu 3 O x and other oxides like Cu 2 O and CaO were detected. Both scanning electron microscopy and XRD analysis show that during the first 30 min of crystallization the crystalline grains dimensions change from smaller than 0.1 μm to several μm.

Superconducting and anelastic effects in Pb-doped BiSrCaCuO ceramics

Abstract The resistivity, shielding and anelastic effects in Pb-doped Bi 2− x Pb x Sr 2 Ca 2 Cu 3 O y ceramics, where x = 0-0.6, have been studied. The best superconducting properties have been achieved for x = 0.4. The chemical analysis shows that the real Pb content is lower than the nominal. Energy dissipation spectra show no maximum around the transition temperature. A sharp peak at 215 K has been interpreted as being due to a first order antiferromagnetic transition.