An electron hole doping and soft x-ray spectroscopy study on La1-xSrxFe0.75Ni0.25O3-{\delta}

The conductivity of the electron hole and polaron conductor La1-xSrxFe0.75Ni0.25O3-{\delta}, a potential cathode material for intermediate temperature solid oxide fuel cells, was studied for 0 <x < 1 and for temperatures 300 K <T < 1250 K. In LaSrFe-oxide, an ABO3 type perovskite, A-site substitu-tion of the trivalent La3+ by the divalent Sr2+ causes oxidation of Fe3+ towards Fe4+, which forms conducting electron holes. Here we have in addition a B-site substitution by Ni. The compound for x = 0.5 is identified as the one with the highest conductivity ({\sigma} ~ 678 S/cm) and lowest activation energy for polaron conductivity (Ep = 39 meV). The evolution of the electronic structure was monitored by soft x-ray Fe and oxygen K-edge spectroscopy. Homogeneous trend for the oxida-tion state of the Fe was observed. The variation of the ambient temperature conductivity and activation energy with relative Sr content (x) shows a correlation with the ratio of (eg/eg+t2g) in Fe L3 edge up to x=0.5. The hole doping process is reflected by an almost linear trend by the variation of the pre-peaks of the oxygen K-edge soft x-ray absorption spectra

Flame spray synthesis and characterisation of stabilised ZrO2 and CeO2 electrolyte nanopowders for SOFC applications at intermediate temperatures

Zirconia (Y0.16Zr0.84O2, Sc0.2Zr0.8O2 and Sc0.2Ce0.01Zr0.79O2) and ceria (Gd0.2Ce0.8O2) based electrolyte materials are synthesised at production rates up to 260g h−1 by a liquid-fed one-step flame spray synthesis from water-based solutions, or cost-effective rare earth nitrates with a high water content. It was found that this one-step synthesis, based on an acetylene-supported flame is able to produce phase pure and highly crystalline, nanoscale electrolyte materials. The as-synthesised powders show a cubic lattice structure independent of production rates. Specific surface areas of the powders were adjusted between 20 and 60m2 g−2, where the latter is an upper limit for the further processing of the powders in terms of screen printing. The influence of process parameters on morphology, particle size, composition, crystallinity, lattice parameter, shrinkage behaviour and coefficient of thermal expansion of the as-synthesised powders were systematically investigated by transmission electron microscopy (TEM), nitrogen adsorption (BET), X-ray diffraction (XRD) and dilatometry. Electrochemical impedance spectroscopy (EIS) was applied at temperatures between 300°C and 900°C and confirmed the high quality and the competitive electrochemical behaviour of the produced powder

A virus biosensor with single virus-particle sensitivity based on fluorescent vesicle labels and equilibrium fluctuation analysis

Biosensors allowing for the rapid and sensitive detection of viral pathogens in environmental or clinical samples are urgently needed to prevent disease outbreaks and spreading. We present a bioanalytical assay for the detection of whole viral particles with single virus sensitivity. Specifically, we focus on the detection of human norovirus, a highly infectious virus causing gastroenteritis. In our assay configuration, virus-like particles are captured onto a supported lipid bilayer containing a virus-specific glycolipid and detected after recognition by a glycolipid-containing fluorescent vesicle. Read-out is performed after illumination of the vesicle labels by total internal reflection fluorescence microscopy. This allows for visualization of individual vesicles and for recording of their binding kinetics under equilibrium conditions (equilibrium fluctuation analysis), as demonstrated previously. In this work we extend the concept and demonstrate that this simple assay setup can be used as a bioanalytical assay for the detection of virus particles at a limit of detection of 16 fM. Furthermore, we demonstrate how the analysis of the single vesicle-virus-like particle interaction dynamics can contribute to increase the accuracy and sensitivity of the assay by discriminating specific from non-specific binding events. This method is suggested to be generally applicable, provided that these events display different interaction kinetics

X-ray computed micro tomography as complementary method for the characterization of activated porous ceramic preforms

X-ray computed micro tomography (CT) is an alternative technique to the classical methods such as mercury intrusion (MIP) and gas pycnometry (HP) to obtain the porosity, pore-size distribution, and density of porous materials. Besides the advantage of being a nondestructive method, it gives not only bulk properties, but also spatially resolved information. In the present work, uniaxially pressed porous alumina performs activated by titanium were analyzed with both the classical techniques and CT. The benefits and disadvantages of the applied measurement techniques were pointed out and discussed. With the generated data, development was proposed for an infiltration model under ideal conditions for the production of metal matrix composites (MMC) by pressureless melt infiltration of porous ceramic preforms. Therefore, the reliability of the results, received from different investigation techniques, was proved statistically and stereologicall

Fe-resonant valence band photoemission and oxygen NEXAFS study on La1-xSrxFe0.75Ni0.25O3-{\delta}

Iron resonant valance band photoemission spectra of Sr substituted LaFe0.75Ni0.25 O3-{\delta} have been recorded across the Fe 2p - 3d absorption threshold to obtain Fe specific spectral information on the 3d projected partial density of states. Comparison with La1-xSrxFeO3 resonant VB PES literature data suggests that substitution of Fe by Ni forms electron holes which are mainly O 2p character. Substitution of La by Sr increases the hole concentration to an extent that the eg structure vanishes. The variation of the eg and t2g structures is paralleled by the changes in the electrical conductivity

Oxygen transport in La0.5Sr0.5Fe1−yTiyO3− δ ( y =0.0, 0.2) membranes

The influence of partial substitution of Fe with Ti on the oxygen transport properties of La1−x Sr x FeO3 membranes was investigated in view of their application for oxygen separation. Samples of composition $$La_{{0.5}} Sr_{{0.5}} {\text{Fe}}_{{1 - y}} {\text{Ti}}_{y} {\text{O}}_{{3 - \delta }}$$ (y=0, 0.2) were prepared and their oxygen transport properties characterised by potential step relaxation and by oxygen permeation measurement in an air/argon gradient. With the first technique, chemical diffusion $${( {\widetilde{D}} )}$$ and surface exchange (k S) coefficients were obtained by fitting of the current relaxation data to a single expression valid over the complete time range. The Ti-substituted composition gave slightly larger values of $${\widetilde{D}}$$ and k S. The trend was opposite for the measured oxygen permeation flux. In the latter experience, ordering of oxygen vacancies was observed at lower temperature, reducing significantly the performance of the materia

Mapeamento da gestão ambiental de uma das unidades do Centro de Artes (CeArte - UFPel): uma abordagem de membros do GIGA-UFPEL

A questão ambiental é uma preocupação global. A extração acentuada de recursos naturais não renováveis, a crescente quantidade de resíduos tóxicos e/ou resíduos não degradáveis acumulados, o consumo inconsciente, o desperdício, a poluição gerada por diversas situações, dentre outros, possibilitam alterações no planeta as quais são desfavoráveis a qualquer tipo de ser vivo. Porém, a atual forma de produção e comercialização é o que sustenta a população e o que supre suas necessidades diárias, mesmo, as supérfluas.Sem bols

Properties of B-site substituted La0.5Sr0.5FeO3−δ{\mathbf{La}}_{{0.5}} {\mathbf{Sr}}_{{0.5}} {\mathbf{FeO}}_{{3 - {\mathbf{\delta }}}} perovskites for application in oxygen separation membranes

Mixed ionic-electronic conducting $$La_{0.5} Sr_{0.5} Fe_{1 - x} B_x O_{3 - \delta }$$ (B: Al, Cr, Zr, Ga, Ti, Sn, Ta, V, Mg, and In with x = 0, 0.1, 0.2) perovskite materials were produced via solid-state synthesis. In order to study the effect of B-site substitution on the expansion behavior of these materials, their thermal expansion in air up to 900°C and isothermal expansion at the same temperature from air to Ar were measured by dilatometry. Ti and Ta were found to be the most effective substitutions in suppressing the isothermal expansion. The isothermal expansion at 900°C from air to Ar was reduced by 50% by substitution of 20% Ti or 10% Ta. Therefore, these compositions were further characterized by 4-probe total DC conductivity and permeation measurements under air/Ar gradient. The total conductivity of $$La_{0.5} Sr_{0.5} FeO_{3 - \delta }$$ was decreased by more than one order of magnitude at low temperatures and from 430S/cm, which is the maximum, to around 100S/cm at 500°C with the addition of Ti and Ta. The normalized oxygen permeation of LSF at 900°C decreased from 0.18 to 0.05μmol/cm2s and 0.07μmol/cm2s with the substitution of 20% Ti and 10% Ta, respectivel

Modeling the effect of molecular architecture of comb polymers on the behavior of Al2O3 dispersions using charge/composition factors (CCF)

Erworben im Rahmen der Schweizer Nationallizenzen (www.nationallizenzen.ch)In this work, we study the effect of periodicity and PEO side-chain length in four PMAA-PEO (sodium salt) comb polymers with known molecular architecture on Al2O3 colloidal dispersions in DI water. We introduce here charge composition factors (CCF) representing charge density of the comb polymers defined as (number of charged units in a repeating unit)/(molecular weight of a repeating unit). We find, for the first time to our knowledge, that the CCF can be used along with dispersant dosage to obtain explicit functions predicting the conductivity of the dispersants in solution, the zeta potential behavior during dispersant titrations, and the isoelectric point (IEP) of the dispersions. In addition, the dosage normalized by the CCF provides a basis for comparison for the dispersants to elucidate the trends found in adsorption and potentiometric titrations. Thus, the CCF can be used as a tool for the design of improved and new comb polymer molecular architectures

The effect of solvent and electric field on the size distribution of iron oxide microdots: Exploitation of self-assembly strategies for photoelectrodes

An increasing number of technologies benefit from or require patterned surfaces on a micro- and nanoscale. Methods developed to structure polymer films can be adapted to fabricate low-cost patterned ceramics using nonlithographic techniques, for example, dewetting and phase separation in thin films. In this paper we describe a simple patterning process that does not require a template and is able to produce Fe2O3 microdots with a spatial periodicity. Our method involves the dewetting of a silicon substrate by a thin metal oxide precursor film, in which the liquid film breaks up because of fluctuations in the film thickness induced by solvent evaporation or an external applied electric field. The patterning is followed by a thermal treatment at 550 °C to produce crystalline Fe2O3 microdots with a diameter range of 200 nm to 3 μ