998 resultados para Sr^2


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<p>Ni-substituted Sr<sub>2</sub>Fe<sub>1.5-x</sub>Ni<sub>x</sub>Mo<sub>0.5</sub>O<sub>6-</sub> (SFNM) materials have been investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Reduced samples (x = 0.05 and 0.1) maintained the initial perovskite structure after reduction in H<sub>2</sub>, while metallic nickel particles were detected on the grain surface for x = 0.2 and 0.3 using transmission electron microscopy. Temperature programmed reduction results indicate that the stable temperature for SFNM samples under reduction conditions decreases with Ni content. In addition, X-ray photoelectron spectroscopy analysis suggests that the incorporation of Ni affects the conductivity of SFNM through changing the ratios of Fe<sup>3+</sup>/Fe<sup>2+</sup> and Mo<sup>6+</sup>/Mo<sup>5+</sup>. Sr<sub>2</sub>Fe<sub>1.4</sub>Ni<sub>0.1</sub>Mo<sub>0.5</sub>O<sub>6-</sub> shows the highest electrical conductivity of 20.6 S cm<sup>-1</sup> at 800 C in H<sub>2</sub>. The performance of this anode was further tested with electrolyte-supported cells, giving 380 mW cm<sup>-2</sup> at 750 C in H<sub>2</sub>, hence demonstrating that Ni doping in the B-site is beneficial for Sr<sub>2</sub>Fe<sub>1.5</sub>Mo<sub>0.5</sub>O<sub>6-</sub> anode performance.</p>

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<p>In this paper strontium-site-deficient Sr<sub>2</sub>Fe<sub>1.4</sub>Co<sub>0.1</sub>Mo<sub>0.5</sub>O<sub>6-</sub>-based perovskite oxides (S<sub>x</sub>FCM) were prepared and evaluated as the cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). All samples exhibited a cubic phase structure and the lattice shrinked with increasing the Sr-deficiency as shown in XRD patterns. XPS results determined that the transition elements (Co/Fe/Mo) in S<sub>x</sub>FCM oxides were in a mixed valence state, demonstrating the small polaron hopping conductivity mechanism existed. Among the samples, S<sub>1.950</sub>FCM presented the lowest coefficient of thermal expansion of 15.62 10<sup>-6</sup> K<sup>-1</sup>, the highest conductivity value of 28 S cm<sup>-1</sup> at 500 C, and the lowest interfacial polarization resistance of 0.093 cm<sup>2</sup> at 800 C, respectively. Furthermore, an anode-supported single cell with a S<sub>1.950</sub>FCM cathode was prepared, demonstrating a maximum power density of 1.16 W cm<sup>-2</sup> at 800 C by using wet H<sub>2</sub> (3% H<sub>2</sub>O) as the fuel and ambient air as the oxidant. These results indicate that the introduction of Sr-deficiency can dramatically improve the electrochemical performance of Sr<sub>2</sub>Fe<sub>1.4</sub>Co<sub>0.1</sub>Mo<sub>0.5</sub>O<sub>6-</sub>, showing great promise as a novel cathode candidate material for IT-SOFCs.</p>

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<p>In this paper, Sr<sub>2</sub>Fe<sub>1.5</sub>Mo<sub>0.4</sub>Nb<sub>0.1</sub>O<sub>6-</sub> (SFMNb)-xSm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>2-</sub> (SDC) (x = 0, 20, 30, 40, 50 wt%) composite cathode materials were synthesized by a one-pot combustion method to improve the electrochemical performance of SFMNb cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The fabrication of composite cathodes by adding SDC to SFMNb is conducive to providing extended electrochemical reaction zones for oxygen reduction reactions (ORR). X-ray diffraction (XRD) demonstrates that SFMNb is chemically compatible with SDC electrolytes at temperature up to 1100 C. Scanning electron microscope (SEM) indicates that the SFMNb-SDC composite cathodes have a porous network nanostructure as well as the single phase SFMNb. The conductivity and thermal expansion coefficient of the composite cathodes decrease with the increased content of SDC, while the electrochemical impedance spectra (EIS) exhibits that SFMNb-40SDC composite cathode has optimal electrochemical performance with low polarization resistance (R<sub>p</sub>) on the La<sub>0.9</sub>Sr<sub>0.1</sub>Ga<sub>0.8</sub>Mg<sub>0.2</sub>O<sub>3</sub> electrolyte. The R<sub>p</sub> of the SFMNb-40SDC composite cathode is about 0.047 cm<sup>2</sup> at 800 C in air. A single cell with SFMNb-40SDC cathode also displays favorable discharge performance, whose maximum power density is 1.22 W cm<sup>-2</sup> at 800 C. All results indicate that SFMNb-40SDC composite material is a promising cathode candidate for IT-SOFCs.</p>

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SR , , , 2 m&times; 5 m; 4 , 4 , 2 m&times; 2 0 m , , ,

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A capillary electrophoresis method coupled with electrochemiluminescence detection for the analysis of quinolizidine alkaloids was established, especially, oxymatrine (OMT) which could not be measured by previous electrochemiluminescence methods was detected sensitively herein. Complete separation of sophoridine (SR), matrine (MT) and OMT was achieved within 13 min using a background electrolyte of 50mM phosphate buffer at pH 8.4 and a separation voltage of 15 kV. The calibration curves showed a linear range from 2.8 x 10(-8) to 4.4 x 10(-7) M for SR, 2.7 x 10(-8) to 4.4 x 10(-7) M for MT.

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(Endoplasmic reticulum , ER ) (Sarcoplasmic reticulum , SR) (2 300 m ) (5 000m 7 000m )24 h , 5 000 m ER Ca2+ , 7 000 m ER Ca2+29102%7 d SR Ca2+ER Ca2+5 000 m 7 000 m 32.50% 33.33%25 d ER , SR Ca2+ .: Ca2+, 7 d , 25 d

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Recent measurements on the resistivity of (La-Sr)(2)CuO4 are shown to tit within the general framework of Luttinger liquid transport theory. They exhibit a crossover from the spin-charge separated ''holon nondrag regime'' usually observed, with rho(ab) similar to T, to a ''localizing'' regime dominated by impurity scattering at low temperature. The proportionality of rho(c) and rho(ab) and the giant anisotropy follow directly from the theory.

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A detailed study of the layered manganite La1+xSr2-xMn2O7 has been performed, establishing that within the composition range 0.1 less than or equal to x less than or equal to 0.45 the phases crystallize in the I4/mmm space group. The evolution of structural parameters with x: in this composition range has been followed using a novel application of an existing program for the Rietveld analysis of powder diffraction data. The structure, a familiar intergrowth of rock-salt (La,Sr)O slabs and double perovskite (La,Sr)(2)Mn2O6 units, is characterized by a reluctance to deform the latter. This manifests as a ''pumping'' of the larger Sr-II ion into the 12-coordinate site of the structure as x is increased. We report these features of the structure as well as electrical transport and magnetic properties, in light of recent observations of giant, negative magnetoresistance in these systems.