Wyniki wyszukiwania - BazTech

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Structure and electrical properties of oxide-ion conductors in the Bi3NbO7-Bi3YO6 system

Kozanecka-Szmigiel A., Krok F., Abrahams I., Wrobel W., Chan S.C.M., Dygas J.R.

Materials Science Poland

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2006

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Vol. 24, No. 1

31--37

EN

A study of the structure and electrical conductivity of Bi3Nb1-xYxO7-x is presented. X-ray diffraction confirms full solid solution formation in this system, with the adoption of a fluorite-type structure. Superlattice ordering of the anion sublattice is evident in neutron diffraction data, the nature of which varies with composition. At low values of x, long-range ordering is present, whereas above x = 0.4 only local ordering is observed. Arrhenius plots of the total electrical conductivity of all samples containing yttrium show two linear regions with different activation energies, with evidence for a phase transition between 450 and 680 °C.

2

Oxide-ion conductors for fuel cells

Krok F., Abrahams I., Wrobel W., Kozanecka-Szmigiel A., Dygas J.R.

Materials Science Poland

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2006

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Vol. 24, No. 1

13--22

EN

The principal materials used in the construction of solid oxide fuel cells (SOFCs) are discussed. Some of the problems encountered with high temperature fuel cells (HT-SOFCs) might be overcome by lowering the operating temperature to 500-700 °C, through the development of suitable materials for intermediate temperature fuel cells IT-SOFCs. Candidate electrolyte materials are discussed, including cerium gallium oxide, lanthanum strontium gallium magnesium oxide, and electrolytes based on doped bismuth oxide. While high ionic conductivities can readily be achieved in these materials at intermediate temperatures, stability in reducing atmosphere is still a problem. This might be overcome by careful chemical design of electrolytes containing stabilising dopants. Two zirconia-doped bismuthate systems are discussed in this respect. In both cases, the obtained materials exhibit different structures - one is Bi3Nb1-xZrxO7-x/2 of the ?-Bi2O3 type, and the other, Bi4V2-2xZrxO11-x, has a layered structure of the Aurivillius type.

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Ionic conductivity of polymer electrolytes comprising acrylonitrile-butyl acrylate copolymer and a lithium salt

Łasińska A., Dygas J.R., Krok F., Marzantowicz M., Florjańczyk Z., Tomaszewska A., Zygadło-Monikowska E.

Materials Science Poland

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2006

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Vol. 24, No. 1

187--194

EN

New polymer electrolytes were prepared by mixing random copolymers of acrylonitrile and butyl acrylate (poly(AN-co-BuA)) with lithium bis(trifluoromethanesulfone) imide (LiTFSI). Electrical properties were studied by the impedance spectroscopy. The glass transition temperature was studied by DSC. Presented results concern a broad range of compositions, from a pristine copolymer to the system with 98 wt. % of salt. Correlation was established between the glass transition temperature, ionic conductivity, and salt content in the system. Mixtures of poly(AN-co-BuA) and LiTFSI exhibit much lower glass transition temperatures than the parent copolymer. Effects of ageing were observed for electrolytes with high salt content.

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In-situ study of the influence of crystallization on the ionic conductivity of polymer electrolytes

Marzantowicz M., Dygas J.R., Krok F., Zygadło-Monikowska E., Florjańczyk Z.

Materials Science Poland

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2006

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Vol. 24, No. 1

195--203

EN

Simultaneous impedance measurements and optical observations of polymer electrolytes were conducted in an automated experimental setup, combining an impedance analyser, polarizing microscope with a heating stage and a digital camera. The polymer film was placed between glasses with indium tin oxide conductive layers, forming a transparent cell mounted in a custom-designed holder, which preserved an argon atmosphere. Results of in-situ studies for various compositions of poly(ethylene oxide) (PEO) with LiN(CF3SO2)2 salt (LiTFSI), as well as pure PEO, are presented. In the investigated systems, crystallization had a strong impact on ionic conductivity. It was found that the initial growth of crystalline structures caused only a small fraction of the total decrease of conductivity. A large decrease in conductivity was observed during the second stage of crystallization, when no significant changes in microscope picture were observed. In pure PEO and the PEO:LiTFSI 6:1 system, a dense crystalline structure developed, resulting in a decrease in conductivity of over two orders of magnitude. In dilute PEO:LiTFSI systems, a "loose" structure was formed, with amorphous areas preserved between crystallites, and conductivity decreased by only a factor of about 6.

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Bi8V2O17 - a stable phase in the Bi2O3-V2O5 system

Wrobel W., Krok F., Abrahams I., Kozanecka-Szmigiel A., Malys M., Chan S.C.M., Dygas J.R.

Materials Science Poland

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2006

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Vol. 24, No. 1

23--30

EN

Bi8V2O17 is commonly observed as an intermediate phase in the synthesis of compounds in ternary systems of the type Bi2O3-V2O5-MexOy. It is also seen as an end product at particular compositions in these systems. A rhombohedral substructure model for this phase is presented along with electrical parameters. Evidence from the Arrhenius plot suggests a phase transition at around 550 °C. The existence of a limited solid solution of Bi8V2O17 with ZrO2 is also discussed.