Oxygen diffusion mechanisms in two series of oxide ion conductors: BIMEVOX and Brownmillerite materialsReport as inadecuate




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1 UCCS - Unité de Catalyse et de Chimie du Solide

Abstract : They are two ways to optimize the electrical properties of a material, 1 tailor its microstructure, 2 tailor its structure by partial substitution. The BIMEVOX family, which was evidenced in the end of the eighties by members of our group, was obtained by partial substitution for vanadium in the parent compound Bi4V2O11 with a metal. This led to the stabilization of the highly conductive gamma Bi4V2O11 form at room temperature. BIMEVOX exhibit the best oxide ion conduction at moderate temperature, 400-700°C. However, because of the sensitivity of bismuth toward reduction, they could not be directly used in Solid Oxide Fuel Cells. We attempted to develop them as electrolyte for the electrically driven separation of oxygen from air and as membrane for the oxidation of hydrocarbons. Their high oxide conduction is due to their layered structure. Another family of oxide ion conductors with a bidimensionnal structure is the Brownmillerite. In 1990, Goodenough evidenced high oxide conduction in the Ba2In2O5 Brownmillerite above 925°C. In order to stabilize these high properties at lower temperature, numerous partial substitutions were performed on either the Ba or the In site. Our group considered the partial substitution for Indium with cation with valence higher than 3, such as Sn, V, Ta, Nb, Mo and W. Solid solutions were obtained for all the dopants. High temperature neutron diffraction was performed on the two family of oxide ion conductors. Because of the high oxide ion disorder, anharmonic thermal parameters were used to take into account all the nuclear density. Preferential oxygen pathways were derived, energy barriers were calculated and compared to the experimental values obtained from impedance spectroscopy. In a second step, their microstructure were optimized to obtain the dense ceramic needed for the applications. This was easily achieved for BIMEVOX but not for Brownmillerite which hydrate around 200-400°C and exhibit proton conduction in this domain of temperature.





Author: Aurélie Rolle - Pascal Roussel - Chanapa Kongmark - Caroline Pirovano - Rose-Noëlle Vannier -

Source: https://hal.archives-ouvertes.fr/



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