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en
Article de revue
Ce document a été publié dans
Solid State Sciences. 2009, vol. 11, n° 9, p. 1572-1575
Elsevier
Résumé en anglais
The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba<sub>4</sub>Ca<sub>2</sub>Ta<sub>2</sub>O<sub>11</sub> have been investigated. Ba<sub>4</sub>Ca<sub>2</sub>Ta<sub>2</sub>O<s ...Lire la suite >
The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba<sub>4</sub>Ca<sub>2</sub>Ta<sub>2</sub>O<sub>11</sub> have been investigated. Ba<sub>4</sub>Ca<sub>2</sub>Ta<sub>2</sub>O<sub>11</sub> crystallizes in the cryolite structure (cubic, <i>Fm</i>3<i>m</i> SG) with <i>a</i> = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H<sub>2</sub>O per mol Ba<sub>4</sub>Ca<sub>2</sub>Ta<sub>2</sub>O<sub>11</sub>. In moist air, the structure symmetry becomes monoclinic (<i>C</i>2/<i>m</i>) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy <i>E</i><sub>A</sub> = 0.85 eV. In the intermediate temperature range (400–600 °C), O<sup>2−</sup> anionic and protonic conductions are mixed with an activation energy <i>E</i><sub>A</sub> = 0.45 eV and in the third region, for temperatures above 600 °C, O<sup>2−</sup>conduction is prevailing with an activation energy <i>E</i><sub>A</sub> = 0.85 eV.< Réduire
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