Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba4Ca2Ta2O11 have been investigated. Ba4Ca2Ta2O11 crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H2O per mol Ba4Ca2Ta2O11. In moist air, the structure symmetry becomes monoclinic (C2/m) 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 EA = 0.85 eV. In the intermediate temperature range (400–600 °C), O2− anionic and protonic conductions are mixed with an activation energy EA = 0.45 eV and in the third region, for temperatures above 600 °C, O2−conduction is prevailing with an activation energy EA = 0.85 eV.

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