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) angstrom, 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 degrees C, the protonic conduction is prevailing with an activation energy E-A = 0.85 eV. In the intermediate temperature range (400-600 degrees C). O2- anionic and protonic conductions are mixed with an activation energy E-A = 0.45 eV and in the third region, for temperatures above 600 degrees C, O2- conduction is prevailing with an activation energy E-A = 0.85 eV. (C) 2009 Elsevier Masson SAS. All rights reserved.