Incorporation of water in strontium tantalates with perovskite-related structure

The electrical properties and water uptake of the oxygen-deficient perovski te-related compounds Sr6Ta2O11 and Sr5.92Ta2.08O11.12 have been investigate d with AC conductivity, transport number measurements and thermogravimetry. In wet atmospheres, they become hydrated mainly around 500 degreesC and ex hibit mixed proton and oxygen ion conductivity. Part of the water uptake to ward the theoretical hydration limit takes place in a step, probably a phas e transition related to oxygen vacancy disordering or proton ordering, or b oth. The transition is accompanied also by steps and maxima in total conduc tivity, believed again to be related to order-disorder reactions. (C) 2001 Elsevier Science B.V. All rights reserved.