Effect of non-stoichiometry on the protonic and oxygen-ionic conductivity of Sr-2(ScNb)O-6: a complex perovskite

The compound Sr-2(Sc1+xNb1-x)O6-x has the ABO(3) perovskite structure. It b ecomes non-stoichiometric by changing the ratio of Sc3+ to Nb5+ ions, i.e. by varying x. For x > 0, this compound is an oxygen ionic conductor, but it becomes an excellent protonic conductor, with activation energy 0.63 eV, a fter pretreatment in water vapor. The protonic conductivity is shown to var y proportionately to x, characteristic of Stage II (unassociated) behavior. In the case of samples with x less than or equal to 0, the compound does n ot take up hydrogen, and, in fact, remains an oxygen ionic conductor even t hough the oxygen-vacancy concentration is suppressed in the case of negativ e x. There is no evidence for conduction by electronic defects or by A- or B-site vacancies. (C) 2000 Elsevier Science B.V. All rights reserved.