This compound had an ABO3 perovskite structure and became non-stoichiometric upon changing the ratio of Sc3+ to Nb5+ ions. The stoichiometric material was an O ionic conductor, but became an excellent protonic conductor (activation energy: 0.63eV) after pre-treatment in water vapour. The protonic conductivity was shown to be proportional to the (lower-O) deviation from stoichiometry. This was characteristic of stage-II (unassociated) behavior. In the case of higher-than-stoichiometric O contents, the compound did not take up H and remained an O ionic conductor even though the O-vacancy concentration was suppressed in this case. There was no evidence of conduction via electronic defects or A- or B-site vacancies.

Effect of Non-Stoichiometry on the Protonic and Oxygen-Ionic Conductivity of Sr2(Sc,Nb)O6: a Complex Perovskite. A.S.Nowick, K.C.Liang: Solid State Ionics, 2000, 129[1-4], 201-7