CHARACTERIZATION OF OXYGEN-DEFICIENT PEROVSKITES AS OXIDE-ION ELECTROLYTES

Oxide-ion conduction in oxygen-deficient perovskites is analogous in several respects to that in oxygen-deficient fluorite structures. We report here an important difference: oxygen-deficient AMO3-y perovskites containing M cations that are unstable in less than sixfold anion coordination may, at modest temperatures, capture oxygen and/or water from air to fill, at least partially, the oxygen vacancies. The insertion of water introduces mobile protons; the insertion of oxygen oxidizes the oxide-ion array in the presence of fully oxidized main group cations. We illustrate this insertion with the perovskite system BaZr1-xInxO3-0.5x, M = Zr or Hf. The data suggest that any ordering of the oxygen vacancies so as to give planes of comer-shared MO4 tetrahedra permits facile insertion of water and/or oxygen. In contrast, the oxygen-deficient fluorite structure has each cation in at least sixfold oxide-ion coordination, and the problem of water or oxygen insertion at modest temperatures does not arise.