Incorporation of Molecular Species into the Vacancies of Perovskite Oxides

Complex perovskites from the system Sr3Ca1(Zr(1-x)Ta(1+y))O8.5-x/2 offer a high concentration of oxygen vacancies and show promise as good proton conductors for SOFC and related applications. The oxygen-ion vacancies can be filled by O-H groups, by exposing the sample to a wet 5% H-2/Ar atmosphere at intermediate temperatures (350-400 degreesC). However, by using high temperatures (> 1000 degreesC) and/or pressures, we present evidence that molecular species such as carbonate and oxygen may be "forced" into this perovskite structure. Structurally, these would typically exist in a large part as CO32- species, with evidence for a small amount of superoxide (O-2(-)) formation from Electron Paramagnetic Resonance (EPR) results on oxygenated samples. Electron Spin Resonance studies suggest that some of the oxygen species exist as peroxidic groups coordinated to zirconium, giving rise to a sextet. The perovskite structure is retained throughout, although a number of modifications are linked to the loss of molecular species from the lattice. (C) 2002 Elsevier Science B.V All rights reserved.