Complex perovskites from the system Sr3Ca(Zr(1-x)Ta(1+y))O8.5-x/2 offer a high concentration of O vacancies and showed promise as good proton conductors for SOFC and related applications. The O-ion vacancies could be filled by O–H groups, by exposing the sample to a wet 5%H2/Ar atmosphere at 350 to 400C. However, by using temperatures above 1000C, and/or pressures, evidence was found that molecular species such as carbonate and O could 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 (O2-) formation from electron paramagnetic resonance results on oxygenated samples. Electron spin resonance studies suggested that some of the O species existed as peroxide groups coordinated to Zr, giving rise to a sextet. The perovskite structure was retained throughout, although a number of modifications were linked to the loss of molecular species from the lattice.

Incorporation of Molecular Species into the Vacancies of Perovskite Oxides. J.T.S.Irvine, D.J.D.Corcoran, A.Lashtabeg, J.C.Walton: Solid State Ionics, 2002, 154-155, 447-53