Abstract: The structure and the permeability of La₂NiO_4+δ oxygen permeating membranes were discussed. TEM studies of La₂NiO_4+δ show that La₂NiO_4+δ
contains a large amount of interstitial oxygen and exhibits a superstructure behavior owing to long range ordering of interstitial oxygen. The oxygen permeation
flux through La₂NiO_4+δ was determined and the relationship between mechanism of oxygen permeability and structure was discussed. The results indicate
that the oxygen transportation by interstitial mechanism is easier than that by vacancy mechanism.

Key words: La₂NiO_4+δ, oxygen permeating membrane, crystalline structure, mixed conductivity, oxygen permeability