Data on O permeation through dense samples of La2-xSrxNi1-y-zFeyCuzO4-δ (x = 0 to 0.10, y = 0.02 to 0.10, z = 0 to 0.10), LaPrNi0.9Fe0.1O4+δ, La2Cu1-xCoxO4+δ (x = 0.02 to 0.30) and Ln2CuO4+δ (Ln = Pr or Nd) at 973 to 1223K suggested that there were 2 significant contributions to the ionic conductivity of the O-hyperstoichiometric phases. The relative importance of the first of these (O interstitial migration in the rocksalt-type layers of the K2NiF4-like lattice) increased with increasing temperature. The importance of O vacancy diffusion in the perovskite layers increased with decreasing temperature. This was attributed to the lower activation energy for ionic conduction via the vacancy diffusion mechanism. The O permeability of the materials was found to be limited by both the bulk ionic conductivity and by surface exchange rates, and might be enhanced by catalytically active layers which were deposited on the membrane surface. The O permeability of the K2NiF4-type phases which exhibited the greatest ionic transport (such as La2Ni0.98Fe0.02O4+δ, La2Ni0.88Fe0.02Cu0.1O4+δ and La2Cu0.90Co0.10O4+δ) was about an order of magnitude lower than that of most permeable perovskite-type materials. Decreasing radii of the rare-earth cations in the A sub-lattice of the cuprates and nickelates led to a marked decrease in ionic transport.

Ionic Transport in Oxygen-Hyperstoichiometric Phases with a K2NiF4-Type Structure. V.V.Kharton, A.P.Viskup, A.V.Kovalevsky, E.N.Naumovich, F.M.B.Marques: Solid State Ionics, 2001, 143[3-4], 337-53