A defect and transport model was described for acceptor-doped La2-xSrxNiO4+δ with the layered K2NiF4 structure. The model included mobile O interstitials in the rocksalt layers and O vacancies in the perovskite layers of the crystal structure. Based upon fits to published data concerning the deviation from stoichiometry, defect concentrations were calculated for La1.5Sr0.5NiO4+δ as a function of PO2 at 1073 to 1223K. Application of the transport model to the present O permeation data clearly indicated that the O transport in La1.5Sr0.5NiO4+δ was governed mainly by the migration of mobile O interstitials. According to the model calculations, a significant contribution of vacancy migration to O permeation was to be expected only for O partial pressures lower than 10−5 bar at 1223K, and at even lower partial pressures at 1073 and 1173K. Permeation data were not available for such low partial pressures, and O migration via vacancies could not be confirmed, nor ruled out.

Oxygen Transport in La2-xSrxNiO4+δ - Membrane Permeation and Defect Chemical Modelling. M.Schroeder, M.A.Dragan: Journal of Materials Science, 2007, 42[6], 1972-83