Abstract
We describe a defect and transport model for acceptor doped \({\hbox{La}_{2-x}\hbox{Sr}_{x}\hbox{NiO}_{4+\delta}}\) with the layered K2NiF4 structure. The model includes mobile oxygen interstitials in the rocksalt layers and oxygen vacancies in the perovskite layers of the crystal structure. Based on fits of literature data of the deviation from stoichiometry, defect concentrations have been calculated for La1.5Sr0.5NiO4+δ as a function of p(O2) for 1,073–1,223 K. Application of the transport model to oxygen permeation data obtained in this work clearly indicates that the oxygen transport in La1.5Sr0.5NiO4+δ is primarily governed by migration of mobile oxygen interstitials. According to the model calculations, a significant contribution of vacancy migration to the oxygen permeation process is to be expected only for oxygen partial pressures lower than 10−5 bar at 1,223 K and even lower partial pressures at 1,073 and 1,173 K. As yet, permeation data are not available for such low partial pressures, which is why oxygen migration via vacancies could neither be confirmed nor ruled out.
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