The oxygen flux through La1.9Sr0.1NiO4+delta has been measured as a function of oxygen activity gradient and temperature (750-1000 degrees C). The oxygen nonstoichiometry was determined by thermogravimetry in the temperature range of 400-1000 degrees C and oxygen partial pressures of 0.0002-1 atm. The total conductivity was measured over a similar range of conditions. The oxide ion partial conductivity derived from the oxygen flux data is approximately 4 orders of magnitude lower than the total, mainly p-type electronic conductivity. The defect structure was derived based on the data. Combining the oxygen flux and oxygen nonstoichiometry, the self diffusion coefficient of oxygen interstitials was evaluated. (C) 2009 Elsevier B.V. All rights reserved.