K2NiF4-type perovsldte oxides LaSrIn1-xBxO4+delta (B = Zr, Ti) were synthesized and characterized in order to identify its capability of incorporating interstitial oxygen atoms (delta) and their effect on the crystal structure and oxide-ion conduction. The synthesis has been performed by a citrate-nitrate soft-chemistry technique followed by annealings in air at moderate temperatures (1000 degrees C). The samples have been characterized at room temperature from x-ray diffraction (XRD) and the structure has been analyzed from neutron powder diffraction (NPD) data in the Pbca space group. Interstitial oxygen atoms were identified by difference Fourier maps in the NaCl layer of the K2NiF4 structure; subsequent Rietveld refinements yield excess oxygen values, delta = 0.048(4) and 0.079(5) for B = Zr with x = 0.1 and 02, respectively, and delta = 0.049(5) for B = Ti,x = 0.1. The performance of each oxide as a potential oxide ion conductor was evaluated by ac impedance spectroscopy using Pt as electrodes and compared with the parent compound LaSrInO4. The lowest activation energy and better ion conductivity were observed for LaSrIn0.8Zr0.2O4+0.08, which is consistent with the highest amount of interstitial oxygen found from NPD data. (C) 2015 Elsevier B.V. All rights reserved.