A simple oxalate based sol-gel process has been described to produce a highly stable anion deficient strontium ferrite for separation of oxygen from air. The method involves metal nitrates and oxalic acid precursors with ethanol and water as solvents, gel formation, digestion for 4 h, drying at 150 C for 24 h, and finally decomposition at 800 C in air. The resulting material (i) exhibits a single perovskite-type cubic (SrFeO3-xi; xi similar to 0.13) phase with a(o) = 3.862 +/- 0.002 angstrom, (ii) contains both the Fe4+ and Fe3+ species in 2.8:1 ratio, (iii) undergoes Fe4+ -> Fe3+ reduction upon heating at 650 C in rare gas ambient and transition to an orthorhombic phase with a similar to a(o)root 2, b similar to 4a(o), c similar to a(o)root 2, which reverts back to cubic phase with oxygen uptake at elevated temperatures, and (iv) acts as filter for air with excellent oxygen permeation, typical flux density value being 2.45 ml/cm(2) min at 1000 degrees C. (C) 2012 Elsevier Ltd. All rights reserved.