On the sol–gel synthesis and characterization of strontium ferrite ceramic material

Abstract 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 (SrFeO 3− ξ ; ξ ∼ 0.13) phase with a o = 3.862 ± 0.002 A, (ii) contains both the Fe 4+ and Fe 3+ species in 2.8:1 ratio, (iii) undergoes Fe 4+ → Fe 3+ reduction upon heating at 650 °C in rare gas ambient and transition to an orthorhombic phase with a ∼ a o √2, b ∼ 4 a o , c ∼ a o √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 °C.