Structural and optical absorption studies of barium substituted strontium ferrite powder

Abstract

Attempt has been made to synthesize BaxSr1−xFeO3−ξ (x = 0–1.0) ferrite powder by decomposition of sol–gel derived oxalate at 800–1000 °C for 5–10 h to study the effect of barium insertion with regard to phase(s), stability, optical behavior, oxidation states of iron, and oxygen deficiency. It is shown that these ferrites possess a perovskite-type cubic phase (a = 3.877–4.020Å, Z = 1, space group Pm3m) for 0.1 ≤ x ≤ 0.94, a mixture of 82% rhombohedral (aR = 5.666Å and αR = 59.761°, Z = 2, space group R3c) and 18% hexagonal phases for x = 0.96 and a pure hexagonal (a = 5.689Å, c = 13.944Å, Z = 6, space group P63/mmc) phase for x = 1. Barium substitution in SrFeO3−ξ system leads to lattice expansion, weakening of the metal-oxygen bond, reduction of tetravalent iron ions (as evident from Mossbauer analysis), and decrease of oxygen content. The optical absorption peaks observed in the range 3.17–4.11 eV are attributed to charge transfer transitions from O2− (2p) to Fe (3d) band. The values of optical energy band gap of BaxSr1−xFeO3−ξ are found to be ∼5.48 and ∼4.04 for x = 0.1 and 1.0, respectively. A stable perovskite-type cubic phase in BaxSr1−xFeO3−ξ system with significant anion deficiency (ξ = 0.26–0.32) may possibly act as an oxygen permeable membrane.