Sol-gel synthesis, crystalline phase, optical absorption, and photo-luminescence behavior of cerium-doped (Ba0.5Sr0.5)FeO3-δ powders

Abstract

The cerium- and iron-based perovskite type materials have received attention due to their applications in solid oxide fuel cells, sensors, catalysts, and gas separation membranes. An attempt has been made here to synthesize (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0-1.0) compounds and characterize them for crystalline phases, photoluminescence and optical absorption properties. They are shown to exhibit phases as perovskite-type cubic for x = 0, cubic as well as orthorhombic in the composition range 0.1 ≤ x ≤ 0.6 and orthorhombic alone for 0.8 ≤ x ≤ 1.0. The lattice parameter of cubic phase increases with cerium content, value being ∼3.937 Å and 3.981 Å for x = 0 and 0.60, respectively with Z = 1 and space group Pm3m. The orthorhombic cell has ao = 8.871 Å, bo = 6.392 Å, co = 5.991 Å, Z = 4 and space group Pnma for the composition x = 1.0. Cerium insertion leads to lattice expansion, weakening of metal-oxygen bonds, creation of oxygen vacancies, M4+ → M3+ (M = Ce and/or Fe) conversion, and creation of defect levels within the band gap. Their photoluminescence spectra provide evidence for structural defects including oxygen vacancies. The optical absorption peaks at 620 and 700 nm are attributed to various charge transfer transitions. The characteristics make the (Ba0.5Sr0.5)(Fe1-xCex)O3-δ system technological viable for oxygen separation from air. © 2019 IOP Publishing Ltd.