X-ray photoelectron spectra, conductivity, and oxygen permeation characteristics of (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) perovskites

Abstract

X-ray photoelectron spectra, conductivity and oxygen permeability of perovskite-type (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) oxides are reported. The concentration of Fe4+ and Ce4+ decreases with ‘x’ via Fe4+(/Ce4+) → Fe3+(/Ce3+) conversions which, in turn, oxygen deficiency (δ) increases. The spectrum of oxygen (O1s) is attributed to stoichiometric, adsorbed and chemically adsorbed species at ∼531.5, 532.8 and 534.4 eV, respectively (say, for x = 0.30). The oxygen permeability (Jo2) of disc membrane lies in the range of ∼1.474–2.204 ml/cm2-min at 950 °C (input feed air ∼400 ml/min, carrier argon gas ∼40 ml/min) for x = 0–1.0. Maximum Jo2 is observed for x = 0 (cubic phase) in comparison to other compositions viz., x = 0.10–0.60 (cubic + orthorhombic phases) and x = 0.80–1.0 (orthorhombic phase). The electrical conductivity increases until a characteristic temperature, then slowly decreases with increasing cerium concentration (x). The structural transformation of (Ba0.5Sr0.5)(Fe1-xCex)O3-δ plays an important role in determining the conductivity (σ) and oxygen permeation. These analyses make material useful for applications dealing with oxygen separations.