On the X-ray photoelectron spectra, oxygen permeability, and electrical conductivity variations in (Ba0.5Sr0.5)(ZnηFe1-η)O3-ξ (η=0, 0.2) system

The perovskite ABO(3-xi) cubic compounds have received attention due to their widespread applications in sensors, oxygen pumps, and gas separation. An attempt has been made here to study the X-ray photoelectron spectra, electrical conductivity, and oxygen permeability of sol-gel-derived (Ba0.5Sr0.5)(Zn eta Fe1-eta)O3-xi (eta = 0 and 0.2) compounds. Zinc insertion is shown to (i) retain the perovskite-type cubic phase-increasing the lattice parameter from 3.937 to 3.975 +/- 0.002 angstrom, (ii) limit (xi) value within 0.2-0.6, (iii) lower the conductivity, and (iv) reduce the oxygen permeability but provide structural stability. Further, XPS data reveal decrease in Fe4+ species more than Fe3+ ions, rise in anion vacancies, and differences in three types of oxygen ions (belonging to stoichiometric, oxygen-deficient, and surface regions) with binding energies in the range similar to 531.1 to 534.2 eV. Their discs serve as reliable oxygen-permeable membranes, exhibit flux density (J(O2)) of similar to 1.24 to 2.45 ml cm(-2) min(-1) at 1000 degrees C, and so found suitable for extracting pure oxygen from air.