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The perovskite-type cubic oxides have found useful applications in catalysis, solid oxide fuel cells, gas sensors, and membrane technology. XPS and Raman studies of a recently developed (Ba0.5Sr0.5)(Al0.2-xMgxFe0.8)O3-ξ (x = 0–0.2) oxygen-permeable system are reported here. The effect of magnesium is shown to alter the relative amounts of Fe3+, Fe4+, and oxygen species via Fe (2p3/2 and 2p1/2) and O 1s signals. Besides, it causes a surge in oxygen vacancies, an increase in Fe3+ ions, a decline in B – O bond strength (B = Al/Mg/Fe), and a rise in anion flow. The O1s signals at ~ 528.5 and ~531.0 eV correspond to surface oxide and adsorbed (O22−, O2−, or O−) species, respectively. Raman spectra offer evidence for symmetric A1g stretching, oxygen vacancies, distorted BO6 octahedra, A-O stretching vibration modes (A = Ba, Sr), and bending B-O linkages. A good correlation is advanced between the XPS and Raman results, in conformity with lattice expansion, Mossbauer data, improved oxygen permeability, enhanced electrical conductivity, and high structural stability realized by means of partial replacement of Al3+ with Mg2+ in (Ba0.5Sr0.5)(Al0.2Fe0.8)O3-ξ earlier.