Local structure analysis of BO6 (B = Fe, Cu) octahedron correlated with the magnetic properties of Cu-doped Ba0.5Sr0.5FeO3–δ

Perovskite-based Ba0.5Sr0.5Fe1–xCuxO3–δ (BSFCO-x, x = 0–0.2) was synthesized by sol–gel self-combustion method. The crystallinity was evaluated through X-ray diffraction, besides further local structure analysis, using X-ray absorption spectroscopy (XAS) showed a cubic symmetry for x = 0.05; 0.10, which was tetragonal at higher values, x = 0.15; 0.20. XAS analysis predicted the oxidation state (OS) of Cu to be a mixture of 3+ and 2+, while Fe includes 3+ and 4+. Conversely, the OS of Fe and Cu in the octahedron site influence the number of an unpair electron that determine the magnetic properties of perovskite. In addition, the magnetization for Ba0.5Sr0.5FeO3–δ is 0.172 emu g−1, originating from the ferromagnetic ordering Fe3+(t 2g 3 e g 2 )–O (2p)–Fe4+(t 2g 3 e g 1 ) interaction. This effect increase, due to the presence of oxygen vacancy in BSFCO-0.05, which weakens the d–p interaction of Fe-O, while the generation of higher Cu doping to increase the amount of Fe4+ leads to a decline in Cu3+. Therefore, Cu doping is confirmed to play a role in the paramagnetic–ferromagnetic transition.