Local structure analysis of BO₆ (B = Fe, Cu) octahedron correlated with the magnetic properties of Cu-doped Ba_0.5Sr_0.5FeO_3–δ

Perovskite-based Ba_0.5Sr_0.5Fe_1–xCu_xO_3–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 Ba_0.5Sr_0.5FeO_3–δ is 0.172 emu g⁻¹, originating from the ferromagnetic ordering Fe³⁺(t_2g³e_g²)–O (2p)–Fe⁴⁺(t_2g³e_g¹) 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.