The role of Cu doped Ba_0.5Sr_0.5Fe_0.95Zr_0.05O_3-δ: Local structure distortion, conductivity, and magnetization

The composition Ba_0.5Sr_0.5Fe_1-xCu_xZr_0.05O_3-δ (BSFCZ-x, x = 0–0.20) was successfully synthesized by the sol-gel self-combustion method using citric acid as fuel combustion. Structure, local structure, electrical, and magnetic properties are investigated. The X-ray diffraction revealed the oxides exhibit a cubic structure (Pm3 m), and the lattice parameter increases with x. The X-ray absorption data are analyzed to determine the oxidation state of B site metal transition Fe and Cu through edge-energy E₀ evaluation. Fe performs the oxidation states Fe3+ and Fe4+, similarly to Cu²⁺ and Cu³⁺. Furthermore, the pre-edge was analyzed to determine the spin state configuration of the 3d subshell. The local lattice distortion was evaluated through EXAFS, resulting in a distorted FeO₆ octahedron elongated to the z-axis, inducing the Jahn-Teller effect. The nonstoichiometric δ-value (3-δ) measurement leads to oxygen vacancy V_O^⦁⦁ defect. The electrical conductivity of semiconducting behavior increases significantly after Cu is dissolved in BSFZ up to 60 S/cm at 500 °C, from initially 5 S/cm. Furthermore, the magnetic properties show a slight magnetic saturation Ms for BSFZ related to the low spin state configuration of Fe 3d subshell, then significantly increased on BSFCZ samples due to Cu provoking spin state dragged partly to high spin state configuration.