A, B site doping strategy enhances Sr0.9Y0.1Fe1-xNixO3-δ structural stability, electrical and magnetic properties driven by Fe (Ⅳ) ions

Abstract

The SrFeO3-δ system attracts much attention due to its diverse crystal structures and favorable physicochemical properties. In this study, we introduced 10% Y ions into the Sr-site of oxygen-deficient metastable SrFeO3-δ, successfully synthesized a stable perovskite structure Sr0.9Y0.1FeO3-δ, though a tiny tetragonal phase SrFeO2.86 existed. Then, by gradient doping magnetic Ni ions at the Fe-site, the Sr0.9Y0.1Fe1-xNixO3-δ (x = 0.05~0.1) polycrystals were of a pure cubic perovskite structure with some lattice contraction, while x = 0.2, tiny traces of NiO (1.1%) are precipitated with slight lattice expansion. As x increased to 0.2, all samples were of p-type semiconducting transport in small polaron conduction and antiferromagnetic behavior (TN~66 → 58 K). The introduction of Ni2+/3+ drove grain growth and Fe3+ conversion to Fe4+ (Fe4+~50.39% → 70.62%) as well as oxygen vacancies increase. Resulting in thermal activation energy reduction (Ea~0.1135 → 0.0784 eV), and hole carrier concentration increase (n~9.69·1016 → 1.15·1019 cm-3), consequently room-temperature resistivity magnitude decrease (ρ_{300 K} ~48.08 → 0.65 Ω·cm). While the HS-Ni2+/3+ (t_2g⁶e_g², S = 1, t_2g⁵e_g², S = 3/2) partially replaces LS-Fe3+ (t_2g⁵e_g⁰, S = 1/2) and induced the LS-Fe3+ transform to HS-Fe4+ (t_2g³e_g¹, S = 2), which enhanced the effective magnetic moment of B-site ions (μeff~3.22 → 4.07 μB) and magnetization intensity (M_max, FC~52.71 → 135.8 10-3·emu/g).