A, B site doping strategy enhances the structural stability as well as electrical and magnetic properties of Sr0.9Y0.1Fe1−xNixO3−δ driven by Fe(iv) ions

Abstract

The SrFeO_3−δ system has attracted much attention owing 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 SrFeO_3−δ and successfully synthesized a stable perovskite structure Sr_0.9Y_0.1FeO_3−δ; however, a trace amount of tetragonal phase SrFeO_2.86 existed. Then, by gradient doping magnetic Ni ions at the Fe site, Sr_0.9Y_0.1Fe_1−xNi_xO_3−δ (x = 0.05–0.1) polycrystals were found to exhibit a pure cubic perovskite structure with some lattice contraction, while for x = 0.2, small traces of NiO (1.1%) were precipitated with slight lattice expansion. As x increased to 0.2, all samples demonstrated p-type semiconducting transport in small polaron conduction with antiferromagnetic behavior (T_N = 66–58 K). The introduction of Ni^2+/3+ drove the grain growth and Fe³⁺ conversion into Fe⁴⁺ (Fe⁴⁺ = 50.39–70.62%) and an increase in oxygen vacancies, resulting in thermal activation energy reduction (E_a = 0.1135–0.0784 eV) and increase in hole carrier concentration (n = 9.69 × 10¹⁶–1.15 × 10¹⁹ cm⁻³), consequently decreasing room-temperature resistivity magnitude (ρ_300k = 48.08–0.65 Ω cm). Meanwhile, HS-Ni^2+/3+ (t_2g⁶e_g², S = 1; t_2g⁵e_g², S = 3/2) partially replaced LS-Fe³⁺ (t_2g⁵e_g⁰, S = 1/2) and induced the transformation of LS-Fe³⁺ to HS-Fe⁴⁺ (t_2g³e_g¹, S = 2), which enhanced the effective magnetic moment of B-site ions (μ_eff = 3.22–4.07μ_B) and magnetization intensity (M_max,FC = 52.71–135.8 × 10⁻³ emu g⁻¹).