Effective tuning of electromagnetic properties in Sr0.9Y0.1FeO3−δ ceramics via high valence and spin-state Mn doping at the B-site

Abstract

The perovskite SrFeO_3−δ system features a highly tunable structure, offering high potential for performance regulation and application. Cubic perovskite Sr_0.9Y_0.1Fe_1−xMn_xO_3−δ (x = 0–0.6) ceramics with A-site Y doping and B-site Mn^3+/4+ doping were synthesized by a solid-state reaction method. When x = 0–0.4, the ceramics exhibit a single-phase structure with lattice contraction, due to the substitution of Fe^3+/4+ by smaller Mn^3+/4+ ions with a higher average valence, which also induces Jahn–Teller distortion along the c-axis of the MnO₆ octahedra and reduces the crystal symmetry. When x = 0.6, a trace secondary phase of SrMnO₃ appears. Donor doping of Mn leads to the reduction of Fe⁴⁺ to Fe³⁺ (Fe³⁺% = 50.86–61.98%) and a decrease in oxygen vacancies, reducing the intrinsic hole carrier concentration. The thermal activation energy E_a for small-polaron conduction increases (0.1135–0.1308 eV), resulting in a significant increase in resistivity. Meanwhile, it is suggested that the enhancement of Mn³⁺–O–Mn⁴⁺ double-exchange interactions and the weakening of Fe⁴⁺–O–Fe⁴⁺ super-exchange interactions lead to a decrease in Néel temperature T_N (64–22 K) and a weakening of exchange bias. The introduction of HS-Mn^3+/4+ (t_2g³e_g¹/S = 2, t_2g³e_g/S = 3/2) promotes the partial transformation of HS-Fe⁴⁺ (t_2g³e_g¹, S = 2) into LS-Fe³⁺ (t_2g⁵e_g⁰, S = 1/2). The increase in the effective magnetic moment of B-site ions contributes to an enhancement in magnetization.