Introducing gradient Er ions and oxygen defects into SrCoO3 for regulating structural, electrical and magnetic transport properties

Abstract

The SrCoO_3−δ system has broad application potential due to its diverse crystal structures, oxidation stoichiometric ratio, and significant electrical and magnetic properties. However, it faces the challenges of a complex crystal structure and oxygen defect control in this material system. Herein, we introduce oxygen defects into SrCoO_3−δvia Er doping to regulate the structural, electrical and magnetic transport properties. Sr_1−xEr_xCoO_3−δ (x = 0–0.25) undergoes an evolution of structure and oxygen content (measured using the iodometric method) from hexagonal SrCoO_2.626 (H + Co₃O₄) to cubic perovskite Sr_0.9Er_0.1CoO_2.689 (CP) and finally to ordered tetragonal Sr_0.8Er_0.2CoO_2.635 (OT). Among the three phases, Sr_0.9Er_0.1CoO_2.689 (CP) exhibits the lowest resistivity, only 4.06 mΩ cm at room temperature, which is attributed to its high three-dimensional symmetry, overlap of O 2p and Co 3d orbitals at high oxygen ion concentration. Further introduction of Er ions and oxygen defects promotes the transformation from low spin Co⁴⁺ (LS, t⁵_2ge⁰_g, S = 1/2) to high spin Co³⁺ (HS, t⁴_2ge²_g, S = 2), and from the CoO₆ octahedron (low magnetic moment transformation) to the CoO_4.25 tetrahedron (high magnetic moment). The oxygen-deficient CoO_4.25 layer appears, which can enhance the ordering of A sites and oxygen vacancies, and the CP phase transforms into room-temperature ferromagnetic Sr_0.8Er_0.2CoO_2.635 (OT, T_C∼330 K). Er ions provide unpaired electrons in the 2f orbital, which results in a strong magnetization of Sr_0.8Er_0.2CoO_2.635 (OT, 4.66 μ_B/Co) at low temperatures.