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

The SrCoO3-delta 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 SrCoO3-delta via Er doping to regulate the structural, electrical and magnetic transport properties. Sr1-xErxCoO3-delta (x = 0-0.25) undergoes an evolution of structure and oxygen content (measured using the iodometric method) from hexagonal SrCoO2.626 (H + Co3O4) to cubic perovskite Sr0.9Er0.1CoO2.689 (CP) and finally to ordered tetragonal Sr0.8Er0.2CoO2.635 (OT). Among the three phases, Sr0.9Er0.1CoO2.689 (CP) exhibits the lowest resistivity, only 4.06 m Omega 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, t(2g)(5)e(g)(0), S = 1/2) to high spin Co3+ (HS, t(2g)(4)e(g)(2), S = 2), and from the CoO6 octahedron (low magnetic moment transformation) to the CoO4.25 tetrahedron (high magnetic moment). The oxygen-deficient CoO4.25 layer appears, which can enhance the ordering of A sites and oxygen vacancies, and the CP phase transforms into room-temperature ferromagnetic Sr0.8Er0.2CoO2.635 (OT, T-C similar to 330 K). Er ions provide unpaired electrons in the 2f orbital, which results in a strong magnetization of Sr0.8Er0.2CoO2.635 (OT, 4.66 mu(B)/Co) at low temperatures.