Introducing gradient Er ions and oxygen defects into SrCoO 3 for regulating structural, electrical and magnetic transport properties.

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- δ via Er doping to regulate the structural, electrical and magnetic transport properties. Sr 1- x Er x CoO 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 + Co 3 O 4 ) to cubic perovskite Sr 0.9 Er 0.1 CoO 2.689 (CP) and finally to ordered tetragonal Sr 0.8 Er 0.2 CoO 2.635 (OT). Among the three phases, Sr 0.9 Er 0.1 CoO 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 Co 4+ (LS, t52ge0g, S = 1/2) to high spin Co 3+ (HS, t42ge2g, S = 2), and from the CoO 6 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 0.8 Er 0.2 CoO 2.635 (OT, T C ∼330 K). Er ions provide unpaired electrons in the 2f orbital, which results in a strong magnetization of Sr 0.8 Er 0.2 CoO 2.635 (OT, 4.66 μ B /Co) at low temperatures.