Structural, magnetic, electrical and electrochemical properties of SrCoO_2.5, Sr₉Co₂Mn₅O₂₁ and SrMnO₃ compounds

SrCo_1−xMn_xO_3−d (0 ≤ x ≤ 1) were synthesized by conventional solid state reaction method. We found that Mn substitution hinders the decomposition of carbonate at 900 °C and increases the synthesis temperature of SrCo_1−xMn_xO_3−d to 1200 °C. Three different main phases emerge as the Mn content is increased; SrCoO_2.5, Sr₉Co₂Mn₅O₂₁ and SrMnO_3. Structural properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy (SEM). Valance states of the transition metal (TM) ions were estimated based on lattice parameters and ionic radii of TM ions. High temperature resistivity measurements show hysteresis upon heating and cooling and is attributed to oxygen release without any endothermic/exothermic activity. The spin configurations of Co and Mn ions in SrCoO_2.5, Sr₉Co₂Mn₅O₂₁ and SrMnO₃ were estimated by Curie-Weiss fitting of χ-T curves. Electrochemical measurements show two anodic/cathodic peaks indicating two main types of oxygen sites in the unit cell.