Co2o3

The raw material Co₂O_3, with a minimum purity of 99%, was purchased from Merck Company (Darmstadt, Germany).
To synthesize CoO, Co₂O₃ has been reduced in the extra pure hydrogen gas in a controlled atmosphere in the electrical tube-furnace operated between 180 °C and 500 °C for 1 h to choose the best temperature that results in “almost” pure CoO nanoparticles. The achieved product (CoO identified by XRD) is then used to synthesize Co-oxide/Co inverted core/shell nanostructures by reducing the extra pure hydrogen at 370 °C, utilizing the same furnace. The amount of hydrogen required to reduce 80% of Co-oxide is calculated based on the weight of the Co-oxide powder and estimated the particle and the crystallite sizes of the powder. Lastly, the obtained Co-oxide/Co nanostructures (Co-oxide /Co identified by XRD) are oxidized in the pure oxygen at 260 °C for different time intervals to obtain Co-oxide /Co/ Co-oxide core/shell/shell nanostructures with various shell thicknesses. All nanoparticles collected under the name OMO-series and are identified with their oxidation times: OMO(0), OMO(5), OMO(20), OMO(40), OMO(60), and OMO(80).

The RSrCoFeO₆ (R =
Sm, Eu) samples were prepared by using the solid-state
reaction process. First, the precursor oxides Sm₂O₃ (Alfa Aesar, 99.9% REO), Eu₂O₃ (Alfa
Aesar, 99.9% REO), SrCO₃ (Merck), Co₂O₃ (Merck, >99%), and Fe₂O₃ (Merck, >99%)
were
mixed in the proper stoichiometric ratio. Afterward, we placed the
mixture together with 20 zirconia balls (∼5 mm diameter) in
a Retsch PM100 planetary ball mill at 450 rpm for 30 min (dry without
a medium). Finally, the powder was thermally treated for 12 h at 1100
°C in an air atmosphere, thus obtaining the final compounds.