Manganese sesquioxide to trimanganese tetroxide hierarchical hollow nanostructures: effect of gadolinium on structural, thermal, optical and magnetic properties

Abstract

Various hollow manganese oxide (bixbyite Mn₂O₃ and hausmannite Mn₃O₄) nanoparticles (NPs) with different morphologies were obtained from a single precursor, manganese oxalate (MnC₂O₄). To synthesize a Mn₃O₄ stacked nanostructure rather than coral-like Mn₂O₃ nanospheres, as synthesized MnC₂O₄ was thermally decomposed at 700 °C in the presence of Gd³⁺, through the oriented arrangement mechanism. The formation process and structural variation arising from varying the thermal treatment (450 °C and 700 °C) and the cationic dopant Gd³⁺ were analyzed by FTIR, TGA, and XRD. The unexpected size reduction, and significant physicochemical properties were analyzed using various techniques such as FESEM coupled with EDAX, HR-TEM, DRS-UV-vis, EPR, EIS and VSM. The addition of gadolinium induces particle size reduction and a phase transition from cubic Mn₂O₃ to tetragonal Mn₃O₄, which leads to the suppression of the electrical conductivity, and changes in the optical band gap. The prepared Mn₃O₄ nanocrystals exhibit ferromagnetic behavior below T_c ≈ 45 K and weak paramagnetic behavior at room temperature.