Synthesis of CoxMn1−xO4 (0.9≤x≤2.7) Nanopowders with Controlled Phase and Composition Via a Gel-Combustion Method

CoxMn3−xO4 (CMO) nanopowders with a wide compositional range (0.9≤x≤2.7) are synthesized using a gel combustion method. The effect of Co content and calcination temperature on the crystal structure of the CMO nanopowders is studied using X-ray diffraction. A highly crystalline cubic spinel structure can be obtained at a relatively low temperature (~700°C) for CMO with a Co content of 1.8. Further increases in Co content to 2.7 leads to a higher formation temperature (~800°C) required in order to form a crystalline cubic structure. X-ray photoelectron spectroscopy revealed that the Co and Mn cations have mixed valence states. Energy dispersive X-ray elemental mapping indicates that Co and Mn cations are homogeneously distributed in the CMO nanopowders. Thermogravimetric analysis, Fourier transform infrared, scanning electron microscopy, and X-ray fluorescence are utilized to investigate the formation of the CMO nanopowders, as well as the compositional and structural properties.