Structural and thermal properties of LiMn2O4 substituted for manganese by iron

Structural and thermal properties of Fe-doped lithium manganese oxides, Li0.9Mn2−xFexO4 and LiMn2−xFexO4, were studied by means of X-ray diffraction (XRD), Mössbauer spectroscopy, DSC and TGA methods. Mössbauer spectroscopy measurements revealed that the iron in Fe-doped samples existed as high spin Fe3+ (main component) and Fe4+ (minor component) in noncubic octahedral site (16d). Lattice constants of Fe-doped samples increased with increasing doped iron contents, probably due to the substitution of Fe4+ with large ionic radius for Mn4+ with small ionic radius. Disappearance of endothermic peak due to Jahn–Teller effect of Mn3+ and Fe4+ around room temperature for Li0.9Mn2−xFexO4 with higher iron contents reflects mainly the substitution of Fe3+ for Mn3+. Starting temperature of weight loss for LiMn2−xFexO4 determined by TGA measurements increased with increasing iron contents and weight loss at constant temperature decreased. Doped iron of the samples seems to play an important role in the thermal stability of the spinel structure at high and low temperatures.