Spinel Solid Solutions in the Li–Fe–Mn–O System

The ranges of Li–Fe–Mn composition in which single-phase microparticulate spinel oxides are formed by heating in air were determined. The aim was to reevaluate previously published reports on binary solid solutions between LiFe5O8 and Li–Mn–O spinels by covering the whole possible range of (Li,Fe,Mn)3O4 spinels with Mn valence higher than 3. To sensitively detect possible heterogeneity of the elemental distribution or phase composition, chemical and X-ray powder diffraction analyses were used, temperature dependence of magnetic susceptibility was obtained for samples rich in Fe, and electrochemical reductive dissolution was studied by means of voltammetry of microparticles. Instead of a continuous series of solid solutions, three regions were found with different dependence of lattice parameters on elemental composition. A region of nonuniform solid solutions was found at Fe/(Fe+Mn)>0.4 and Mn valence >3.2.