Effect of an Excess of Lithium Ions on the Formation of Mn-Substituted LiFe₅O₈ with an Ordered Spinel Structure

Investigations on the series of manganese-substituted lithium ferrites revealed the destructive effects of Mn3+ ions on the ordering of Li+ cations in the resulting spinel crystal lattice. Considering fin-ther studies it appears, however, that the formation of Li-Mn-Fe oxides with ordered spinel structure is conditioned by the type of Mn-Fe precursors and the Li/(Fe+Mn) molar ratio. It was found that the LiFe5-yMnyO8 (0 less than or equal to y less than or equal to 1.5) solid solutions, obtained by heating at 750 degreesC in air the alpha-(Fe,Mn)(2)O-3 precursors with Li2CO3, display the spinel structures ordered (P4(3)32) for y = 0 - 1.0) and disordered (Fd3m) for y greater than or equal to1.25. The oxidation degree of manganese ions, in all precursors and in Li-Mn ferrites, was (+3) for the whole range of y. Distribution of cations in the A and B spinel sublattices was determined by X-ray powder diffraction techniques, including measurements of integrated intensities of single peaks and the Rietveld refinement. Evidence is given that the lithium ions occupy the octahedral sites exclusively, for the molar ratio 0 less than or equal to Mn/(Fe+Mn) less than or equal to 0.3.