Synthesis, structure, and phase relationship in lithium manganese oxide spinel

Abstract

Phase relationships, structures, magnetic properties, and phase transitions in the lithium manganese oxide spinel were studied based on a wide variety of samples synthesized at temperatures over a range of 750 ≤ t ≤ 900 °C with Li/Mn ratios between 0.5 and 0.55 and various starting materials. The system was divided into three categories: oxygen deficient spinels, LiMn₂O_4−δ; lithium-substituted spinels, Li_1+xMn_2−xO_4−δ; and the stoichiometric spinel, LiMn₂O₄. Their structures were discussed based on the structure data determined by TOF neutron and synchrotron X-ray Rietveld analysis. The amount of oxygen vacancy was determined to be δ ≈ 0.14(3) in LiMn₂O_4−δ, for example, for the spinel synthesized at 900 °C, and the nearly stoichiometric composition was obtained at 750 °C followed by heating at 470 °C for several times from lithium hydroxide and manganese oxides as starting materials. The oxygen vacancy was dependent upon the synthesis conditions and starting materials. It decreased as the Li/Mn ratio varied from 0.5 to 0.55, and as the synthesis temperature decreased from 900 to 750 °C. Based on the synthesis and structure results, the phase relationship in the ternary diagram, Li–Mn–O, is discussed.