Structure Refinement of Li₄Mn₅O₁₂with Neutron and X-Ray Powder Diffraction Data

Well-crystallized Li₄Mn₅O₁₂powder was prepared by heating a eutectic mixture of lithium acetate LiOAc and manganese nitrate Mn(NO₃)₂in an O₂atmosphere. The structure of Li₄Mn₅O₁₂crystallites was found to be cubic spinel using Rietveld refinement of both neutron and X-ray powder diffraction profiles. We confirmed that lithium ions occupy both the tetrahedral sites 8aand part of the octahedral sites 16d, but not the 16csites in the space groupFd3m, while all the manganese ions occupy the 16dsites. The lattice parameter was found to be sensitive to synthesis temperature as a result of the variation in manganese valence. The presence of Mn³⁺leads to the formation of a stoichiometric spinel Li[Li_xMn_2-x]O₄in whichxdecreases from 1/3 (Li₄Mn₅O₁₂) to 0 (LiMn₂O₄), with concomitant formation of Li₂MnO₃depending on the synthesis conditions.