Structure refinement of Li4Mn5O12 with neutron and X-ray powder diffraction data

Well-crystallized Li4Mn5O12 powder was prepared by heating a eutectic mixture of lithium acetate LiOAc and manganese nitrate Mn(NO3)(2) in an O-2 atmosphere, The structure of Li4Mn5O12 crystallites 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 8a and part of the octahedral sites 16d, but not the 16c sites in the space group Fd (3) over bar m, while all the manganese ions occupy the 16d sites, 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[LixMn2-x]O-4 in which x decreases from 1/3 (Li4Mn5O12) to 0 (LiMn2O4), with concomitant formation of Li2MnO3 depending on the synthesis conditions. (C) 1997 Academic Press.