Preparation and crystal structure refinement of Li₄Mn₅O₁₂ by the rietveld method

Well-crystallized Li₄Mn₅O₁₂ powder has been prepared by heating a eutectic mixture of lithium acetate LiOAc and manganese nitrate Mn(NO₃)₂ at 700°C for 1-3 days in an O₂ atmosphere. The Li and Mn content in the final products was determined from atomic absorption spectroscopy. The tetravalent manganese in the final product was found to be 95% based on the active oxygen content determined by KMnO₄ titration. The structure of Li₄Mn₅O₁₂ crystallites was refined by the Rietveld method from powder X-ray diffraction data as a cubic spinel, a = 8.1616(5) Å, space group Fd3̄m. Li₄Mn₅O₁₂ crystallites are stable at temperatures up to 600°C in oxygen but decompose to spinel LiMn₂O₄ and monoclinic Li₂MnO₃ at temperatures higher than 530°C in N₂.