Electron density distribution of LiMn 2 O 4 by the single-crystal diffraction study

Lithium manganese spinels are attractive candidates for cathode materials of rechargeable lithium ion batteries. Stoichiometric LiMn2O4 is a mixed valence compound comprised of distinct Mn(III) and Mn(IV) ions in equal proportions. Above the transition temperature Tc, Mn(III) and Mn(IV) ions are randomly distributed amongst the 16d sites of Fd-3m symmetry, while they are localized on five independent sites in Fddd symmetry below Tc. The lithium ion dynamics, which is very important from a viewpoint of practical applications, is also different in the high (HT) and low temperature (LT) phases. Structural information about these two phases is therefore essential for understanding of the processes involved. Powder Xray and neutron diffraction experiments have been reported previously by other authors but high precision single crystal X-ray diffraction experiments in principle can provide more accurate three dimensional information about the electron density. Here we report on the LT structure determined via single-crystal synchrotron X-ray diffraction.