Structure and Electron Density Analysis of Lithium Manganese Oxides by Single-crystal X-ray Diffraction

Single crystals of LiMn 2 O 4 and LiMnO 2 have been successfully synthesized by a flux method. The lithium-ion deintercalated λ-MnO 2 single crystal has been prepared electrochemically using a microelectrode-based system. The single-crystal X-ray diffraction study at room temperature confirmed the cubic spinel F d 3 m space group for LiMn 2 O 4 and λ-MnO 2 , and the orthorhombic P m n m space group for LiMnO 2 , respectively. The crystal structure of LiMn 2 O 4 was refined using two models. A new oxygen displacement model with 1/3 occupation at the 96 g site gives better reliable values R =1.70% and w R =1.49% for 213 independent reflections. The crystal structure of LiMnO 2 has been refined to the reliable values R =1.32% and w R =1.45% for 676 independent reflections. In order to understand chemical bonding nature of these materials, we performed to analyze the electron density distributions by Maximum Entropy Method (MEM) using the single-crystal X-ray diffraction data. From the results of MEM analysis, the strong covalent bonding features were found between the Mn and O atoms in these manganese oxides. We also calculated electron density in LiMn 2 O 4 and LiMnO 2 by the full-potential linearized augmented-plane-wave (FLAPW) method. The electron density distribution features obtained theoretically were in good agreement with the experimental observations. A combined analysis of the MEM and FLAPW calculations clearly indicated that the covalent bonding observed between the Mn and O atoms in LiMn 2 O 4 is mainly assigned to the Mn-3d and O-2p hybridization which locates in the energy range of -7.5< E <-2.5 eV.