Structural disorder along the lithium diffusion pathway in cubically stabilized lithium manganese spinel II. Molecular dynamics calculation

Molecular dynamics (MD) simulations were carried out to investigate the local structural disorder in LiMn₂O₄ spinel. Small but significant shifts of lithium and oxygen atom positions from the high symmetry sites of the Fd3̄m lattice were observed. The lithium atoms are displaced approximately 0.16Å away from 8a site of the Fd3̄m lattice and are shifted along the diffusion pathway towards the face midpoints of the coordinating LiO₄ tetrahedra. A diffuse population of Li atoms was also detected centered about 0.38Å away from the 16c octahedral vacancy, suggesting a portion of the Li atoms are free from their tetrahedral cages at room temperature. The tetrahedrally coordinated O atoms are displaced by as much as 0.12Å when bonded to one Li and three Mn atoms in identical oxidation states. On the other hand, if the coordinating Mn atoms are in mixed oxidation states, much larger O atom shifts of 0.22Å are observed. Structural features obtained in this MD simulation, especially the off-center displacements of Li and O atoms, are in accord with the electron density distribution study of cubically stabilized Mg-doped LiMn₂O₄ spinel reported in Part I.