Low Temperature Phase Transition in Lithium Manganese Oxide Spinel

Phase transition in lithium manganese oxide spinel compound at low temperature has been investigated. It is found that the cubic structure of LiMn2O4-δ with space group Fd-3m at room temperature was distorted to orthorhombic symmetry with space group Fddd at 290 K and become more obvious down to 10 K, where the splitting indicates the structural transition close to tetragonal. The equal proportion of coexisted Mn3+ (Jahn-Teller) and Mn4+ ions is associated with partial charge ordering. The extent of orthorhombic distortion is related to oxygen vacancy, , which is affected by synthesis method such as the choice of starting materials, mixing method and annealing temperature.