Charge ordering at low temperature in lithium manganese oxide spinel

Spinels lithium manganese oxide LiMn₂O_4-δ synthesized from mixtures of different raw materials were used to study the relationship between the synthesis method and properties of the spinel. The investigation was emphasized on phase transition in lithium manganese oxide spinel compound at low temperature studied by means of neutron powder diffraction. It is found that the cubic structure of LiMn₂O_4-δ, synthesized from Li₂CO₃, with space group Fd-3m at room temperature was distorted to orthorhombic symmetry with space group Fddd at 290K and become more obvious down to 10K, 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. It is also found that the sample synthesized from LiOH.H₂O and MnO_x does not show phase transition at low temperatures. The extent of orthorhombic distortion is related to oxygen vacancy, δ, which is affected by the synthesis method such as the choice of starting materials, mixing method and annealing temperature.