Differential scanning calorimetry -: An essential tool to characterize LiMn2O4 spinel

A series of LiMr2O4 samples with nominal Li/Mn molar ratio=1/2 has been synthesized at 700 and 750°C by the ceramic procedure from Mn2O3 and several lithium sources. Lattice parameters determined from X-ray diffraction patterns are within a narrow range, from ac=8.238(1) A to ac=8.245(1) Å, Δa c/ac<0.1%. The study by differential scanning calorimetry (DSC) shows that the temperatures of the cubic (Fd3m)↔orthorhombic (Fddd) phase transition are spread off in a wide range, from -30 to -2°C for the exothermic C→O phase transition, and from -21 to +13°C for the endothermic O→C transformation. Relationships between the lattice parameter values, the temperature of the phase transformation, and the stoichiometry of the LiMn2O4 samples are pointed out. The DSC technique, which reveals more sensitive than X-ray diffraction to very small variations of composition, is put forward as an essential technique to characterize LMn2O4 samples.