OXYGEN NONSTOICHIOMETRY OF SPINEL LIMN2O4-DELTA

Oxygen nonstoichiometry delta has been determined for a spinel LiMn2O4 -delta sample as a function of oxygen partial pressure P-O2 in the tem perature range between 873 and 1123 K, using a thermogravimetric analy sis and a chemical titration analysis. The maximum oxygen deficiency o f LiMn2O4-delta was found to be delta(cr) similar to 0.2. For the samp les obtained at 1023 K, as delta increased from zero, the tetragonal s pinel phase appeared around delta = 0.07, while only the cubic spinel phase was observed for the samples with delta less than or equal to 0. 07. Partial molar enthalpy <Delta H(O2)over bar> and entropy <Delta S( O2)over bar> of oxygen in the LiMn2O4-delta samples with 0.05 less tha n or equal to delta less than or equal to 0.2 were estimated to be -20 8 to -277 kJ mol(-1) and -168 to -219 J K-1 mol(-1) respectively. The dependence of delta on P-O2 was expressed as delta similar to p(O2)((- 0.67+/-0.06)) to explain this relation, we employed a defect cluster m odel. In contrast, the sample with delta = 0.67 was found to decompose to LiMnO2 and Mn3O4. The change in standard enthalpy for the decompos ition Delta H-0 was estimated to be 84 kJ mol(-1).