Thermodynamic representation of nonstoichiometric lanthanum manganite

The thermodynamic properties of the lanthanum manganites, La_1-xMn_1-yO_3-z, have been reevaluated within the ideal association model to simultaneously account for excess oxygen and lanthanum nonstoichiometry of LaMnO_3+δ, La_0.95MnO_3+δ and La_0.9MnO_3+δ. It has been found that a new set of parameters can reproduce the essential features of the thermogravimetric results reported in literature; that is, the averaged manganese valence at P(O₂) = 1 atm does not depend largely on the lanthanum nonstoichiometry between LaMnO_3+δ and La_0.9MnO_3+δ. Beyond this composition, however, the thermodynamic model has predicted that the averaged manganese valence increases with decreasing lanthanum stoichiometry and has confirmed the key idea for explaining the chemical reactivity of the lanthanum manganite such as the La₂Zr₂O₇ formation and the Mn₃O₄ precipitation.