High Temperature Thcrmodynamic Data of the Compounds in the La (Sr, Ca)- Mn-O System

摘要

The perovskite-type compounds based on doped and undoped lanthanum manganites form an important and interesting object of study owing to their technologically useful electric, magnetic and catalytic proporties. The thermodynamic properties of the lanthanum manganites are strongly affected by the partial substitution of La on A-site. In the present work the solid electrolyte galvanic cells method have been used in order to evidence new correlations existing between the composition and the thermodynamie properties of the following perovskite-type materials: La_(0.7)Sr_(0.3)MnO_3. La_(0.7)Ca_(0.3)MnO_3. The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen have been obtained in the temperature range of 1073-1273 K as a function of temperature and the dopant nature. The results are discussed being related with the variation of the predominant defects in the oxygen sublattice of the perovskite-type structure.