Thermogravimetric study of the Ln(2)O(3)-Co-Co2O3 system .4. Ln=La at 1100 and 1150 degrees C

Phase equilibria in the system La-Co-O at 1100 and 1150 degrees C are established by changing the oxygen partial pressure from 0 to 12.00 in -log(PO2/atm), and a phase diagram of the La2O3-Co-Co2O3 system is represented. Under the experimental conditions, La2O3, CoO, Co, La2CoO4, LaCoO3, and La4Co3O10 phases are present. Nonstoichiometry of the compound is presented with respect to the oxygen partial pressure, and activities of the components in the solid solutions are calculated by using the composition-oxygen partial pressure relations obtained. The standard Gibbs energy changes of the reactions in the phase diagrams are calculated and their linearity with reciprocal temperature is confirmed under the present experimental conditions. (C) 1997 Academic Press.