Thermogravimetric study of the Ln2O3-Co-Co2O3 system -: V.: Ln = Nd at 1100 and 1150°C

Phase equilibria in the system Nd-Co-O at 1110 and 1150 degrees C are established by changing the oxygen partial pressure from 0 to 12.00 in - log(P-o2/atm) and phase diagrams are presented for the Nd2O3-Co-Co2O3 system. Under the experimental conditions, Nd2O3, CoO, Co, Nd4Co3O10, and NdCoO3 phases are present at both temperatures. The nonstoichiometry of the compounds Nd4Co3O10 and NdCoO3 is represented with respect to the oxygen partial pressure, and activities of the components in the solid solutions are calculated using the composition-oxygen partial pressure relations obtained. The changes of the standard Gibbs energies of the reactions in the phase diagrams are calculated and their linearity with temperature is confirmed under the present experimental conditions. The relationship between the change of the standard Gibbs energy of a reaction and the ionic radius of the lanthanoid element is discussed. (C) 1998 Academic Press.