Phase equilibria in the system Pr+Co+O at 1100 and 11503C are established by changing the oxygen partial pressure from 0 to 12.00 in ؊log (P O 2 /atm), and a representative phase diagram at 11003C is presented for the Pr 2 O 3 +Co+CO 2 O 3 system. Under experimental conditions, the PrO 1.63؉ ( ), Pr 2 O 3 , CoO, Co, Pr 2 CoO 4 , Pr 4 Co 3 O 10 , and PrCoO 3 phases are present at both temperatures. The stoichiometric Pr 2 CoO 4 is not stable. The nonstoichiometry of the compounds, Pr 2 CoO 4 , Pr 4 Co 3 O 10 , and PrCoO 3 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 standard Gibbs energy changes of the reactions in the phase diagrams are calculated and their linearity with temperature is con5rmed under the present experimental conditions.
2000 Academic Press
The phase equilibrium in the Pr}Co}O system has been established at 12003C by author (1). It was clari"ed in the report that phases Pr O , Co, CoO, Pr CoO , Pr Co O , and PrCoO 3 are stable. Moreover, standard Gibbs energy changes of reactions were determined based on the phase diagram obtained, and lattice constants of Pr CoO , Pr
Co O , and PrCoO were determined using quenching samples. The structures and lattice parameters of these compounds, of course, were reported previously (2}5). The pattern of the system is di!erent from that of the La}Co}O system (6), which has the same La CoO , La Co O , and LaCoO type compounds. The objectives of the present study are also (1) to establish detailed phase equilibria in the system at 1100 and 11503C as a function of a oxygen partial pressure, (2) to determine the thermochemical properties based on the phase equilibria at di!erent temperatures, and (3) to ascertain whether the isothermal pattern of the phase diagram of the Pr}Co}O system at 1100 and 11503C changes for La}Co}O type at 12003C, in which stoichiometric Pr CoO is stable, with temperature or not.