THERMODYNAMIC STUDY OF THE NDO3-CO-CO2O3 AND ODO3-CO-CO2O3 SYSTEM .2.

Phase equilibria in the system Ln//2O//3-Co-Co//2O//3 (Ln equals Nd and Gd) at 1200 degree C were studied at oxygen partial pressures ranging from 1 to 10** minus **1**2 atm O//2. NdCoO//3 and Nd//4Co//3O//1//0 are stable ternary compounds in the Nd//2O//3-Co-Co//2O//3 system, while only GdCoO//3 is stable in the Gd//2O//3-Co-Co//2O//3 system. Nd//4 Co//3O//1//0 was found to be a new compound; its lattice constants have been determined from data on La//4Co//3O//1//0. The standard Gibbs energies of the reactions appearing in the systems were also determined from the oxygen partial pressures in equilibrium with three solids. The variation of DELTA G degree with the ionic radius of Ln with 12 coordination is linear.