Phase equilibria in the Fe-Nb-O system at 12000C

Phase equilibria in the system Fe-Nb-O at 12000C are established by changing the oxygen partial pressure from 0 to -15.00 in log (P/sub O2//atm) and are represented in the Nb2O5-Fe-Fe2O3 system. In this system, FeNbO4, FeNb2O6, Fe4Nb2O9, niobium-iron spinel, and NbO2 phases appear and have non-stoichiometric compositions. Lattice constants of the compounds and the solid solutions are determined and discussed with respect to the oxygen partial pressure dependency and to the coexistence of the other compounds. The lattice constant of the spinel solid solution increases with the increasing of the content of Fe7Nb2O12. The standard Gibbs energies of the reactions appearing in the phase diagram are calculated