High-Temperature Oxygen Release from Complex Oxide La₂NiO_{4 + δ} in Quasi-Equilibrium Mode

A continuous quasi-equilibrium phase diagram δ(pO₂, T) of a nonstoichiometric oxide La₂NiO_{4 + δ} with the layered perovskite-like Ruddlesden–Popper structure is obtained by the method of quasi-equilibrium oxygen release. The thermodynamic parameters are determined as a function of the oxide nonstoichiometry δ. Calculations are carried out within the framework of the localized-electron and itinerant-electron models which are used for description of the defect structure of ferrites and cobaltites, respectively. It is shown that the specific features of the phase diagram can be related to the electronic density of states near the Fermi level.