Reduced forms of LaNiO3 perovskite. Part 1.—Evidence for new phases: La2Ni2O5 and LaNiO2
Low-temperature reduction of LaNiO3 under hydrogen leads to new compounds such as La2Ni2O5 and LaNiO2 before total reduction. Hydrogen consumption, X-ray diffraction and XANES demonstrate the presence of these new phases. Ni3+ in LaNiO3 becomes Ni2+ in La2Ni2O5, and a pure monovalent nickel phase is obtained in LaNiO2. After this stage nickel leaves the structure as nickel metal. Before total reduction, reversible reoxidation of La2Ni2O5 and LaNiO2 leads to the original structure of the LaNiO3 perovskite.