Reduced forms of LaNiO3 perovskite. Part 1.—Evidence for new phases: La2Ni2O5 and LaNiO2

Abstract

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.