XAS Study on Oxygenated LaSrNiO4 and La2NiO4+δ

XANES studies at Ni K-edge have been performed for LaSrNiO3.99, and La2NiO4+δ treated under various atmosphere conditions as well as chemical and electrochemical oxidation methods. XRD patterns of polycrystalline have shown a well crystallized single phase, and valence states of Ni were carefully determined by iodometric titration, resulting in δ=0.01-0.17. The oxidation from Ni(II) to Ni(III) is indicated by an absorption edge shift to higher energy side, which is in good agreement with the amount of excess oxygen determined by iodometric titration. XANES study suggests that the doped holes in nickelates are more localized on nickel sites than those in cuprate