X‐Ray Absorption Fine Structure Spectra and the Oxidation State of Nickel in Some of Its Oxycompounds

XANES spectra of nickel K‐edge and x‐ray diffraction patterns of several nickel oxycompounds were measured. The shift in energy of the Ni K‐absorption edge toward higher values correlates well with the increase in the oxidation state of nickel from +2 to +4 in the compounds studied. The inflection point energy of the Ni pre‐edge structure shifts approximately 1 eV per unit change in valency. Our results provide evidence which supports the assignment that the valency of Ni in is +3; and commercial nickel peroxide likewise contain trivalent nickel. The edge shift for quadrivalent nickel in is reported for the first time.