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 beta-NiOOH is +3; Ni3O2(OH)4 and commercial nickel peroxide (NiO2) likewise contain trivalent nickel. The edge shift for quadrivalent nickel in KNilO6 is reported for the first time.