Analysis of X-ray Absorption Spectra of Some Nickel Oxycompounds Using Theoretical Standards

Abstract

X-ray absorption spectra have been measured for NiO, β-Ni(OH)2, α-Ni(OH)2, LiNiO2, and KNiIO6 samples, which contain nickel with valency in the range 2−4. Information on the local structure and nature of bonding of nickel compounds has been derived using theoretical standards generated with the FEFF code. The Ni K-edge energy was found to shift to higher values by about 1.5 eV per unit change in valency of nickel. The energy of the preedge peak (generally attributed to the transition from the 1s core states to the 3d unoccupied states) shifts to higher values by about 0.6 eV per unit change in valency of nickel. A many body amplitude reduction factor ( ) of 0.77 ± 0.03 for Ni K-edge absorption can be used to scale theoretical spectra to fit the experimental ones in order to accurately determine the coordination numbers for compounds with complex structures. Our results show that chemical effects are very small and can be ignored for reliable structural analysis. Results of local structure for the first, s...