Oxygen K-edge XANES investigation of Ni_cMg_{1 - c}O solid solutions

A series of Ni_cMg_{1 - c}O solid solutions are characterized by means of synchrotron radiation X-ray diffraction and X-ray absorption near-edge-structure spectroscopy at oxygen K-edge (532 eV). A dramatic drop of the pre-edge peak intensity is observed in the Ni_cMg_{1 - c}O system upon dilution. It can be attributed to a decrease of 3d⁸(Ni²⁺)-2p(O^2-) mixing upon dilution with magnesium ions due to a decrease of the number of 3d vacancies as nickel ion is replaced by magnesium ion. Similarly, the decrease of the number of 4s and 4p vacancies also leads to a decrease of 4s4p(Ni²⁺)-2p(O^2-) hybridization, and hence a drop of intensities of features B and C. The features E and F are more sensitive to the increase of the degree of disorder upon dilution than feature D, revealing that the latter is mainly dependent by the medium-range order.