STUDY ON THE DISPERSION OF NICKEL IONS IN THE NIO-MGO SYSTEM BY X-RAY-ABSORPTION FINE-STRUCTURE

NiO-MgO samples (NixMgl-xO:x = moles of Ni/(moles of Ni + moles of Mg) ) were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3)(2), followed by calcination at 773 K. The dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), X- ray photoelectron spectroscopy (XPS), and X-ray absorption fine struct ure (XAFS). XPS of the depth profile of the samples shows that the ato mic concentration of Ni and Mg against the depth is almost constant an d close to those of bulk concentrations. The analyses by EXAFS and XAN ES reveal the absence of the preferential segregation of nickel oxide phase or magnesium oxide phase in all samples, suggesting the substitu tion of Ni ions for Mg ions. A detailed analysis by the curve-fitting method indicates that Ni ions dissolving into MgO are dispersed at ran dom, regardless of the compositions of the samples. These results sugg est that these samples form solid solutions over the entire compositio n range, even by calcination at 773 K.