EXAFS Study of Cation Distribution in Nickel Aluminate Ferrites

A new method for analyzing the cation distribution of spinel crystals by extended X-ray absorption fine-structure spectroscopy has been developed to overcome the disadvantage of X-ray diffraction, which cannot readily distinguish among different transition-metal ions. EXAFS analysis was conducted on Ni²⁺ and Fe³⁺ ions in nickel aluminate ferrites, and the cation distributions obtained were in good agreement with values obtained by other methods. The ratio of tetrahedral sites occupied by Ni²⁺ ions decreases with increasing iron content. Fe³⁺ ions distribute nearly equally to both tetrahedral and octahedral sites. Apparently, not only crystal-field stabilization energy but also ion size affects cation distribution.