Copper ferrite, belonging to the wide and technologically relevant class of spinel ferrites, was grown in the form of t-CuFe₂O₄ nanocrystals within a porous matrix of silica in the form of either an aerogel or a xerogel, and compared to a bulk sample. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed the presence of two different sub-lattices within the crystal structure of t-CuFe₂O₄, one tetragonal and one cubic, defined by the Cu²⁺ and Fe³⁺ ions respectively. Our investigation provides evidence that the Jahn-Teller distortion, which occurs on the Cu²⁺ ions located in octahedral sites, does not affect the coordination geometry of the Fe³⁺ ions, regardless of their location in octahedral or tetrahedral sites.

The structural properties of zinc ferrite nanoparticles with spinel structure dispersed in a highly porous SiO₂ aerogel matrix were compared with a bulk zinc ferrite sample. In particular, the details of the cation distribution between the octahedral (B) and tetrahedral (A) sites of the spinel structure were determined using X-ray absorption spectroscopy. The analysis of both the X-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the zinc ferrite spinel structures varies with particle size. In particular, in the bulk microcrystalline sample, Zn²⁺ ions are at the tetrahedral sites and trivalent Fe³⁺ ions occupy octahedral sites (normal spinel). When particle size decreases, Zn²⁺ ions are transferred to octahedral sites and the degree of inversion is found to increase as the nanoparticle size decreases. This is the first time that a variation of the degree of inversion with particle size is observed in ferrite nanoparticles grown within an aerogel matrix.