The structural evolution of Fe₂O₃–SiO₂ nanocomposite samples prepared using the sol–gel method have been studied by EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) techniques in comparison with pure nanosized and microcrystalline maghemite samples. EXAFS data show that the difference between nanosized and microcrystalline maghemite is due to an increase of disorder of the superficial sites while no decrease of coordination numbers was detected. EXAFS and XANES data of the nanocomposite thermally treated at 900°C indicate that the sample is constituted by maghemite nanoparticles embedded into amorphous silica while the sample thermally treated at 300°C contains an amorphous precursor which is very likely to be ferrihydrite. No interactions between the metal oxide nanoparticles and the silica network are present since the EXAFS spectra of the nanocomposite samples can be interpreted as only having Fe–O and Fe–Fe interactions.

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Mn K-edges were used to investigate the formation of MnFe₂O₄nanoparticles embedded in a silica aerogel matrix as a function of calcination temperature (at 450, 750 and 900 °C). Up to 450 °C, two separated highly-disordered phases of iron and manganese are present. With increasing the temperature (to 750 and 900 °C), the structure of aerogel nanoparticles becomes progressively similar to that of the spinel structure MnFe₂O₄ (jacobsite). Quantitative determination of cations distribution in the spinel structure shows that aerogels calcined at 750 and 900 °C have a degree of inversion i = 0.20. A pure jacobsite sample synthesised by co-precipitation and used as a reference compound shows a much higher degree of inversion (i = 0.70). The different distribution of iron and manganese cations in the octahedral and tetrahedral sites in pure jacobsite and in the aerogels can be ascribed to partial oxidation of Mn²⁺ to Mn³⁺ in pure jacobsite, confirmed by XANES analysis, probably due to the synthesis conditions.