We investigate the local structure of nanoparticles based on a manganese ferrite core surrounded or not by a maghemite layer obtained after hydrothermal surface treatment. Results of X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) measurements are crossed with those of infield Mossbauer spectroscopy and X-ray absorption spectroscopy (XANES/EXAFS) to study the valence state of Mn ions and the cation distribution at interstitial sites of the core−shell nanoparticle structure. Linear combination fitting of XANES data clearly indicates the existence of mixed valence states of Mn cations in the Mn ferrite phase. As a direct consequence, it induces nonequilibrium cation distributions in the nanoparticle core with the presence of a large amount of Mn cations at octahedral sites. The quantitative results of the inversion degree given by NPD, Mossbauer spectroscopy measurements, and EXAFS are in good accordance. It is also shown that both the proportions of each oxidation degree of Mn ions and their location at tetrahedral or octahedral sites of the spinel nanocrystal core can be modified by increasing the duration of the surface treatment. a χ M is the molar fraction of manganese ions obtained by ICP and AAS techniques, ⟨a⟩ is the average lattice parameter deduced from Bragg's law, ϕ c / ϕ is the volume fraction of the core, and t sh is the thickness of the surface layer. The particle sizes (D XR ) were obtained by Scherrer's equation.

We investigate the local structure of nanoparticles based on cobalt ferrite core with and without a hydrothermal surface treatment of variable duration of time that promotes a coating shell by crossing information obtained from atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), neutron powder diffraction (NPD), and X-ray absorption spectroscopy (XAS) measurements. Chemical titration results show that the surface layer thickness increases as the duration of the surface treatment increases. The cation distribution obtained by Rietveld refinement of NPD patterns allows splitting the core and shell structural parameters obtained from Rietveld refinement of XRD data of the samples well described in a core-shell model. We follow the local structural evolution with the surface treatment time analyzing both XANES and EXAFS regions of the absorption spectrum. As a result, we observe that the surface treatment is not energetically strong enough to provoke changes on the mean oxidation states of the cations in the spinel structure; indeed, the interatomic distances are similar to those found in bulk materials and the inversion degree remains the same after the surface treatment, in good accordance with the cation distribution obtained by Rietveld refinement of NPD data.