Polyol-Made Spinel Ferrite Nanoparticles—Local Structure and Operating Conditions: NiFe2O4 as a Case Study

We report the effect of a polyol-mediated annealing on nickel ferrite nanoparticles. By combining X-ray fluorescence spectroscopy, diffraction, and 57 Fe Mössbauer spectrometry, we showed that whereas as-prepared nanoparticles (NFO) are stoichiometric, annealed ones (a-NFO) not, since Ni 0 -based crystals precipitate. Nickel depletion from spinel lattice reduction in polyol solvent accompanied with an important cation migration. Indeed, thanks to hyperfine structure analysis, evidenced distribution NFO departs thermodynamically stable inverse concentration tetrahedrally coordinated 2+ 20 wt-% ( A sites). After annealing, demixing, originated very probably sites lattice, phase accommodates anion vacancies, leading (Fe 3+ 0.84 □ 0.16 ) [Ni 0.80 1.16 0.04 ] B O 4-0.20 formula, meaning applied treatment is not so trivial.