AUTHOR=Gaudisson T. , Nowak S. , Nehme Z. , Menguy N. , Yaacoub N. , Grenèche J.-M. , Ammar S. 

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

JOURNAL=Frontiers in Materials

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.668994

DOI=10.3389/fmats.2021.668994

ISSN=2296-8016

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