Mise en évidence d'un échange électronique entre Fe2+ ET Fe3+ dans les oxydes rhomboédriques AFe2O4 par spectroscopie mossbauer DU57Fe

The ABB'O₄ rhomboedral oxides containing exclusively either Fe²⁺(InFeGe_0,5Zn_0,5O₄) or Fe³⁺(LuMg-FeO₄ and LuMnFeO₄) are investigated with Mössbauer spectroscopy, in their paramagnetic state.A similar study is made on two mixed oxides containing iron under its two oxidation states, with the $\text{Fe}{}^{\mathrm{2+}}\text{Fe}{}^{\mathrm{3+}}\text{= 2}$ and 1 (InFe_1,5Ga_0,5O₄ and InFe₂O₄) atomic ratio.Comparing the results, we have come to the conclusion that a fast electronic exchange between Fe²⁺ and Fe³⁺ takes place at room temperature. In this structure, point Fe²⁺ and Fe³⁺ are distributed on the same crystallographic site with the point symmetry C_3v. We show that neighbouring effects lower this local symmetry.