Structural characterization of polycrystalline gallium-substituted magnesium ferrites (MgFexGa2–xO4) and zinc ferrites (ZnFexGa2–xO4)

Abstract

Several mixed ferrites MgFe_xGa_2–xO₄ and ZnFe_xGa_2–xO₄ have been prepared, in polycrystalline form, by solid-state reaction at 1273 K of mixtures of the individual metal oxides (MgO, Fe₂O₃ and Ga₂O₃ in the first case, and ZnO, Fe₂O₃ and Ga₂O₃ in the second). The resulting materials were found to have spinel-type structure. X-Ray powder diffractometry was used to determine the cubic unit-cell length, the oxygen positional parameter, u, and the distributions of the different cations in tetrahedral and octahedral coordination. For the oxygen parameter the value u= 0.380 ± 0.002 was found for all samples in the MgFe_xGa_2–xO₄ system. Ferrites containing zinc gave u= 0.385 ± 0.002. This larger value of u was considered to be due to the location of the large Zn²⁺ ion in tetrahedral sites. Zn²⁺ was found to have a greater tetrahedral preference than either Fe³⁺ or Ga³⁺. Magnesium–gallium ferrites were all found to be nearly inverted spinels, where Fe³⁺ and Ga³⁺ compete for the available tetrahedral interstices while Mg²⁺ is located mainly on octahedral sites. The relative ionic partition of Fe³⁺ was found to be strongly dependent upon chemical composition. For the system MgFe_xGa_2–xO₄ the ratio Fe_tet/Fe_oct increases with increasing iron content, while the opposite trend was observed in the ZnFe_xGa_2–xO₄ system.