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

Abstract

Several mixed ferrites MgFexGa2–xO4 and ZnFexGa2–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 MgFexGa2–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 MgFexGa2–xO4 the ratio Fetet/Feoct increases with increasing iron content, while the opposite trend was observed in the ZnFexGa2–xO4 system.