Dependence of the cation distribution in Manganese ferrite, MnFe₂O₄, on temperature and oxidation

Abstract

The cation distribution of manganese ferrite among the tetrahedral and octahedral sites was determined for (Mn_xFe_1-x) ?? Mn_yFe_{2-y-d?? d}??O₄, using the X-ray anomalous dispersion. The specimen had a fixed Mn/Fe ratio and were synthesized under various temperatures and equilibrium oxygen partial pressures. The variation of the lattice constant and the oxygen parameter, and the local distortion of the octahedral sites were found to be strongly dependent on the cation distribution.
With a decreasing oxygen partial pressure, a larger amount of Mn was, distributed at the tetrahedral sites, while Fe increased at the octahedral sites. Noticeable temperature dependence of the cation distribution was not confirmed because of the presence of increasing cation vacancy at the octahedral sites with lowering the quenching temperature. This fact may be ascribed to varying oxidation of Mn and Fe with temperature.
The large influence of the cation vacancy on the site occupancy of the ferrite was discussed, based on the valency states of the constituent atoms at each site. The distribution of the charge in the ferrite may be schematically summarized in the form:
(Mn²⁺ _tFe³⁺ _1-t+1/8d) ??Mn³⁺ _1-t-uMn²⁺ _u Fe²⁺ _1-t-u-dFe³⁺ _2t+u+7/8d??_3/8d ?? O_4+1/2d