Investigation of the MgO:Fe system using the Mossbauer effect

Abstract

The MgO¦Fe system as subjected to a variety of heat-treatments has been studied using the mossbauer effect for Fe⁵⁷. On firing the MgO:Fe samples in air, iron initially dissolves in the lattice in its ferric state and is associated with a charge-compensating vacancy. However, on exceeding a certain concentration, magnesioferrite precipitates out. Hydrogen firing of these samples tends to create clusters of metallic iron and Fe²⁺ at Mg²⁺ sites. On refiring the samples in air, metallic iron is converted to Fe₂O₃ and Fe²⁺ to Fe³⁺ which subsequently reacts with the lattice to give magnesioferrite and a small fraction of Fe³⁺ dissolved in the lattice. These changes are found to be completely reversible. In some cases the magnesioferrite particle size is so small that it exhibits superparamagnetism. Although there is a limit to the solubility of Fe³⁺ in MgO, Fe²⁺ can be dissolved to any extent.