Thermodynamic properties of NiCr₂O₄-NiFe₂o₄ spinel solid solution

The tie lines delineating ion-exchange equilibria between NiFe₂O₄- NiCr₂O₄ spinel solid solution and Fe₂O₃Cr₂O₃ corundum solid solution were determined at 900, 1000, and 1200 °C by electron microprobe and energy dispersive X-ray analysis of oxide phases, using the flux growth technique. Activities of the spinel components were calculated from the tie lines, assuming Temkin's ideal mixing in the corundum solid solution. The spinel phase could be expressed by a regular solution with negative deviations from ideality. The Gibbs free energies of mixing for spinel solid solution were discussed in terms of the cation distribution model, based on site preference energies and assuming random mixing on both tetrahedral and octahedral sites.