Cation distribution and non-stoichiometry in MnCr 2O 4-NiCr 2O 4 spinel solid solutions at 1300 °C

Abstract

The cation distribution in MnCr 2O 4-NiCr 2O 4 spinel solid-solutions at 1300 °C was calculated using non-linear disordering enthalpies obtained from the experimental cation distribution of Mn 2+, Mn 3+, Cr 2+, Cr 3+, Ni 2 and assuming random mixing on both tetrahedral and octahedral sites. The model also incorporates the electron exchange reaction, Mn 2+ + Cr 3+ ai Mn 3+ + Cr 2+, as well as site exchanges of newly formed cations. The Gibbs free energy of mixing derived from the available experimental data obtained in our laboratory is discussed in conjunction with the values calculated from the cation distribution model with the free energy electron redox reaction being a parameter. The effect of size mismatch of the substituting cations was taken into account using a solution model. Observed positive deviations from ideality suggest a miscibility gap at lower temperatures.