Relation between cation distribution and chemical bonds in spinel NiFe2O4

In spinel oxides, the cation distribution plays an important role in determining their technologically important properties. Herein computational predictions based on the first principles calculations are presented to elucidate the relation between cation distribution and chemical bonds in spinel NiFe2O4. The variation of physical properties (such as system energy, lattice parameter, and atomic magnetic moment) with respect to the cation distribution (i.e., degree of inversion) in spinel NiFe2O4 oxide is discussed. This study further reveals that the energy of spinel NiFe2O4 oxide is linearly proportional to the number of different types of cation-oxygen-cation bonds in the spinel structure. The equilibrium degree of inversion in spinel NiFe2O4 at elevated temperatures and the transformation from an ordered to disordered cation distribution in inverse spinel NiFe2O4 are predicted and found to be driven by competition between bond enthalpy and entropy of cation site occupancy.