The effects of calcination temperature, molar ratio and Li2O doping on the interaction between ferric and nickel oxides were investigated using TG, DTA, dDTA and XRD techniques. The results obtained revealed that NiO retarded the crystallization of ferric oxide into the alpha phase and interacted with it to yield a well crystallized NiFe2O4 (trevorite) at temperatures starting from 700 degrees C. However, the solid-solid interaction that gives rise to nickel ferrite was found to be affected by the molar ratio of NiO and Fe2O3 present. The complete transformation of the reacted oxides into the ferrite phase required prolonged heating at temperatures above 1100 degrees C. Lithium oxide doping at 700 and 800 degrees C modified the formation of nickel ferrite; the presence of 0.75 or 1.5 mol% of Li2O depressed the ferrite formation, which was, however, enhanced in the presence of 3 mol% of Li2O. Heating of the mixed solids doped with 1.5 mol% Li2O at 800 degrees C led to the formation of beta-LiFeO2, which was converted into alpha- and/or beta-LiFe5O8 by increasing the amount of Li2O to 3 mol%. The effect of Li2O in modifying the solid-solid interactions between NiO and Fe2O3 and the formation of beta-LiFe5O8 is discussed in the light of the dissolution of a portion of Li2O and an increase in the mobility of Ni2+ ions in the nickel oxide lattice.