SOLID-SOLID INTERACTIONS IN THE NIO FE2O3 SYSTEM WITH AND WITHOUT LIO2 DOPING/

The effects of calcination temperature, molar ratio and Li2O doping on the interaction between ferric and nickel oxides were investigated us ing TG, DTA, dDTA and XRD techniques. The results obtained revealed th at NiO retarded the crystallization of ferric oxide into the alpha pha se and interacted with it to yield a well crystallized NiFe2O4 (trevor ite) at temperatures starting from 700 degrees C. However, the solid-s olid interaction that gives rise to nickel ferrite was found to be aff ected by the molar ratio of NiO and Fe2O3 present. The complete transf ormation of the reacted oxides into the ferrite phase required prolong ed 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. Heati ng of the mixed solids doped with 1.5 mol% Li2O at 800 degrees C led t o 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 o f Li2O in modifying the solid-solid interactions between NiO and Fe2O3 and the formation of beta-LiFe5O8 is discussed in the light of the di ssolution of a portion of Li2O and an increase in the mobility of Ni2 ions in the nickel oxide lattice.