This may be related to structural changes, since at this heat treatment temperature only the crystalline phase of lithium ferrite is present. The same tendency as the one observed in the ac conductivity regime, in the samples with only one crystal phase, LiFe 5 O 8. Table 3 resumes all the activation energies of the relaxation process. Table 3.
In the literature [ 28, 29 ], the magnetization of the lithium ferrite is around 60 emu/g, which is rather lower than the one obtained in this work ( Figure 16 ). In these samples, the generation of the lithium ferrite phase takes to the decrease in the contribution of the α-Fe 2 O 3 particles with low magnetization.
As described in detail in our recent papers [ 5, 12, 13 ], the solid-state method was used to prepare lithium ferrite (LiFe 5 O 8) powders starting with iron (III) nitrate (Fe (NO 3) 3 .9H 2 O) and lithium nitrate (LiNO 3 (Merck KGaA, Darmstadt, Germany).
The cubic lithium ferrite ( Figure 1 ), spinel LiFe 5 O 8 [ 7], is one of the most important ferrites, and it belongs to the soft ferrite materials group, with high Curie temperature (620°C) [ 8 ], square hysteresis loop and high magnetization.
The spinel lithium ferrite has been widely studied and confirmed to have two crystalline forms: β-LiFe 5 O 8 ( Fd3m space group), known as the disordered LiFe 5 O 8, and the α-LiFe 5 O 8 (space group P4 1 32/P4 3 32 ), called ordered spinel phase.
In the sample treated at 1200°C besides lithium ferrite peaks, the lithium ferrate (Li 2 FeO 3) phase is also detected. The presence of this phase can be explained through the chemical reaction, Eq. ( 2 ), where the peak characteristics of Fe 3 O 4 are also present.