IR absorption spectroscopic study of mixed cobalt substituted lithium ferrites

The IR spectra of Li0.5−(x/2)CoxFe2.5−(x/2)O4 ferrite samples (0≤x≤0.6) prepared by solution combustion method have been reported. The influence of Co substitution is verified. XRD studies confirm the spinel phase formation of ferrites. Lattice constant varies linearly from 8.31 Å (x=0) to 8.35 Å (x=0.6) with composition. Evidence of two absorption bands in the IR spectra (below 800 cm−1) reveals the characteristic feature of spinel ferrite. The IR spectra featured additional three absorption bands around 550, 670 and 705 cm−1 for the samples x=0.1 and x=0.6. Absence of bands splitting specifies that Fe ions do not exist in excess form. It is found that high frequency band (ν1), due to tetrahedral (A) group, lies at around 600 cm−1 and low frequency band (ν2), due to octahedral (B) group, around 450 cm−1. The positions of bands are found to be composition dependent. The IR bands due to tetrahedral complexes shift slightly towards high frequency side with composition upto x=0.4 where as that due to octahedral complexes shift towards lower frequency side with x. Based on the data of absorption bands, force constants (kt, ko) and bond lengths (RA, RB) were estimated. Compositional dependence of force constants is explained on the basis of cation–oxygen bond distances of respective sites and cation distribution.