Optical spectra and energy band gap of Ni-Zn ferrite

Photoacoustic Spectroscopy (PAS) has been used to study solid NI-Zn ferrite powder. Samples of structural formula Ni0.7+xZn0.3TixFe2-2xO4 (x = 0.0 - 1 .0 wt%) are prepared by solid state reaction. PA spectra show four absorpti on peaks at similar to 312, similar to 297,similar to 275 and similar to 26 0 mu. Peak intensity decreases rapidly with increasing energy. The peaks at 312 and 260 nm are assigned to 3d electrons transitions of Fe3+ and the 29 7 and 275 mn peaks are most likely due to charge transfer transitions from oxygen to Fe(oct) and Fe(tetra). The peak at 297 run disappears gradually w hen Ti substitution is increased. We attempted to establish the Ti effect b y considering the fact that when Ti is substituted into the ferrite lattice , it is expected that the valence orbitals of the Ti ions mix covelantly wi th the 2p valence orbitals of the surrounding oxygen atoms. A similar mixin g will also occur between the iron 3d orbitals and the Ti orbitals via the intervening oxygen atoms. We have also recorded PA spectra of Fe2O3, ZnO, N iCO3 and TiO2. By observing the position of the peaks and intensities, we h ave arrived at the conclusion that Fe3+ ions govern the structure of base f errite. For the first time, we have determined the energy band gap of such materials from their PA spectra.