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 Ni_0.7+xZn _0.3Ti_xFe_2-2mO₄ (x=0.0-1.0 wt%) are prepared by solid state reaction. PA spectra show four absorption peaks at ~312, ~297, ~275 and ~260 nm. Peak intensity decreases rapidly with increasing energy. The peaks at 312 and 260 nm are assigned to 3d electrons transitions of Fe³⁺ and the 297 and 275 nm peaks are most likely due to charge transfer transitions from oxygen to Fe(oct) and Fe(tetra). The peak at 297 nm disappears gradually when Ti substitution is increased. We attempted to establish the Ti effect by 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 with the 2p valence orbitals of the surrounding oxygen atoms. A similar mixing 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, NiCO₃ and TiO ₂. By observing the position of the peaks and intensities, we have arrived at the conclusion that Fe³⁺ ions govern the structure of base ferrite. For the first time, we have determined the energy band gap of such materials from their PA spectra