IR absorption and dielectric properties of Li-Ti ferrite

Samples of the system Li0.5+0.5xTixFe2.5-1.5xO4 (x = 0, 0.1, ..., 0.7) were prepared by the usual ceramic technique. IR absorption spectra were used for analysing the compositions. The AC conductivity <(sigma)over tilde (omega)> and dielectric properties (loss tangent tan delta, dielectric constant epsilon' and dielectric loss epsilon `') have been measured at various frequencies and temperatures. Three bands were observed in the IR spectra. The band at around 600 cm(-1) (nu(1){*}) and another one at around 400 cm(-1) (nu(2){*}) were assigned to the tetrahedral and octahedral complexes, respectively. A small band (nu(3)) at around 335 cm(-1) indicated the octahedral divalent metal-oxygen bond in these complexes. The threshold frequency for the electronic transition seems to increase with increasing Ti4+ content, namely with decreasing Fe3+ concentration. At room temperature (RT), the AC conductivity exhibits dispersion in the frequency range from 3 x 10(2) Hz to 5 x 10(5) Hz. The variation of tan delta with frequency at RT shows a peak in the range (2-6) x 10(5) Hz. The electrical conduction mechanism was explained in terms of the electron hopping model. Both effects (temperature and frequency) tend to increase epsilon' and epsilon `'. The composition dependence of the dielectric properties is divided into two regions. The first one is for x < 0.5 (for which long-range order is predominant) and the second one is for x greater than or equal to 0.5 (for which short-range order is predominant).