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).