Dispersion of dielectric properties of titanium substituted W-type hexaferrites

A series c f polycrystalline hexagonal ferrites with the SrCu2-x/2TixFe16-xO27 (X = 0.0, 0.8, 1.2, 1.6 and 2.0) composition were prepared by using the conventional ceramic technique to investigate their AC conductivity and dielectric properties as a function of frequency (f) and temperature (T). The results of AC conductivity measurements reveal three distinct regions in sigma'(f) curves. The first region covers the range of f <= 10 Hz where dispersion of sigma' was attributed to the interfacial electrode polarization and the grain boundaries effect. The second region in the frequency range of 10 Hz <= f <= 10(4) Hz is characterized by approximately frequency-independent sigma'. In the third region, f >= 10(4) Hz, the AC conductivity obeys the universal power law. The frequency exponent S in the power law was found to decrease with increasing temperature. This behavior suggested that the classical barrier hopping model is the most probable mechanism in these samples. The dielectric loss tangent measurements show dielectric relaxation peaks which were explained on the basis of the assumption that a strong correlation between the conduction mechanism and the dielectric polarization exists in ferrites.