S.M. Attia

Effect of tetravalent titanium ions substitution on the dielectric properties of Co-Zn ferrites

Abstract A series of polycrystalline spinel ferrites with composition Co 0.4 Zn 0.6+ X Ti X Fe 2−2 X O 4 , ( X =0.1, 0.2, 0.3, and 0.4) were prepared by the standard ceramic method to study the effect of Ti ions substitution on their AC electrical conductivity and dielectric properties at different frequencies and temperatures. It was found that the electrical conductivity decreases as Ti ions substitution increases. The results of electrical conductivity were explained on the basis of the polaron conduction mechanism. The results of the dielectric constant and dielectric loss were explained with the aid of Rezlescu model and Koops phenomenological theory.

Dielectric behaviour of CuCr ferrites

Abstract Samples of the system CuFe 2− x Cr x O 4 where x = 0.0, 0.2, 0.4, 0.6 and 0.8 were prepared. The dielectric constant and dielectric loss were measured at different frequencies and temperatures from room temperature to 600 K. The dielectric constant was measured using the phase detector technique (lock-in amplifier). The results showed that the dielectric loss decreases with increasing frequency and Cr substitution. The dielectric constant decreases with both increasing frequency and Cr substitution at room temperature. At moderate temperatures, the dielectric constant shows a dispersion peak e ′ max , and this peak shifted to higher frequency with increasing temperature. The results are explained in the light of the fact that the dielectric polarization process is similar to that of conduction. The appearance of the dispersion peak is related to the contribution of two types of charge carriers.

Ac conductivity in CuCr ferrites

Abstract Samples of the type CuFe 2− x Cr x O 4 with x = 0.0, 0.2, 0.4, 0.6 and 0.8 were prepared. Ac conductivity measurements were carried out at different frequencies up to 10 5 Hz and at various temperatures from room temperature up to about 550 K. The ac conductivity was measured using the phase detector technique (lock-in amplifier). The results showed that the conductivity increases with both temperature and frequency, and the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region. At high temperatures the conductivity becomes frequency independent. We conclude that the conductivity in these ferrites consists of two kinds of conduction mechanisms.

Semiconductive properties of CuCr ferrites

Abstract Samples of type CuFe 2- x Cr x O 4 , where x = 0.0, 0.2, 0.4, 0.6, and 0.8, were prepared by the usual ceramic technique. The X-ray measurements confirmed that all samples were of spinel type of tetragonal crystal structure. The lattice parameter, density, theoretical density, and porosity were determined at different Cr substitutions. Dc resistivity (ρ) and thermoelectric power (α) were measured at temperatures differing from room temperature up to 580 K. The drift mobility μ n for n-carriers within the sample was calculated at various temperatures. The results indicated that the samples have semiconducting behavior. At room temperature the majority carriers are electrons, except in case x = 0.8. The Curie temperature T c shifts to higher temperature with increasing Cr substitution. The drift mobility μ n increases exponentially with temperature. The results are in good agreement with previous results.