A.M. Abo El Ata

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.

Semiconductivity in Ba2Ni2−xZnxFe12O22 Y-type hexaferrites

Abstract The electric, thermoelectric and magnetic properties were studied as a function of temperature and composition for a series of Ba 2 Ni 2− x Zn x Fe 12 O 22 Y-type hexaferrite samples (with x =0, 0.4, 0.8, 1.2, 1.6 and 2) prepared using the usual ceramic technique. The experimental results indicated that the DC electrical conductivity σ DC , thermoelectric power α , diff mobility μ d , carrier concentration n and initial magnetic permeability μ i increase whereas the Fermi energy E F decreases as the temperature increases. α has a negative sign for all samples indicating that the majority of electric charge carriers are electrons. The study of initial magnetic permeability showed two peaks on μ i – T curves. The first peak nearly appears at Curie temperature T c for all samples except for the sample with x =2 while the second peak T s appears below room temperature for all samples. T c decreases due to the replacement of non-magnetic Zn 2+ ions to magnetic Ni 2+ ions. μ i , activation energies for hopping E H , for carrier generation E g and for electric conduction ( E 1 , E 2 and E 3 in regions I, II and III) decreases to reach minimum at x =1.2 and start to increase for x >1.2. Each of σ DC , α , n , μ d and energy at donor level E D increase as the substitution of non-magnetic Zn 2+ ions to magnetic Ni 2+ ions increase reaching maximum at x =1.2 and start to decreases for x >1.2. The small values of μ d and its strong temperature-dependence (exponential relation) indicate that the hopping conduction mechanism is predominant at high temperatures in region III. In region II, the band conduction mechanism shares in electric conduction process beside the hopping conduction mechanism. The band conduction mechanism is predominant in region I.

Conduction mechanism of BaCo2−xNixFe16O27

Abstract A series of W-type hexaferrite samples of BaCo 2− x Ni x Fe 16 O 27 with ( x =0.0, 0.4, 0.8, 1.2, 1.6) were prepared by using the well known ceramic technique to investigate their electrical properties. The results of thermoelectric power coefficient and DC electrical conductivity suggested that the conduction mechanism in this system is due to hopping of electrons between Fe 2+ and Fe 3+ along with the hole transfer between Ni 2+ and Ni 3+ . It was found that the conductivity increases as the replacement of Co 2+ ion by Ni 2+ ion increases. The results of real AC conductivity shows a dispersion with frequency. The dispersion decreases as the temperature increases. The dispersion of AC conductivity was explained on the basis of Koops model.