IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 7, Issue 6 Ver. I (Nov. - Dec. 2015), PP 71-76 www.iosrjournals DOI: 10.9790/4861-07617176 www.iosrjournals.org 71 | Page Dielectric Properties in Co-Ti Doped CaSrM Hexaferrites M. R. Eraky Physics Department, Faculty of Science, Kafrelsheikh University, 33516 El Geesh Street, Kafr El Sheikh, Egypt Abstract: The dependence of dielectric constant ' and dielectric loss tangent tan  on frequency and composition have been investigated at fixed temperatures for polycrystalline Ca 0.5 Sr 0.5 Co x Ti x Fe 12-2x O 19 (where 0.0 ≤ x ≤ 0.8) hexaferrites samples prepared by ceramic method. The measurements reveal that the samples under investigation have high values of ' reached to 10 6 at 1 KHz and 600K. The experimental results indicated that ' and tan  decrease as the frequency increases and temperature decreases. The studied samples showed an abnormal dielectric loss (or relaxation peaks) which were shifted towards higher frequency as the temperature increases. ' and tan  increase as Co and Ti ions substitution increases up to x≤0.4, after that both parameters decreases. The activation energy for dielectric relaxation, E D , was estimated for the samples. It is shown that, E D , have low values (~0.08- 0.18 eV) and have inverse proportional with the dielectric constant '. Keywords – Dielectric properties, Doped M ferrite, Loss in ferrite, Dielectric relaxation, Activation energy. I. Introduction The hexagonal ferrites (M-type) have been attracted a considerable attention in technological and scientific research because of their high electrical resistivity, low eddy current, high Curie temperature, high stability and easy manufacturing. M hexaferrite is used as a basic material for permanent magnets, magnetic recording media, microwave and high frequency devices [1-3]. The polycrystalline ferrites are very good dielectric materials. During the process of preparation of ferrites in polycrystalline form, when the ferrite powder is sintered under slightly reducing conditions, the impurity ions such as Fe 2+ were formed in the ferrite lead to high-conductivity grains. The grain boundaries are formed during the sintering process due to superficial reduction or oxidation of crystallites as a result of direct contact with the firing atmosphere [4]. Thus, the ferrite can be considered as high conductive grains separated by thin low conductive layers (grain boundaries) and behave as inhomogeneous dielectric materials. The AC electric field on the specimen is concentrated in the grain boundary regions. Therefore, dielectric properties are affected by grain boundary phase and the defect distribution in ferrites. However, the dielectric behavior is one of the most important properties of ferrites which very sensitive to the preparation conditions, such as; sintering time, sintering temperature and atmosphere, type and quantity of additives [5, 6]. The study of dielectric properties produces valuable information on the behavior of the localized electric charge carriers leading to greater understanding of the mechanism of dielectric polarization in these studied ferrite samples. The dielectric behavior of Ca 0.5 Sr 0.5 Co x Ti x Fe 12-2x O 19 hexaferrite was not treated before in the literature. Therefore, the author aimed to study the effect of frequency, temperature and Co and Ti ions substitution on real dielectric constant and loss factor for the samples Ca 0.5 Sr 0.5 Co x Ti x Fe 12- 2x O 19 (0≤x≤0.8). II. Materials And Method Polycrystalline samples CaSrCoTiM hexaferrites having the general formula Ca 0.5 Sr 0.5 Co x Ti x Fe 12-2x O 19 (where x= 0.0, 0.2, 0.4, 0.6 and 0.8) were prepared by a conventional double sintering ceramic method. The single phase M type hexagonal structure, lattice parameters, densities and porosity of these samples were checked by X-ray powder diffraction measurements. The details of the method of preparation and X-ray measurements were reported earlier [7]. The real dielectric constant ' and loss tangent factor tan  of the samples were measured at room temperature in static air by the two probe method using an RLC bridge (model Hoki 3532-50 LCR HiTESTER). The values of loss tangent tan  and the capacitance of the sample (C) were recorded directly from the bridge. The dielectric constant, ', was calculated using the relation: ' = Cd /    (1) where ٬ d ٫ is the thickness of the sample, ٬ A ٫ is the cross section area of the sample and ٬   ٫ is the permittivity of free space (     F.m -1 ). This work was carried out at materials science laboratory, Physics Department, Faculty of Science, Kafrelsheikh University, Egypt.