Structural and Dielectric Study of Nano-Crystalline MFe_12 O_19 (M=Ba and Sr) Hexaferrites Prepared Via Sol-Gel Auto-Combustion Techniques

Abstract

The structural and electrical properties of m-type hexaferrites are very sensitive to particle size, shape and degree of crystalinity. The syntheses techniques and the nature of cations in the material lead to significant change in electromagnetic properties of the materials. In this work, M-type  and  nanohexaferrites were successfully synthesized via sol-gel auto-combustion techniques. The structural, dielectric and functional group of these nanoparticles was investigated using XRD, FTIR, and Impedance analyzer. The XRD analysis revealed that pure and single phase hexagonal ferrites with crystallites sizes of 33.35nm for and 32.29nm for were obtained. The lattice constant slightly varies due to variation of ionic radii in the samples.  The FTIR spectra of the sample show three dominants peaks in the range 400-600 cm^-1 which indicate the formation of the desired hexaferrites structure. The dielectric properties were studied using impedance measurements obtained in the frequency range 100Hz-120MHz. The dielectric constant, dielectric loss and conductivity were analysed using Maxwell-Wagner model. Dielectric constant was enhanced at high frequency in the entire sample and reduction of dielectric loss is also observed with further ions substitutions. The grain boundary resistance contributes the most to the dielectric properties as indicated by Nyquist plot, whereas the Ac conductivity is the dominant conducting mechanism in the material. A high dielectric property, low energy dissipation and higher conductivity were observed with at higher frequency these make it useful for higher frequency applications.