Frequency Dependent Dielectric Constant Measurements Research Articles

Effect of holmium substitution on the structural, magnetic and transport properties of CoFe2-xHoxO4 ferrites

The effect of Ho3+ substitution on the structural, magnetic and transport properties of a series of CoFe2-xHoxO4 (referred to CFHO) ferrites, (where, x = 0.00–0.20 in steps of 0.05) were studied. All the samples investigated were synthesized by the standard solid state reaction technique. X-ray diffraction (XRD) patterns confirmed the formation of single phase cubic spinel structure in all the compositions. The increases in the values of lattice parameter with the increase in Ho3+ concentrations suggested the expansion of unit cells. Bulk density was found to be decreased, and porosity increased for CFHO with composition x = 0.05 due to some structural distortion. Field emission scanning electron microscopy (FESEM) images showed that Ho3+ had a significant effect on the grain growth of the samples. The substitution of Ho3+ strongly influenced the magnetic characteristics which were confirmed from the magnetization measurements examined by vibrating sample magnetometer (VSM). Curie temperature (Tc) was found to be decreased linearly with the increase of Ho content ascribed to the weakening of A-B exchange interaction. The initial permeability was found to be independent of frequency up to a high frequency region for all the studied composites. All the samples showed very low loss factor at high frequency region and remained almost constant. AC electrical resistivity was found to be decreased with the composition up to 0.15 and then increased for x = 0.20. Frequency dependent dielectric constant measurements showed that Ho3+ substitution improved the dielectric constant values of the CFHO ferrites.

Ferroelectric relaxor properties of (1 − x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 ceramics

The Ba0.5Ca0.5TiO3 (BCT) composition dependent dielectric and structural properties of (1−x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 powders were investigated. Room temperature x-ray diffraction revealed the powder structure to transform from orthorhombic to cubic with increasing BCT composition. The frequency dependent dielectric constant measurements revealed a shift in the temperature of the maximum dielectric constant for at frequencies, suggesting that the system exhibits ferroelectric relaxor behavior. The system containing 15% BCT showed the closest calculated Curie–Weiss exponent to 2, which the exponent for a relaxor ferroelectric.

Thermal and Dielectric Properties of Amorphous LiNbO 3

Amorphous LiNbO3 was produced by the twin-roller quenching method and X-ray diffraction, trace of differential thermal analysis, and temperature- and frequency-dependent dielectric constants were measured. After glass transition and crystallization temperatures were confirmed by differential thermal analysis experiments, activation energies of both processes were calculated using Ozawa's non-isothermal method. From the results of temperature- and frequency-dependent dielectric constant measurements, dielectric relaxation mechanisms below and above glass transition and crystallization temperatures were considered.