Correlation of structural and electrical properties in heterovalent substituted Sr-hexaferrites

Abstract

M-type hexagonal ferrites with heterovalent substitutions were synthesized using co-precipitation method. The nominal compositions used were SrFe12−2xCrxZnxO19 (x = 0.0–1.0). X-ray diffractograms of the samples confirmed the hexagonal structure of strontium hexaferrite. The crystallite size was found to be in the range of 42–67 nm. The lattice expands in a non-monotonous way with the extent of dopant concentration. Scanning electron microscopy showed particles like morphology with the estimated particle sizes in the range of 8–11 μm. By varying the frequency (from 1 kHz to 3 MHz) and temperature (from RT to 300°C), the dielectric properties were investigated. Varying both frequency and temperature, the dielectric constant and loss tangent were found to be decreased with increase in frequency. Also, dielectric constant and loss tangent were found to be increased with increase in temperature. At 1 kHz frequency and temperature 300 °C composition (x = 1.0) showed maximum value of dielectric constant. Such a composition can be used for capacitors where high energy storage is required. AC conductivity of all the prepared samples was also found to be increased with increasing the temperature and applied frequency. This phenomenon is exactly in accordance with Jonscher’s power law. The value of exponent ‘n’ used in Jonscher’s power law has been calculated and is found to be decreasing with temperature. Samples followed Correlated Barrier Hoping (CBH) model. The real and imaginary parts of complex impedance were also measured, and these are in accordance with the ac conductivity graphs. Cole-Cole plots were drawn. The plots helped to suggest an equivalent circuit to understand the grain and grain boundary effect in the prepared samples. It was observed that for all the prepared samples grain boundary effect is dominant at 00 °C. Nonsymmetrical and depressed semicircle arcs were also produced that indicate the non-Debye type relaxation processes in the studied compositions.