S. K. Chawla

Comparative Dielectric Analysis of Co-Zr Doped M-Type Barium Hexaferrites BaCoxZrxFe(12-2x)O19 Prepared by Different Wet Chemical Routes

Samples of barium hexaferrites (BaCoxZrxFe(12-2x)O19) with varying molar concentration of Cobalt and Zirconium were synthesized successfully by three different wet chemical routes: Sol gel, Citrate and self-combustion. Dielectric constant, dielectric loss tangent and AC Conductivity measurements were carried out in the frequency range 20Hz–1MHz over Impedance analyzer. Dielectric constant and loss tangent variations are explained on the basis of Maxwell-Wagner interfacial polarization in accordance with Koops phenomenological theory. AC Conductivity varies in accordance to Jonscher law (σac = σdc + Aωn) and shows normal behavior shown by other ferrites. The observed behavior of these samples suggests that the materials are suitable for applications in microwave devices. Three wet chemical routes are compared and it can be concluded that samples synthesized by citrate method are showing higher dielectric constant, low loss and low conductivity, hence are better.

Effects of Temperature Variation on Dielectric Properties of Ba4(La(1 - z)Biz)9.33Ti18O54 Solid Solutions

Bi modified Ba4La9.33Ti18O54 solid solutions were synthesized by conventional mixed oxide route. The three composition with molar formula Ba4(La(1 - z)Biz)9.33Ti18O54 where z = 0.0, 0.1 and 0.2 were characterized for structural and dielectric properties. A detailed study related to variation in dielectric properties namely dielectric constant and dielectric loss with change in temperature from 298 K to 423 K was carried out in the frequency range 10 kHz–10 MHz. It was observed that dielectric constant decreases as the temperature increase from 298 K to 423 K in the entire frequency range for all the three samples. There was very small change in dielectric loss. The temperature coefficient of resonant frequency was estimated to improve from 273.8 ppm/K to 54.5 ppm/K as Bi contents increases from z = 0.0 to 0.2. Such materials would be a suitable candidate for applications in mobile communications.

Effect of precursors on dielectric properties of Co-Zr doped strontium hexaferrites in 20 Hz – 120 MHz frequency range

ABSTRACT Cobalt and zirconium doped ferrite pellets of composition are synthesized successfully using the sol-gel method with two different precursors: Citric Acid and Tartaric Acid. Dielectric constant and dielectric loss tangent measurements are performed in the frequency range 20 Hz − 120 MHz over Impedance analyzer. A.C. conductivity is calculated from Debyes equation of complex permittivity. Dielectric constant and loss tangent are found to be varying in accordance to Maxwell-Wagner theory of interfacial polarization. A.C. conductivity is found to increase with increase in frequency as well as doping amount. Dielectric analysis of two series concludes that ferrites prepared using tartaric acid have higher values of dielectric properties at lower frequencies in comparison to those prepared with citric acid, while at higher frequencies, the effect of precursors seems to be insignificant. The enhancement of dielectric constant and dielectric loss with increase in dopant concentration suggests that these samples are promising materials for applications in microwave devices.

Absorption Properties of Lanthanum and Samarium Substituted Barium Titanates

This paper deals with the investigation of structural and absorption properties of microwave dielectric ceramics with the general formula Ba6–3xR8+2xTi18O54 where R = La, Sm and x = 2/3. The X-ray diffraction analysis revealed tungsten bronze type crystal structure with orthorhombic symmetry for these ceramics. The scanning electron micrograph shows uniform needle like elongated grains. Absorption properties i.e. absorption loss, return loss and insertion loss have been measured for the synthesised samples with respect to the frequency in the range 8.0 GHz–12.0 GHz at room temperature.