• K T Mathew

      Articles written in Bulletin of Materials Science

    • Microwave dielectric properties of nanostructured nickel ferrite

      John Jacob M Abdul Khadar Anil Lonappan K T Mathew

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      Nickel ferrite is one of the important ferrites used in microwave devices. In the present work, we have synthesized nanoparticles of nickel ferrite using chemical precipitation technique. The crystal structure and grain size of the particles are studied using XRD. The microwave dielectric properties of nanostructured nickel ferrite samples of three different average grain sizes and those of two sintered samples were studied. The parameters like dielectric constant, dielectric loss and heating coefficient of the nanoparticles samples are studied in the frequency range from 2.4 to 4 GHz. The values of these parameters are compared with those of sintered pellets of the same samples. All these parameters show size dependent variations.

    • Complex permittivity and conductivity of poly(𝑝-phenylenediazomethine) and its blends at microwave frequencies

      K G Princy Rani Joseph Honey John K T Mathew

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      Poly(𝑝-phenylenediazomethine) was synthesized by the condensation reaction between glyoxal and 𝑝-phenylene diamine in different solvents like methanol, toluene, 𝑚-cresol and 𝑁,𝑁-dimethylformamide. The dielectric properties and microwave conductivity of the pelletized samples were measured using cavity perturbation technique. The measurements were done at 2.17 GHz at room temperature (25°C). The effect of dopants on the dielectric properties and conductivity was studied using HCl and HClO4. Dielectric properties like dielectric constant, dielectric loss factor and microwave conductivity increased on doping with HCl and HClO4. Conducting polymer composites were prepared by in situ polymerization of glyoxal and 𝑝-phenylenediamine in different solvents containing different amounts of PVC, and silica. The microwave conductivity and complex permittivity of each sample was measured. The effect of dopants like HClO4 and HCl on these dielectric properties was also studied. The d.c. conductivity of the pressed samples measured by the two-probe method was also studied.

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