• M Abdul Khadar

      Articles written in Bulletin of Materials Science

    • Dielectric properties of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites

      S Sankara Narayanan Potty M Abdul Khadar

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      The dielectric properties of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites at different frequencies have been studied over a temperature range covering the stability range of β phase of Ag2HgI4 and beyond the β to a phase transition temperature. έ′, tan δ and σa.c. of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites were found to be larger than the reported values for polycrystalline pellets of Ag2HgI4. The dielectric properties of the nanocomposites were found to be a function of the wt.% of nano alumina. The observed changes are attributed to the grain boundary properties of nanophase materials and to the microsize space charge effects.

    • Optical properties of 60B2O3–(40–𝑥)PbO–𝑥MCl2 and 50B2O3–(50–𝑥) PbO–𝑥MCl2 (M = Pb, Cd) glasses

      Shajo Sebastian M Abdul Khadar

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      Optical absorption and transmittance spectra of 60B2O3–(40–𝑥)PbO–𝑥MCl2 and 50B2O3–(50–𝑥) PbO–𝑥MCl2 (M = Pb, Cd) (10 ≤ 𝑥 ≤ 20) glasses of varying composition were recorded in the UV-visible region. Various optical parameters such as optical energy gap (𝐸opt), Urbach energy (𝐸e), refractive index (𝑛0), optical dielectric constant (𝜀), and ratio of carrier concentration to the effective mass (𝑁/𝑚*) were determined. The variation of optical energy gap with increase in the concentration of PbCl2 or CdCl2 is discussed.

    • Study of optical phonon modes of CdS nanoparticles using Raman spectroscopy

      Rajeev R Prabhu M Abdul Khadar

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      The reduction in the grain size to nanometer range can bring about radical changes in almost all of the properties of semiconductors. CdS nanoparticles have attracted considerable scientific interest because they exhibit strongly size-dependent optical and electrical properties. In the case of nanostructured materials, confinement of optical phonons can produce noticeable changes in their vibrational spectra compared to those of bulk crystals. In this paper we report the study of optical phonon modes of nanoparticles of CdS using Raman spectroscopy. Nanoparticle sample for the present study was synthesized through chemical precipitation technique. The CdS nanoparticles were then subjected to heat treatment at low temperature (150°C) for extended time intervals. The crystal structure and grain size of the samples were determined using X-ray diffraction and HRTEM. The Raman spectra of the as-prepared and heat treated samples were recorded using conventional Raman and micro-Raman techniques. The spectrum of as prepared sample exhibited an intense, broad peak at 301 cm-1 corresponding to the LO phonon mode. Higher order phonon modes were also observed in the spectra. A noticeable asymmetry in the Raman line shape indicated the effect of phonon confinement. Other features in the spectra are discussed in detail.

    • 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.

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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