• JIJIMON K THOMAS

      Articles written in Bulletin of Materials Science

    • Enhanced infrared transmission characteristics of microwave-sintered Y$_2$O$_3$–MgO nanocomposite

      C T MATHEW SAM SOLOMON JACOB KOSHY JIJIMON K THOMAS

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      Infrared (IR) transparent ceramics are found to have applications in demanding defence and space missions. Inthis work, Y$_2$O$_3$–MgO nanocomposites were synthesised by a modified single-step combustion technique. The characterisation of the as-prepared powder by X-ray diffraction and transmission electron microscopy revealed the presence of cubicphases of ultra-fine nanostructured Y$_2$O$_3$ and MgO, with an average crystallite size of $\sim$19 nm. For the first time the resistive and microwave heatings were effectively coupled for sintering the sample, and it was found that the sintering temperature and soaking time were reduced considerably. The pellets were sintered to 99.2% of the theoretical density at 1430$^{\circ}$C for a soaking duration of 20 min. The well-sintered pellets with an average grain size of $\sim$200 nm showed better transmittance properties relative to pure yttria. The promising percentage transmission of 80% in the UV–visible region and 82% in the mid-IR region shown by Y$_2$O$_3$–MgO nanocomposites can be tailored and made cost-effective to fabricate high-quality IR windows for strategic defence and space missions.

    • Preparation, characterization and properties of LnSmWO$_6$ (Ln $=$ Nd and Dy) nanofunctional ceramics

      N L JAYALEKSHMY JIJIMON K THOMAS SAM SOLOMON

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      Isovalent substitution of lanthanide ions in Ln$_2$WO$_6$ (Ln $=$ lanthanides) nanoceramics can probe into multifunctional applications due to their unique structural and electronic properties. In this work Sm$^{3+}$ ions in the Sm$_2$WO$_6$ nanoceramics were partially replaced with Nd$^{3+}$ and Dy$^{3+}$ ions and their structural, optical and ionic transport propertieswere studied. The size and structure of the nanocrystalline LnSmWO$_6$ (Ln $=$ Nd and Dy) compounds prepared through a combustion method were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM). UV–Visible spectroscopy and photoluminescence spectroscopywere used for the investigation of optical and electronic properties of the nanoceramics. Bulk ceramics prepared from the nanoparticles achieved high-density during the sintering process and the surface morphology of the dense NdSmWO$_6$ was imaged using scanning electron microscopy. The electrical properties of the dense ceramics were analysed using impedancespectroscopy. XRD analysis carried out on the prepared materials showed a single-phase monoclinic structure for the nanoceramics. A combined analysis of FTIR and Raman studies showed the presence of Ln–O and O–W–O vibrations,which confirm the monoclinic structure. Particulate properties investigated through the TEM imaging showed that the prepared materials are polycrystalline aggregates. Optical studies carried out on the nanoparticles showed absorption in the UV region and emission in the visible region. Impedance spectroscopic studies conducted on bulk ceramics imply that these are good oxide ion conductors at high-temperature.

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