• Sam Solomon

      Articles written in Bulletin of Materials Science

    • Synthesis, characterization, sintering and dielectric properties of nanostructured perovskite-type oxide, Ba2GdSbO6

      C Vijayakumar H Padma Kumar Sam Solomon J K Thomas P R S Warriar J Koshy

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      Nanoparticles of barium gadolinium antimonate (Ba2GdSbO6), a complex perovskite-type oxide, has been synthesized using an auto ignition combustion process for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba2GdSbO6 and has a complex cubic perovskite (A2BB′O6) crystalline structure with lattice constant, 𝑎 = 8.449 Å. The TEM image reveals that the particle size of the as-prepared nano powder was in the range 30–60 nm. The nanocrystals of Ba2GdSbO6 synthesized by the combustion technique could be sintered to 96% of the theoretical density by heating at a temperature of 1560°C for a short duration of 3 h. The surface morphology of the sintered pellet has been studied by scanning electron microscope (SEM). The dielectric constant ($\varepsilon_{r}$) was 20 and the loss factor (tan𝛿) was 0.03 at 3 MHz. By the present combustion technique a phase pure nanopowder of Ba2GdSbO6 could be obtained by a single step process without the need of any calcination step.

    • Influence of lead oxide addition on LnTiTaO6 (Ln = Ce, Pr and Nd) microwave ceramics

      H Padma Kumar J K Thomas Annamma John Sam Solomon

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      The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.

    • Behaviour of LaAlO3+LnTiTaO6 (Ln= Ce, Pr or Nd) dielectric ceramic mixtures

      Sam Solomon

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      The 0.1LaAlO3+0.9LnTiTaO6 (Ln= Ce, Pr or Nd) ceramics are prepared through solid state ceramic route. The structure of the materials is studied using X-ray diffraction analysis. The microstructure is analysed using scanning electron microscopy. The dielectric properties in the radio as well as in the microwave frequencies are measured and discussed. The photoluminescence of a representative sample is also analysed. The dielectric constant (𝜀r) and temperature coefficient of resonant frequency (𝜏f) are tailored without appreciable change in the quality factor. The measured values of 𝜀r and 𝜏f are compared with the corresponding predicted values. These mixtures can be made useful in optical and microwave communication.

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


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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.

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