• Kedar Singh

      Articles written in Bulletin of Materials Science

    • Simultaneous measurements of thermal conductivity and diffusivity of Se80Te20–𝑥In𝑥 (𝑥 = 2, 4, 6 and 10) chalcogenide glasses at room temperature

      N S Saxena Mousa M A Imran Kedar Singh

      More Details Abstract Fulltext PDF

      Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se80Te20–𝑥In𝑥 (𝑥 = 2, 4, 6 and 10) glasses, prepared under a load of 5 tons were carried out at room temperature using transient plane source (TPS) technique. The measured values of both thermal conductivity and diffusivity were used to determine the specific heat per unit volume of the said materials in the composition range of investigation. Results indicated that both the values of thermal conductivity and thermal diffusivity increased with the addition of indium at the cost of tellurium whereas the specific heat remained almost constant. This compositional dependence behaviour of the thermal conductivity and diffusivity has been explained in terms of the iono-covalent type of bond which In makes with Se as it is incorporated in the Se–Te glass.

    • Kinetics of Ge20Se80–𝑥As𝑥 (𝑥 = 0, 5, 10, 15 and 20) in glass transition region

      Kedar Singh N S Saxena

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      The results of differential scanning calorimetric (DSC) measurements on Ge20Se80–𝑥As𝑥 (𝑥 = 0, 5, 10, 15 and 20) system with the specific aim of investigating the effect of heating rate and composition on glass transition temperature have been discussed. The results indicate that the glass transition temperature (𝑇𝑔) is dependent both on the heating rate and composition. The glass transition activation energy (𝐸𝑡) and heat absorbed in glass transition region (𝛥𝐻) are higher for Ge20Se65As15 as compared to the values of other compositions of arsenic. An effort has also been made to develop an empirical model for the composition dependence of 𝛥𝐻. A good agreement has been observed between the experimental values and the results of model calculation.

    • Morphological evolution in single-crystalline Bi2Te3 nanoparticles, nanosheets and nanotubes with different synthesis temperatures

      Punita Srivastava Kedar Singh

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      A general surfactant-assisted wet chemical route has been developed for the synthesis of a variety of bismuth telluride (Bi2Te3) single-crystalline nanostructures with varied morphologies at different temperatures in which hydrazine hydrate plays as an important solvent. Bi2Te3 sheet grown nanoparticles, nanosheets and nanotubes have been synthesized by a simplest wet chemical route at 50, 70 and 100 °C within 4 h. Bi2Te3 sheet grown nanoparticles are obtained in agglomerate state and they are found with many wrinkles. Various types of Bi2Te3 nanotubes are also found which are tapered with one end open and the other closed. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern and energy dispersive X-ray (EDX) spectroscopy were employed to characterize the powder product. It is found that all nanoparticles, nanosheets and nanotubes are well-crystallized nanocrystals and morphologies of the powder products are greatly affected by different synthesis temperatures. The formation mechanisms of bismuth telluride nanostructures are also discussed.

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