• D Chakravorty

      Articles written in Bulletin of Materials Science

    • Relaxation studies on V2O5-TeO2 glasses using heterogeneous conductor model

      M Pal S K Saha D Chakravorty

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      The dielectric modulus spectra of glasses in the system V2O5-TeO2 have been studied as a function of frequency in the temperature range 230 to 330K. A heterogeneous conductor model developed recently with the assumption of a sinusoidally varying local conductivity in the conducting phase has been successfully applied to analyse the data in this glass system. The Kohlrausch-Williams-Watts (KWW) stretched exponential function has also been used to fit the measured modulus spectra. The exponentβ is found to be correlated to the conductivity fluctuation in the conducting phase as assumed in the heterogeneous model.

    • Synthesis of nanocomposites using glasses and mica as templates

      D Chakravorty S Basu B N Pal P K Mukherjee B Ghosh K Chatterjee A Bose S Bhattacharya A Banerjee

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      Various nanocomposites were synthesized using either a silica-based glass or mica crystallites as the medium. In some cases by an oxidation or a sulfidation treatment a core-shell nanostructure could be generated. Iron–iron oxide core-shell structured nanocomposites exhibited excellent humidity sensing behaviour. Gold–gold sulfide core-shell nanorods exhibited a number of optical absorption peaks which arose because of their structural characteristics. Nanoparticles of silver and silver oxide could be aligned in a polymethylmethacrylate film by an a.c. electric field of 1 MHz frequency. The composites showed large sensitivity to relative humidity. Lead sulfide nanowires of diameter, 1.2 nm, were grown within the nanochannels of Na-4 mica. These exhibited a semiconductor to metal transition at around 300 K. This arose because of high pressure generated on the nanowires. Copper sulfide nanowires grown within the Na-4 mica channels showed metallic behaviour. Silver core–silver orthosilicate shell nanostructures developed within a silicate glass medium showed discontinuous changes in resistivity at some specific temperatures. This was explained as arising due to excitation of Lamb modes at certain pressures generated because of thermal expansion mismatch of the core and the shell phases. Optical properties of iron core–iron oxide shell nanocomposites when analysed by effective medium theory led to the result of a metal non-metal transition for particle diameters below a critical value. Similar results were obtained from optical absorption data of silver nanoparticles grown in a tetrapeptide solution.

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