• A K Bandyopadhyay

      Articles written in Pramana – Journal of Physics

    • Electrical resistivity studies of benzidine-TCNQ and its inclusion compound under high pressure

      A K Bandyopadhyay S V Subramanyam

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      Electrical resistivity studies of the charge transfer complex benzidine—TCNQ and its inclusion compound, have been carried out up to pressures 8 GPa. Two types of behaviour were observed in these complexes under high pressure and this difference is interpreted and discussed.

    • Electrical resistivity studies of certain quasi one-dimensional organic systems at high pressures and low temperatures

      A K Bandyopadhyay

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      We report the electrical resistivity studies of six quasi one-dimensional organic systems under high pressures up to 8 GPa and temperatures down to 77K. The room temperature resistivity of these complexes lies in the wide range from 108 ohm cm to 0.05 ohm cm, but they have common features under high pressures. The possible interpretations of these behaviours have also been discussed.

    • Electrical transport and high pressure studies on bulk Ge20Te80 glass

      G Parthasarathy A K Bandyopadhyay S Asokan E S R Gopal

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      The electrical resistivity of bulk Ge20Te80 has been measured as a function of pressure and temperature. At 5 GPa, an amorphous semiconductor-to-crystalline metal transition has been observed. The sample recovered from the high pressure cell, after the application of 7 GPa, has a face-centred cubic structure with a lattice constant of 6·42 A. In crystalline sample, the semiconductor-to-metal transition occurs at 7 GPa. The thermoelectric power has also been measured for glassy samples in the temperature range 300–240 K.

    • Effect of viscosity of the pressure-transmitting fluid on the metrological characterization of the piston gauge up to 1 GPa

      J K N Sharma A K Bandyopadhyay

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      A systematic theoretical investigation has been carried out to study the effect of viscosity of the pressure-transmitting fluids on the measurement of pressure up to 1 GPa using piston gauges. The fluid flow equation is modified to determine the fall rate (v) with pressure (P), taking the pressure-dependent viscosityη(P) and clearance between piston and cylinder [H(P)] terms into account. Above 0.4 GPa, the fall rate curve shows the tendency to be pressure independent. The near-constancy ofv withP can be avoided with less viscous fluid or by increasingH(P). Finally. the initial clearance obtained from the experimental data of fall rate, shows a weak dependence of pressure, although theoretically it is assumed to be independent of pressure. This weak pressure dependence is attributed to the effect of viscosity of the pressure transmitting fluid.

    • Effect of liquid phase on the triple point pressure of argon

      A K Bandyopadhyay J K N Sharma E S R Gopal

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      We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value ofτ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔPh), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.

    • Establishment of the mercury fixed point around 0°C using volumetric method

      J K N Sharma A K Bandyopadhyay

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      The paper describes the determination of melting pressure of mercury around 0°C using the volume method at the National Physical Laboratory. Also described are the details of the experimental set-up and the estimation of the uncertainty in the measurement of pressure. The equilibrium pressure in the flat region of the melting curve over which bulk transformation occurs, is established by increasing/decreasing the pressure. The scatter in the obtained data for equilibrium pressures is within the limit of experimental uncertainty of the measurement of pressure. The average observed value for the melting pressure of mercury at 0·002°C is 756·93±0·25 MPa agreeing well with the reported value of Dadsonet al [1] and Molinaret al [2a, b].

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