• Volume 50, Issue 3

      March 1998,   pages  205-269

    • A computer simulation study of ionic conductivity in polymer electrolytes

      Aninda Jiban Bhattacharyya T R Middya S Tarafdar

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      In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganization of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH4I and PEO-NH4SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.

    • Spectroscopic study ofβ-Ni(OH)2 under pressure

      Chitra Murli V Sugandhi Nandini Garg Surinder M Sharma S K Sikka

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      Infrared absorption and Raman study ofβ-Ni(OH)2 has been carried out up to 25 GPa and 33 GPa, respectively. The frequency ofA2u internal antisymmetric stretching O-H mode decreases linearly with pressure at a rate of −0.7 cm1/GPa. The FWHM of this mode increases continuously with pressure and reaches a value of ∼ 120 cm−1 around 25 GPa. There was no discernible change observed in the frequency and width of the symmetric stretchingA1g O-H Raman mode up to 33 GPa. The constancy of the Raman mode is taken as a signature of the repulsion produced by H-H contacts in this material under pressure. Lack of any discontinuity in these modes suggests that there is no phase transition in this material in the measured pressure range.

    • Studies on the electrical conductivity, optical absorption and x-ray diffraction in bismuth thin film

      K Jayachandran C S Menon

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      Spectroscopically pure bismuth is evaporated onto glass substrates at different substrate temperature using a Hind Hivac coating plant. The electrical conductivity of bismuth thin films, prepared at different substrate temperatures is measured and thermal activation energy is evaluated. From the recorded optical absorption spectrum in the ultraviolet and visible regions optical band gapEg is determined. X-ray diffractograms are recorded and lattice parameters are determined.

    • Hyperfine interaction study of electric field gradient in hafnium phosphide using181Ta probe

      Vivek Mandot S N A Jaaffrey S S Sharma J Varma

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      The hyperfine interaction of181Ta in HfP has been investigated by time differential perturbed angular correlation method which yielded interaction frequencyvQ=630.20(15) MHz. The observed electric field gradient is calculated to be 1.66(25) × 1020 V/m2.

    • Mean lifetime measurements of F II and F III levels using beam-foil technique

      B N Raja Sekhar S Padmanabhan Aparna Shastri P Meenakshi Raja Rao M B Kurup K G Prasad

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      Beam-foil spectrum of fluorine was recorded in the wavelength region of 2000–4500 Å using F+ ion beams of energies ranging from 216 to 296 KeV. Some of the spectral lines of fluorine observed during the present investigation are hitherto unknown. Mean lifetimes of a few of the excited levels of F II and F III are reported for the first time.

    • Third harmonic generation in layered media in presence of optical bistability of the fundamental

      Jolly Jose S Dutta Gupta

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      We study third harmonic generation in layered configuration when the fundamental exhibits bistable response. We consider two geometries, namely, a Fabry-Perot cavity with reflection coatings and a distributed feedback structure with alternate nonlinear layers. In both the cases for suitable choice of frequency, the power response at the fundamental frequency is bistable. We show that bistability of the fundamental leads to a multivalued character of the generated third harmonic in both the forward and backward directions. Moreover, we study frequency response in the case of the Fabry-Perot cavity and show that additional structures arise in the generated third harmonic due to frequency bistability of the fundamental. Our calculations suggest the possibility of an all optical switch at third harmonic frequency controlled by the parameters (like intensity, frequency) of the fundamental.

    • Generation of squeezed atomic states in cavity QED

      Aditi Ray R R Puri

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      A squeezed atomic state is that state of a system of two-level atoms for which the intrinsic quantum noise in a process of measurement is less than the minimum noise obtained by using a spin coherent state. It is shown that such a state is generated in certain time intervals when a non-squeezed atomic state evolves on interaction with a single mode coherent field inside a lossless cavity. The atoms are assumed to undergo one-photon or two-photon transitions between the given two levels. The maximum atomic squeezing is found as a function of the number of atoms and the field strength. The effect of the field-dependent Stark shift is investigated in the case of the atoms undergoing two-photon transitions.

    • Proton NMR in CeNiInH0.53 down to liquid helium temperature

      R Ray A Ghoshray K Ghoshray N Chatterjee

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      The NMR probe and the matching network has been designed for the1H NMR study in CeNiInH0.53 down to liquid helium temperature using Bruker MSL 100 spectrometer. NMR line-shape measurement shows the absence of any signature of proton pairing in CeNiInH0.53 down to 3.86 K, as it was observed for high hydrogen concentration. The measurement of the spin-lattice relaxation time in the temperature range 300–20K reveals that the relaxation rate is mainly governed by the Korringa-type relaxation mechanism.

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