• Volume 44, Issue 5

      May 1995,   pages  397-488

    • Effect of nonlocal elasticity on internal friction peaks observed during martensite transformation

      Ali Doğgan

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      The internal friction associated with martensite is calculated using elastic interaction energy between dislocations and solute atoms in nonlocal elasticity during low temperature aging process. The relaxation strength depends on the lattice parameter of the crystal as well as the temperature and the heating rate. The peak heights increase with increasing lattice parameter. The proposed model can demonstrate more realistically the shape of the change of internal friction versus temperature when nonlocal elasticity is included.

    • Dielectric study of aqueous solution of acetonitrile

      S N Helambe M P Lokhande A C Kumbharkhane S C Mehrotra S Doraiswamy

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      Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous solutions of acetonitrile in temperature range of 0°C to 40°C. The calibration method based on the least squares fit method has been used. The excess permittivity, activation energy, Kirkwood correlation factor and activation energy of acetonitrile-water system have also been determined. The dielectric data show that acetonitrile molecules interact such that the dipoles have a tendency to remain antiparallel.

    • Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

      S Bera R N P Choudhary

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      The polycrystalline samples of Pb(Li1/4Dy1/4W1/2)O3 have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.

    • Phonon properties of rare earth ytterbium pnictides

      Prafulla K Jha Sankar P Sanyal

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      We report for the first time the complete phonon dispersion curves for the ytterbium pnictide compounds (YbN, YbP and YbAs) using a breathing shell model to establish their predominant ionic nature. The calculated results also show that this group of rare earth compounds does not show any elastic and phonon anomalies which are the characteristic features of other rare earth compounds. We emphasize the need for further Raman and neutron scattering measurements.

    • Lattice vibronics of bcc phase metals (Ti, Zr and Hf) at higher temperatures

      S K Saxena R M Agrawal R P S Rathore

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      Ashcroft’s analytic bare ion pseudopotential form factor with a modified Hartree dielectric function has been employed to represent the temperature dependent interionic potential. This potential includes both direct ion-ion interaction and indirect ion-electron-ion interaction with and without the effects of ‘d’ bands, in some scantily studied complexbcc metals vizbcc Ti, Zr and Hf. The ab initio radial and tangential force constants extending out to 15th nearest neighbours are computed for the metals. The said potential is used for predicting the binding energy, elastic constants and phonon dispersion of the above mentioned metals and the results are satisfactorily compared with the corresponding measured data.

    • Temperature variation of electric field gradient in scandium metal

      B B Panigrahi N C Mohapatra

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      Electric field gradient (EFG) in scandium metal has been evaluated at temperatures 11 K and 293 K using band wave functions determined in the temperature dependent model potentials. The results of net EFG obtained are −3.756×1013 esu/cm3 and −8.009×1013esu/cm3 at 11 K and 293 K respectively. The agreement with available experimental result is reasonably good.

    • Composite Anderson-Newns model and chemisorption characteristics of nickel-hydrogen system

      Ravinder Guleria P K Ahluwalia K C Sharma

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      The composite Anderson-Newns model and triangular weighted density of states are used to study the electron density of states, magnetic moment and charge transfer of adatoms for a chemisorbed system. The model has been applied to hydrogen chemisorbed on nickel. It has been observed that with the increase in coverage, number of B-AB states as well as bond strength increases, whereas the magnetic moment and adatom charge decrease with coverage. These results match with the experimental data.

    • Vibrational analysis of NaM2OH(H2O)(MoO4)2/D2O [M=Ni, Zn]

      R Ratheesh G Suresh V U Nayar

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      The infrared and Raman spectra of NaNi2OH(H2O)(MoO4)2 and NaZn2OH (H2O)(MoO4)2 and their partially deuterated analogues are recorded and analysed on the basis of vibrations of MoO42− tetrahedra and H2O molecules. The MoO42− groups are found to be more distorted in NaNi2OH(H2O)(MoO4)2 than in the other compound. Bands indicating the presence of H3O+ ions are not observed in NaZn2OH(H2O)(MoO4)2 ruling out the possibility of the formulation of NaZn2OHO(MoO3OH)2. Hydrogen bonds of medium strength are present in both the compounds.

    • Measurement of cross-section of excitation transfer from 3s2 to 4s1 and 5s1 energy levels of neon

      R K Garg Vasant Dandawate

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      Collision induced non-radiative transitions in neon plasma have been studied using high intra-cavity radiation field of a 633 nm He-Ne laser. The transitions, induced from 3s2 energy level to 4s1 and 5s1 groups of energy levels, have been detected as changes in intensities of the spectral lines originating from these energy levels. From these intensity measurements, the quantities governing the transitions i.e. (i)S3e/S3RT, the ratio of the probabilities of electronic deexcitation to the total radiative deexcitation of energy level 3 (ii) 〈r23eve〉, rate of excitation transfer per particle and (iii)S23e, the total probability for excitation transfer from level 2 to level 3 at a certain value of electron density have been calculated.

    • Fringe formation theory for real-time holographic interferometry using Bi12SiO20

      C S Narayanamurthy

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      A simple theory has been developed to explain the fringe formation in real-time holographic interferometry using BSO (bismuthsiliconoxide) crystal for interferometric applications. Detailed analysis has been given to choose the optimum size of the crystals.

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