Articles written in Pramana – Journal of Physics

    • The infrared spectra of tutton salts 1. A comparative study of (NH4)2 M″(SO4)2·6H2O (M″=Ni, Co or Mg)

      B Singh Shashi P Gupta B N Khanna

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      The infrared spectra of (NH4)2M″(SO4)2.6H2O has been analysed in the region 4000–250 cm−1. The dynamics of each crystal has been discussed in terms of 234 phonon modes, including 3 acoustical ones, using the unit cell approximation. The ambiguity in the assignments of the bands in the region 900–500 cm−1 has been removed by assigning the bands in this region to the libratory modes of H2O molecules. It has been concluded that the NH4+ and SO42− ions have a symmetry lower thanTdand also the complex [M″(H2O)6]2+ has a symmetry lower than Oh. The hydrogen bonding is the strongest in the Ni-salt and the weakest in the Mg-salt.

    • The infrared and laser Raman spectra of K2Zn(SO4)2 · 6H2O

      B Singh Shashi Prabha Gupta B N Khanna

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      The Raman spectra of the single crystal of K2Zn(SO4)2·6H2O belonging toC2h5 space group in the 40–1200 cm−1 region in different scattering geometries and their spectra ofthe microcrystalline salt in the 1500-50 cm−1 region have been reported. The dynamics of the crystal has been described in terms of 186 phonon modes under the unit cell approximation. The weak bands in the region 400–900 cm−1 have been assigned to the libratory modes of H2O molecules in contradiction to the assignments reported by Ananthanarayanan. The ambiguities existing in the literature about the assignments ofν2c andν5c modes of [Zn(H2O)6]2+ have also been removed. The translatory and libratory modes of different units of the crystal have been identified and assignments are made using farir and Raman data on various isomorphous tutton salts.

      It has been inferred that both SO42− tetrahedron and [Zn(H2O)6]2+ octahedron undergo linear as well as angular distortions from their free state symmetries in the crystal.

    • Relationship between torsional frequency and potential barrier height forABn type molecular system

      Y S Jain B Singh B N Khanna

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      A relationship between the torsional frequency (v10) and the potential barrier (Vn) has been determined forABn type molecular system havingn-fold symmetry axis. It is found thatv10 varies prominently asVn1/2,Vn andVn2 in certain ranges. TheVn value computed fromv10 andI*r has been compared with that obtained from other experimental data for someABn units in different molecular-crystalline systems. Although there is in general a good agreement, in some cases the values differ significantly, perhaps due to the erroneous assignment of torsional mode and/or the large errors in theVn value obtained from other experimental data.

    • Collective bounce-off phenomenon in139La+Ag(Br) reaction at 1.1 A GeV energy

      B Singh H S Palsania V Kumar K B Bhalla S Lokanathan

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      Out of a total statistics of 896139La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and84Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionTij) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.

    • Scattering and absorption differential cross sections for double photon Compton scattering

      B S Sandhu M B Saddi B Singh B S Ghumman

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      The scattering and absorption differential cross sections for nonlinear QED process such as double photon Compton scattering have been measured as a function of independent final photon energy. The incident gamma photons are of 0.662 MeV in energy as produced by an 8 Ci137Cs radioactive source and thin aluminum foils are used as scatterer. The two simultaneously emitted photons in this process are detected in coincidence using two Nal(T1) scintillation detectors and a slow-fast coincidence set-up of 30 nsec resolving time. The measured values of scattering and absorption differential cross sections agree with theory within experimental estimated error.

    • Dielectric relaxation and ac conductivity of sodium tungsten phosphate glasses

      B Singh P S Tarsikka L Singh

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      Studies of dielectric relaxation and ac conductivity have been made on three samples of sodium tungsten phosphate glasses over a temperature range of 77–420 K. Complex relative permitivity data have been analyzed using dielectric modulus approach. Conductivity relaxation frequency increases with the increase of temperature. Activation energy for conductivity relaxation has also been evaluated. Measured ac conductivity (σm(ω)) has been found to be higher than σdc at low temperatures whereas at high temperature σm(ω) becomes equal to σdc at all frequencies. The ac conductivity obeys the relation σac(ω)=AωS over a considerable range of low temperatures. Values of exponent S are nearly equal to unity at about 78 K and the values decrease non-linearly with the increase of temperature. Values of the number density of states at Fermi level (N(EF)) have been evaluated at 80 K assuming values of electron wave function decay constant α to be 0.5 (Å)−1. Values of N(EF) have the order 1020 which are well within the range suggested for localized states. Present values of N(EF) are smaller than those for tungsten phosphate glasses.

    • The synthesis and study of structural, optical and electrical behaviours of tin oxide/polyaniline $\rm{(SnO_{2}/PANI)}$ nanocomposites


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      A series of tin oxide $\rm{(SnO_{2})}$/polyaniline (PANI) nanocomposites with loading of different wt% of PANI were synthesised using a solution-based processing method for improving the structural and physical properties of tin oxide. The effect of PANI loading on the gross structure, surface morphology, optical properties and electrical properties of $\rm{(SnO_{2})}$/PANI nanocomposites was investigated. The scanning electron micrographs (SEM) show congruent dispersal of PANI in the tin oxide matrix where the gross/average structure is unchanged as revealed by powder X-ray diffraction (PXRD). A slight change in the lattice parameter of the pristine rutile crystalline structure $\rm{(SnO_{2})}$and its nanocomposites has been recorded. However, the crystallite size has been found to decrease from 60 to 40 nm with different wt% loading of PANI. The presence of characteristic Fourier transform infrared (FT-IR) peaks dovetail to $\rm{C–H, C=C, NH_{2}, C–C}$ and the energy-dispersive analysis of X-rays (EDAX) confirm the development of the PANI nanocomposite. Photoluminescence (PL) spectroscopic study shows the gradual decrement in the intensity of the emission peak at 611 nm due to the disappearance of surface defects associated with oxygen vacancies. The uniform dispersion of PANI at the nanoscale significantly enhanced the electrical properties, e.g. four orders of magnitude changes in electrical conductivity and carrier mobility.

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