Indian Journal of Pure and Applied Physics

http://www.niscair.res.in

 

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VOLUME 40                                                      NUMBER 12                                                  DECEMBER  2002

CODEN:IJOPAU 40(12) 841-944(2002)                                                                                                       ISSN: 0019-5596

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CONTENTS

 

Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics and Fluid Dynamics

Ultrasonic attenuation in semiconductors

      Devraj Singh, R R Yadav* & Arvind Kumar Tiwari

 

845

Excess volume, viscosity and compressibility of binary mixtures consisting of o-chlorophenol,
      o-cresol and m-cresol with n-n-diethyl acetamide at different temperatures

      T Satyanarayana Rao, N Veeraiah & C Rambabu*

 

850

Condensed Matter: Structure, Mechanical and Thermal Properties

Diffused motion in aqueous solutions

      S N Changdar

 

857

Study of ionic conductivity in KBr:CrO4)2-crystals

      G Saibabu, N Vasanth Kumar, A Ramachandra Reddy & D Srikanth

862

Luminescence in divalent impurity activated LiF single crystals

      R S Kher, S J Dhoble*, M S K Khokhar & M Chougaonkar

867

Thermal studies on (Ge0.9Sn0.1Se2)1-x Agx chalcogenide glasses

      L A Wahab

873

Effect of plasmons on supercondcting transition temperature of Ba0.6K0.4BiO3:
      A three square well approach

      Dinesh Varshney*, R P Kumhar, Sanjay Shah & R K Singh


879

Anharmonic apical oxygen vibration in high Tc superconductors

      K M Khanna* & M S Karap Kirui

887

Melting temperature of helium to high pressures

      Kamal Kapoor & Narsingh Dass*

917

Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties

Structural and optical studies of perylene-doped polymer thin films

      S R Pujari*, P N Bhosale, P M R Rao & S R Patil

896

Optical and thermodynamic studies of binary mixtures of nematic liquid crystals from
      homologous members of alkyloxybenzoic acid

      Ravindra Dhar*, R S Pandey & V K Agrawal

 

901

XANES and EXAFS studies of some copper (II) mixed-ligand complexes

      R K Katare, S K Joshi*, B D Shrivastava, R N Patel & A Mishra

908

Mossbauer spectroscopic study of soils collected from Panipat region

      Roshan Lal & N D Sharma*

914

News Scan

Superconductivity instruments

      J B Dhawan

 

919

____________

*The corresponding author has been indicated by (*) mark in case of papers with more than one author

 

 

Indian Journal of Pure & Applied Physics

Vol. 40, December  2002, pp. 845-849

Ultrasonic attenuation in semiconductors

Devraj Singh*, R R Yadav & Arvind Kumar Tiwari

Department of Physics, University of Allahabad, Allahabad 211 002

Received 8 March 2002; accepted 24 September 2002

The ultrasonic phonon-viscosity loss and thermo-elastic loss have been studied in octahedral semiconductors along <100>, <110> and <111> crystallographic directions as a function of high temperature (@ 300K). For this evaluation, the temperature dependence of second- and third-order elastic constants starting with two basic parameters has been computed. The thermo-elastic loss is very small as compared to phonon-viscosity loss. The behaviour of temperature dependence of ultrasonic attenuation is the same as in other semiconducting materials.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 850-856

Excess volume, viscosity and compressibility of binary mixtures consisting of o-chlorophenol, o-cresol and m-cresol with n-n-diethyl acetamide at different temperatures

T Satyanarayana Rao, N Veeraiah & C Rambabu*

Department of Physics, Nagarjuna University PG Centre, Nuzvid, Andhra Pradesh, 521 201

*Department of Chemistry, Nagarjuna University PG Centre, Nuzvid, Andhra Pradesh, 521 201

Received 18 January 2002; accepted 24 September 2002

The densities, viscosities and ultrasonic velocities of binary mixtures of o-chlorophenol, o-cresol, m-cresol with N,N-diethyl acetamide have been determined at 308.15, 313.15, 318.15, 323.15 K over the whole composition-range, using density bottle, ostwald viscometer, and with single crystal ultrasonic pulse echo-interferometer respectively. These data have been utilized to estimate the excess volume (VE), excess viscosity (hE), excess compressibility (KsE), excess inter-molecular free-length, and Grunberg and Nissan parameter d. Values of VE for o-chlorophenol + N,N-diethyl acetamide system and m-cresol + N,N-diethyl acetamide system are negative at all temperatures but, for o-cresol + N-N diethyl acetamide VE values are positive at lower mole fraction of o-cresol and increase with increase in temperature. hE values are positive for all the systems and the magnitude of hE decreases with increase of temperature in all cases. KsE values are negative for all the systems over the whole composition-range. Analysis of these suggests the absence of any strong specific interactions.

Indian J Pure & Applied Physics

Vol. 40, December  2002, pp. 857-861

Diffusive motion in aqueous solutions

S N Changdar

Physics Department, Bose Institute, Kolkata

Received 8 August 2001; accepted 11 September 2002

The interest in diffusion phenomena arises from both applied and fundamental points of view and in recent years, there has been some spectacular development in this study both theoretically and experimentally. Inelastic neutron scattering, NMR, optical and above all radioactive tracer techniques have accumulated important information about the migration of ions, or molecules through a maze of molecules. The difficulty in the study of liquids lies in the fact that, kinetic energy and potential energy of the constituent particles in a liquid are comparable and both must be taken into account to calculate any property, which is to be compared with observed results. In general, by employing techniques which increase the thermal motion of the constituent particles or by varying the composition of the binary and ternary systems, much information can be gathered about liquids and, in this respect, diffusion study in liquids is an important tool. It is very interesting and very important to observe the change in diffusion coefficient in some aqueous solution with the introduction of known amounts of some other salts or acids. This study of coupled flow has been undertaken by several groups of workers. A sliding cell method based on radioactive tracer technique has been developed in the laboratory of the author and it has been used to measure diffusion coefficient in H3PO4-H2O system containing different amount of salts of this weak acid. Different radioactive isotopes like Na-22, Na-24, Hg-203, Ga-72, Cs-134, Cs-137, Tl-204, P-32 etc., have been used in the laboratory for diffusion measurements in different systems. Irreversible thermodynamical principles have been applied to explain the observed results. Both H2O and D2O have been employed as solvents and the breaking of their structures with the introduction of salts have been explained.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 862-866

Study of ionic conductivity in KBr: (CrO4)2- crystals

G Saibabu1, N Vasanth Kumar2, A Ramachandra Reddy3 & D Srikanth3

1Department of Physics, Railway Junior College, Kazipet, Warangal 506 003

2Bharath Sanchar Nigam Limited, Warangal

3Department of Physics, Regional Engineering College, Warangal 506 009

Received 12 April 2002; revised 6 August 2002

The ionic conductivity of pure KBr and KBr crystals doped with chromate anion has been measured in the temperature range of 200–600 °C. In pure KBr crystals, large contribution to conductivity by cation vacancies has been observed at higher temperatures. Ionic conductivity measurements are made on pure KBr crystals and KBr crystals doped with 0.25, 0.5 and 0.75 mole % of chromate anion in as-grown state. Further, the effects of quenching and annealing on conductivity of KBr crystals doped with 0.75 mole % chromate ion are measured. The conductivity versus temperature plots show that, as concentration of impurity anions increases, the conductivity decreases in extrinsic associated region. As the concentration increases to 0.75 mole %, the conductivity increased to high value compared to 0.5 mole %. But, it is less than that of pure crystals. The extrinsic un-associated region shows a slight variation in conductivity but, tends to be same that of as-grown pure KBr crystals. The variation in conductivity of doped KBr crystals are explained on the basis of formation of complexes with background impurities, formation of neutral pairs, introduction of fresh dislocations, etc. The variation in conductivity due to quenching and annealing is explained on the basis of dissociations and aggregation of complexes, vanishing of newly introduced dislocations, etc. The corresponding activation energy values are evaluated.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 867-872

Luminescence in divalent impurity activated LiF single crystals

R S Kher, S J Dhoble*, M S K Khokhar** & M Chougaonkar***

Department of Physics, Government Autonomous PG Science College, Bilaspur 495 001

*Kamla Nehru College, Sakkardara Square, Nagpur 440 009

**Guru Ghasidas University, Bilaspur 495 009

***Environmental Assessment Division, Bhabha Atomic Research Centre, Mumbai 400 085

Received 21 January 2002; revised 9 August 2002; accepted

LiF single crystals doped with varying concentrations of Ba, Sr and Ca have been grown by Bridgman technique and their thermo-luminescence (TL) and TL emission spectrum induced by g-irradiation at room temperature for doses between 103 to 105 R have been recorded. In the TL glow curves, peaks around 380, 425 and 500 K are produced irrespective of the impurity added, but, the relative intensity of these glow peaks varies for different dopants. At low g-exposure the TL efficiency increases with decrease in the ionic radius of the dopant. The dependence of various TL peaks on g-exposure shows that, low temperature peaks have got their optimum intensity as compared to high temperature TL peaks.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 873-878

Thermal studies on (Ge0.9Sn0.1Se2)1-xAgx chalcogenide glasses

L A Wahab

National Centre for Radiation Research & Technology, Cairo, Egypt

Received 29 May 2002; accepted 17 October 2002

The effect of silver on the phenomena accompanying the thermally induced structural changes in Ge0.9Sn0.1Se2 chalcogenide glass has been investigated using DSC measurements. Glass stability and kinetic resistance to crystallization are shown in terms of glass forming tendency (Kgl), crystallization enthalpy (DHc) and crystallization energy (E). Studies of the crystallization kinetics using the isothermal and non-isothermal single scan techniques shows that, random nuclei are already present in as-quenched alloys and growth occurred in two dimensions.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 879-886

Effect of plasmons on superconducting transition temperature of Ba0.6K0.4BiO3: A three square well approach

Dinesh Varshney*, R P Kumhar*, Sanjay Shah† & R K Singh‡

*School of Physics, Vigyan Bhawan, Devi Ahilya University, Khandwa Road Campus, Indore 452 017

†Department of Physics, PMB Gujarati Science College, Devi Ahilya University, Indore 452 001

‡School of Pure and Applied Physics, Guru Ghasidas University, Bilaspur 495 009

Received 12 June 2001; revised December 2001; accepted 29 April 2002

By assuming the existence of a low energy plasmon in attractive interaction, the cooper pairing theory is extended for cubic perovskite Ba0.6K0.4BiO3. Three square well model for the three interactions namely, electron-phonon, electron-plasmon and Coulomb in the calculation of superconducting transition temperature (Tc) has been employed. The analytical solutions for the energy gap equation allow one to visualise the relative interplay of various interactions. To correlate the Tc with various coupling strengths (lph, lpl and m*)  curves of Tc are presented with them. The values of the coupling strength and of the Coulomb interaction parameter indicate that, the superconductor is in the intermediate coupling regime. The superconducting transition temperature of optimally doped Ba-K-BiO is estimated as 25 K, for lph » 0.6, lpl » 0.1 and m* » 0.18. The low energy plasmons play a key role in raising Tc with the increased lpl values. The present analysis points to the importance of both plasmons and optical phonons in determining the effective electron-electron interaction leading to superconductivity in doped cubic perovskites.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 887-895

Anharmonic apical oxygen vibration in high-Tc superconductors

K M Khanna & M S Karap Kirui

Physics Department, Moi University, Box 3900, Eldoret, Kenya

Received 29 March 2001; accepted 11 April 2002

Using time-independent perturbation theory, a theoretical calculation has been performed for the transition temperatures for various high-Tc oxide compounds. It has been assumed that, three electrons are responsible for the superconducting current. Whereas two of these electrons form an exotic bound pair, the third electron causes perturbation  with respect to apical oxygen vibrations. From the calculations, the transition temperatures are found to be realistic and comparable with experimental results.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 917-918

NOTE

Melting temperature of helium to high pressures

Kamal Kapoor & Narsingh Dass

Physics Department, College of Engineering Roorkee,
Roorkee 247 667

Received 13 November 2001; revised 18 March 2002;
accepted 24 September 2002

The melting temperature, Tm, is calculated in the pressure range of 0.2-185.0 kbars in case of helium. The results so obtained are compared with the available data. The agreement is very good in the whole pressure range of present study. Further, the pressure corresponding to the melting maximum in helium is found to be 17800 kbars.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 896-900

Structural and optical studies of perylene-doped polymer thin films

S R Pujari, P N Bhosale, P M R Rao* & S R Patil

Fluorescence Spectroscopy Laboratory, Chemistry Department, Shivaji University, Kolhapur 416 004

*Spectroscopy Division, Bhabha Atomic Research Centre, Mumbai

Received 8 March 2002; revised 9 September 2002; accepted 24 September 2002

Thin films of perylene in polystyrene matrix have been prepared by spin coating technique. The concentration of polystyrene is kept constant to 1 wt% while that of perylene dopant varied in the range 1΄10-5-1΄10-1 wt%. The thickness of the films depends upon the concentration of perylene and varies from 45.48 to 582.16 nm. The structural aspects of the films were studied by recording the X-ray diffractogram of the films. The results of X-ray diffraction analysis reveal the crystalline nature of the film. The optical properties were studied by recording absorption, excitation and fluorescence spectra. The band gap energy of perylene in polymer films was calculated from absorption curves. The fluorescence spectra of the films show monomeric as well as dimeric emission bands. The films with lower concentration of perylene show monomeric emission similar to that of dilute solution, while the films with higher concentration of perylene exhibit structure-less broad emission. These emission bands appeared at 509 and 525 nm are attributed as arising from dimmer, formed in the ground-state by parallel orientational alignment of neighbouring molecules. The additional bands observed in the blue region of the absorption and excitation spectra of the films containing higher concentration of perylene confirm the formation of ground-state dimer.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 901-907

Optical and thermodynamic studies of binary mixtures of
nematic liquid crystals from 
homologous members of alkyloxybenzoic acid

Ravindra Dhar† & R S Pandey

Physics Department, Ewing Christian College, Allahabad 211 003

and

V K Agrawal

Physics Department, Allahabad University, Allahabad 211 002

Received 20 March 2002; revised 17 June 2002; accepted 6 August 2002

Transition temperature (TP), transition enthalpy (DH) and transition entropy (DS) for the binary mixtures of heptyloxybenzoic acid (HOBA) and decyloxybenzoic acid (DOBA) in different mole ratios have been determined using differential scanning calorimeter (DSC). The phase diagrams for the heating and cooling cycles have been drawn which show the eutectic composition of DOBA-HOBA binary system in the ratio of 48:52 mole per cent. A wide range smectic C (SmC) phase (range ~40 °C) followed by the nematic (N) phase (range ~34 °C) has been observed around the eutectic composition of DOBA-HOBA binary system. SmC-N and N-I (isotropic) transition temperatures (TC-N and TN-I) have been found to vary, almost linearly, with the mole fraction of components, indicating the system as an ideal mixture. For the eutectic composition of the HOBA-DOBA system, it has been possible to bring down SmC phase to 60 °C with enhanced temperature range, whereas no member of the alkyloxybenzoic acid series has SmC phase below 92 °C.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 908-913

XANES and EXAFS studies of some
copper (II) mixed-ligand complexes

R K Katare1, S K Joshi1*, B D Shrivastava2, R N Patel3 & A Mishra4

1Physics Department, Government Post-Graduate Arts and Science College, Ratlam 457 001

2School of Studies in Physics, Vikram University, Ujjain 456 010

3Department of Chemistry, APS University, Rewa 486 003

4School of Physics, Devi Ahilya University, Indore 452 017

Received 10 August 2001, accepted 20 August 2002

X-ray K-absorption spectroscopic studies have been carried out on four copper (II) mixed-ligand complexes. The complexes are: I-[Cu(asp)(H2O)2], II-[Cu(asp)(imh)].2H2O, III-[Cu(asp)(py)], IV-[Cu(asp)(bz-imH)].2 H2O, in which aspartic acid has been used as primary ligand and water (H2O), imidazole (imH), pyridine (py) and benzimidazole (bz-imH) have been used as secondary ligands. Various X-ray absorption parameters e.g., chemical shift, edge-width and shift of the principal absorption maximum have been obtained in the present study. These parameters have been utilized to explain the nature of bonding and structure of the complexes. Further, the observed chemical shifts have been correlated with percentage covalency in these complexes. Average metal-ligand bond distances have also been estimated using EXAFS data. The studies establish significant correlation between various parameters for these complexes.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 914-918

Mossbauer spectroscopic study of soils collected
from Panipat region

Roshan Lal & N D Sharma

Department of Physics, Kurukshetra University, Kurukshetra. 136 119

Received 2 July 2002; revised 16 October 2002; accepted

Mossbauer spectroscopy of 57Fe has been used to study some soil samples picked up from regions where the growth of crops is not normal as well as from the fertile part of the land in the Panipat district of Haryana. The ferrous-ferric ratios in these samples were determined. An attempt has also been made to correlate the Fe2+/Fe3+ ratio with pH values of the samples. The importance of these results lies in the necessity of application of suitable micronutrients in the area where the growth of crops is below normal.

Indian Journal of Pure & Applied Physics

Vol. 40, December 2002, pp. 919-920

NEWS SCAN

Superconducting instruments

Magnetism is known for ages although, until around 1820, the only magnets available were naturally occurring rocks called lodestones (magnetite). The word magnetism arose from Magnesia in Asia Minor, where lodestones were first found. Total magnetic field strength was first measured in gauss (G), but most measurements are now given in the much larger units of tesla (1T=10+G). To put the strength of fields produced by superconducting magnets into perspective, Earth’s relatively weak field averages 0.5 G, and a standard bar magnet produces a magnetic field strength of approximately 3,000 G (0.3 T) at its poles. A significant understanding of superconductivity and how to harness this phenomenon has emerged over the past 40 years from many laboratories.