Indian Journal of Pure and Applied Physics

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Volume 46

Number 7

JULY 2008

CODEN: IJOPAU 46 (7) 459-530

                                                                        ISSN: 0019-5596

 

 

 

CONTENTS

 

Atomic and Molecular Physics

 

Discharge conditions and emission spectroscopy of N2 and N2+ active species in a variable power dc pulsed plasma used for steel nitriding

463

M K Sharma* & B K Saikia

 

Physics of Gases, Plasmas and Electric Discharges

 

Transverse acceleration of ions in cusp: Electrostatic ion-cyclotron instability with general loss-cone distribution as a possible source

471

Ruchi Mishra, P Varma & M S Tiwari *

 

Condensed Matter: Structural, Mechanical and Thermal Properties

 

Effect of horizontal thermal gradient on ferroconvection

477

G Vaidyanathan* , R Sekar & R Hemalatha

 

Structural, magnetic and magnetoresistance properties of La0.88Ca0.12MnO3 single crystals

484

Ashish Bodhaye, Sankar P Sanyal*, & Ya M Mukovskii

 

X-ray diffraction studies of tungsten substituted molybdenum disulphide

488

Atul K Shah & P N Gajjar*

 

Investigations of thermally stimulated polarization current in polyetherimide

491

Randhir Singh*, B K Kaushik & J K Quamara

 

Stability and phase transition in Al65Cu20Co15-XFeX (0£x£15) quasi-crystalline systems

497

K Singh & D Bahadur*

 

Analysis of optoelectronic properties of ANB8-N type binary solids

502

B P Singh*, S Tripti & Vipnesh Singh

 

Growth and characterization of struvite crystals

507

Chetan K Chauhan, K C  Joseph, B B  Parekh & M J  Joshi*

 

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

 

Ionic conduction and dielectric dispersion study on chain dynamics of poly(vinyl pyrrolidone) –glycerol blends

513

R J Sengwa* & Sonu Sankhla

 

Dielectric dispersion and relaxation of mixtures of 1-propanol and phenol at lower microwave frequencies

521

A D Vyas*, V A Rana, S P Bhatnagar & V M Vashisth

 

 

 

___________

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

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 463-470

 

Discharge conditions and emission spectroscopy of N2 and N2+ active species in a variable power dc pulsed plasma used for steel nitriding

M K Sharma* & B K Saikia

Centre of Plasma Physics, Tepesia, Sonapur, Guwahati, Assam 782 402

Received 5 January 2007; accepted 14 February 2008

The variations of stainless steel cathode temperature (Tc) as a function of nominal plasma power (driven by discharge frequency) and duty cycle at different pressures (0.6-3.2 torr) in nitrogen plasma are reported in conditions favourable for plasma nitriding. Above power at 200 kHz, it is found that increase in power does not have any significant effect on Tc. Corresponding optical emission spectroscopy (OES) study near the cathode surface shows that the presence of vibrational bands of second positive system of N2 (∆v = 0, -1, -2, -3) and first negative system of N2+ (∆v = 0, -1, -2) are dominant. The variation of intensity of those nitrogen molecular bands as a function of discharge power at various pressures has been studied. At 2 torr, the vibrational temperature of N2 molecule is calculated from N2 vibrational spectra at different discharge power regime as frequency is varied from 100 to 500 kHz. The variation of power in this frequency range 50-500 kHz has a similar effect on Tc and optical emission intensity. Floating potential in variable power conditions has been measured by Langmuir probe which shows a plateau after 3.2 Watt/cm2 (at 200 kHz) plasma power density.

Keywords: Plasma power, Discharge frequency, Optical emission spectroscopy, Vibrational bands, Floating potential

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 471-476

 

Transverse acceleration of ions in cusp: Electrostatic ion-cyclotron instability with general loss-cone distribution as a possible source

Ruchi Mishra,  P Varma & M S Tiwari*

Department of Physics, Dr H S Gour Vishwavidyalaya, Sagar (MP) 470 003

Received 21 May 2007; revised 3 January 2008; accepted 2 May 2008

Expressions for the dispersion relation, transverse and parallel energy of the resonant ions and growth rate of the Electrostatic Ion-Cyclotron Instability (EICI) are derived in the presence of the general loss-cone distribution function. The results are interpreted for the space plasma parameters appropriate to the auroral acceleration region. The results of the present study have shown that in the presence of the general loss-cone distribution the growth rate of the EICI enhances at lower perpendicular perturbations. The frequency of the EICI obtained is in accordance with the reported values. In the presence of the loss-cone distribution function, the transverse energy of resonant ions is also enhanced which may then give rise to the observed transverse acceleration of ions in the cusp region.

Keywords: Transverse acceleration of ions, Cusp region, Electrostatic ion-cyclotron instability, Wave-particle interaction

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 477-483

Effect of horizontal thermal gradient on ferroconvection

G Vaidyanathana, R Sekarb  &  R Hemalathac,*

aDepartment of Physics, bDepartment of Mathematics, Pondicherry Engineering College, Puducherry 605 014

cDepartment of Mathematics, Kanchi Mamunivar Centre for Post Graduate Studies, Puducherry 605 008

*E-mail: hemalatha53@yahoo.co.in

Received 3 September 2007; revised 1 April 2008; accepted 12 May 2008

The effect of horizontal thermal gradient on ferro convective instability of a single component system subjected to two dimensional magnetic field has been studied. The fluid layer is assumed to be bounded by free boundaries. The exact solution of constitutive equation is derived using linear theory. Wide range of values of the ratio of horizontal and vertical temperature gradient have been considered. Normally, the magnetization parameter M1 is very large and is taken to be 1000. The system is found to stabilize through stationary mode only. It has also been seen that the oscillatory instability is not possible.

Keywords: Horizontal gradient, Two dimensional heating, Magnetic field, Ferrofluid, Linear theory, Stationary mode

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 484-487

Structural, magnetic and magneto-resistance properties of
La0.88Ca0.12MnO3 single crystals

Ashish Bodhaye1,*, Sankar P Sanyal1 & Ya M Mukovskii2

1Department of Physics, Barkatullah University, Bhopal 462 026

2Moscow State Steel and Alloys Institute, Moscow 117936, Russia

*E-mail: ashish77kumar@gmail.com

Received 28 October 2007; revised 15 April 2008; accepted 22 April 2008

La0.88Ca0.12MnO3 single crystals of high quality have been prepared by using floating zone technique. Their composition and structure are verified using X-ray diffraction and EDAX. The temperature dependence of the resistance along ab-plane and c-axis has been measured in the temperature range 77 K to room temperature in the magnetic fields up to 8 T. The R-T data along ab-plane and c-axis shows a similar behaviour and it is the characteristics of insulating behaviour having the resistance 0.7 MW at 90 K and 16.1 W at 300 K. The insulating behaviour persists under the magnetic field up to H = 8 T. There is no resistance peak or electronic transition over the whole temperature range studied. However, there is a notable change of resistance at about 120 K, seemingly related to paramagnetic insulator to ferromagnetic insulator transition and is confirmed by magnetization measurement transition at a temperature Tc = 122 K. The sharp peak around the same temperature in the heat capacity measurement indicates the onset of long range ordering. The magnetoresistance measured at different magnetic fields shows similar kind of behaviour with some marginal change in the magnitude along ab-plane and c-axis.

Keywords: CMR, La0.88Ca0.12MnO3 single crystal, Ferromagnetic - paramagnetic transition, Magneto-resistance

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 488-490

X-ray diffraction studies of tungsten substituted molybdenum disulphide

Atul K Shah & P N Gajjar*

Sheth R. A. Bhavan’s Science College, Khanpur, Ahmedabad, 380 001, *Department of Physics, University School of Sciences
Gujarat University, Ahmedabad 380 009

Received 1 March 2006; revised 8 January 2008; accepted 16 April 2008

Transition metal dichalcogenide single crystals of tungsten substituted molybdenum disulphide have been grown by chemical vapour transport technique using iodine as transporting agent and direct vapour transport technique. The composition of grown crystals was confirmed on the basis of energy dispersive analysis of X-ray (EDAX) and remaining structural characterization was determined by X-ray diffraction (XRD). The growth condition, growth mechanism and lattice parameters are also determined and presented in the paper.

Keywords: X-ray diffraction, Molybdenum disulphide, Single crystals, EDAX

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 491-496

Investigation of thermally stimulated polarization current in polyetherimide

Randhir Singh*, B K Kaushik & J K Quamara**

Department of Physics, National Institute of Technology, Kurukshetra 136 119

**E-mail: jkquamara@yahoo.com

Received 9 October 2007; revised 28 March 2008 accepted 6 May 2008

Thermally stimulated polarization currents (TSPC) have been investigated in polyetherimide (PEI) in the temperature region 10°-200°C under various polarizing fields, ranging from 12-176 kV/cm with different heating rates. The TSPC spectra show a pronounced peak (P1) around 25°-30°C and a shoulder peak (P2) in certain cases around 90°-110°C attributed to the dipolar nature of ether linkages and carbonyl groups (>C=O), respectively. A steady rise in current is observed beyond 120°C due to the dominance of large conduction currents. During successive cooling, the current retains its positive polarity and peak P2 is observed around 110°C. The peak P1 disappears during second TSPC cycle owing to the temperature dependence of saturation polarization, confirming the dipolar nature of this peak. In few cases the corresponding thermally stimulated depolarization current (TSDC) characteristics have also been recorded, which are found to consist of two peaks P1 and P′2 located around 20° and 160°C, respectively. The peak P1 is consistent with the TSPC peak observed around 25°-30°C whereas peak P′2 corresponds to αβ-relaxation. The thermal variation of dielectric constant of PEI has also been deduced from the TSPC spectra. The experimental observations are in general agreement with the theoretical predictions.

Keywords: Polarization current, Polyetherimide, Thermally stimulated polarization currents

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 497-501

 

Stability and phase transition in Al65Cu20Co15-xFex (0£x£15)
quasi-crystalline systems

 

K Singh & D Bahadur*

School of Physics and Materials Science, Thapar University, Patiala 147 001

*Department of Metallurgical Engineering and Materials Science
Indian Institute of Technology, Mumbai 400 076

E-mail: kusingh@tiet.ac.in

Received 9 August 2007; revised 12 March 2008; accepted 30 April 2008

The samples Al65Cu20Co15-xFex (0£x£15), Al63Cu25Fe12 and Al60Cu20Fe15Si5 have been synthesized. Their stability and formed phases are investigated using differential thermal analysis (DTA) and X-ray diffraction (XRD), respectively. The maximum stability in alloys is found when the Fermi wave vector, kF satisfies the relation KP = 2kF. Apart from this, specific range of e/a (electron per atom) and atomic size ratio of constituents also play an important role in forming the thermodynamically stable quasicrystals.

Keywords: Quasicrystals, X-ray diffraction, Differential thermal analysis, Fermi wave vector

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 502-506

 

Analysis of optoelectronic properties of ANB8-N type binary solids

B P Singh, S Tripti & Vipnesh Singh

Department of Physics, Institute of Basic Sciences, Khandari, Agra 282 002

E-mail: drbps.ibs@gmail.com

Received 16 March 2007; revised 14 March 2008; accepted 28 April 2008

The dependence of refractive index for I-VII, II-VI, III-V semiconductors including alkali halides on the energy band gap and the optical electronegativity difference has been studied. The relationships have been established for estimating the refractive index of materials. In addition, an interrelation between the energy band gap, polarizability and magnetic susceptibility has also been investigated. The computed values of the parameters are then compared with the literature values.

 Keywords: Energy gap, Refractive index, Electronic polarizability, Magnetic susceptibility

 

Indian Journal of Pure & Applied Physics

Vol 46, July 2008, pp. 507-512

 

Growth and characterization of struvite crystals

Chetan K Chauhan, K C Joseph, B B Parekh# & M J Joshi*

Crystal Growth Laboratory, Department of Physics, Saurashtra University, Rajkot 360 005 (Gujarat)

*E-mail: mshilp24@rediffmail.com

Received 2 August 2006; revised 6 December 2007; accepted 17 January 2008

Struvite or ammonium magnesium phosphate hexahydrate (AMP) containing urinary stones are infection stones associated with urea splitting organisms, which are more common in women. Struvite crystals having different morphologies were grown by single diffusion gel growth technique in silica gel. The crystals were characterized by powder XRD, FT-IR, TGA and dielectric study. Kinetic and thermodynamic parameters were evaluated from thermogram. Dielectric study showed that the value of dielectric constant is found to decrease as the frequency increased. The ac resistivity and ac conductivity were also evaluated at different frequency.

Keywords: Struvite crystals, Crystal growth, FT-IR, Thermal study, Kinetic and thermodynamic parameters, Dielectric study

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 513-520

 

Ionic conduction and dielectric dispersion study on chain dynamics of
poly(vinyl pyrrolidone)–glycerol blends

R J Sengwa* & Sonu Sankhla

Dielectric Research Laboratory, Department of Physics, J N V University, Jodhpur 342 005, Rajasthan

E-mail: rjsengwa@rediffmail.com

Received 6 February 2007; revised 10 January 2008; accepted 1 May 2008

Dielectric behaviour of glass-former polymer blends i.e. poly(vinyl pyrrolidone) (PVP) (average molecular weight Mw= 24000, 40000 and 360000 g mol-1) with glycerol (Gly) up to 30 wt % PVP has been investigated in the frequency range 20 Hz-1 MHz at 25oC. The frequency dependent complex dielectric constant of the PVP-Gly blends indicates the relaxation process caused by the micro-Brownian chain motion of the PVP in the frequency range 10 kHz-1 MHz. The values of dielectric relaxation strength and relaxation time for this process were determined to explore the concentration and chain length effect on the relaxation process. The ac conductivity values were found corresponding to dc conductivity at frequencies lower than 10 kHz. The loss part of electric modulus exhibits a peak in the frequency range 10 kHz - 40 kHz, which corresponds to the ionic conductivity relaxation. The complex impedance plane plots of PVP-Gly blends confirm the contribution of the electrode surface polarization effect on the dielectric constant values at frequencies lower than 200 Hz. Further, the results of the dielectric dispersion of the PVP–Gly blends were compared with the dielectric dispersion of poly(vinyl pyrrolidone)–ethylene glycol oligomers (PVP–EGOs) blends [Shinyashiki et al., 2006] to confirm the effect of number of hydroxyl groups of the solvent molecules on the heterogeneous hydrogen bond complex formation in these blends.

Keywords: Poly(vinyl pyrrolidone)-glycerol blends, Chain dynamics, Dielectric constant, Dielectric relaxation time, Electrical conductivity

 

 

Indian Journal of Pure & Applied Physics

Vol. 46, July 2008, pp. 521-525

 

 

Dielectric dispersion and relaxation of mixtures of 1-propanol and phenol at lower microwave frequencies

A D Vyas*, V A Rana*, S P Bhatnagar** & V M Vashisth***

* Department of Physics, School of Sciences, Gujarat University, Ahmedabad

** Department of Physics, Bhavnagar University, Bhavnagar

*** Department of Physics, R A Bhavan’s College, Ahmedabad

* E-mail: ranava2001@yahoo.com

Received 28 March 2007 ; revised 8 August 2007; accepted 11 April 2008

Complex permittivity of 1-propanol, phenol and mixtures of 1-propanol + phenol over wide range of concentration are measured over the frequency range 30MHz to 3.0 GHz using Vector Network Analyzer (VNA). Open ended co-axial probe technique suggested by Wei and Sridhar [Rev Sci Instr, 60 (9) (1989) 304] is used to obtain dielectric constant. The measured values of Î and Î are fitted to Debye equation to obtain dielectric parameters. Obtained values of relaxation time of liquid mixtures are plotted against the concentration of one of the components of the liquid mixtures. Non-linear variation of relaxation time with concentration has been interpreted in terms of molecular interaction among the molecular species of different kinds in liquid mixtures.

Keywords: Complex permittivity, Relaxation time, Molecular interaction, Vector network analyzer