Navil Kumar, R; Dr.Girijavallabhan,C P(Cochin University Of Science And Technology, June 28, 1989)
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Abstract:
In the present thesis a series of exhaustive
investigations have been carried out on a number of crystalline
samples with special reference tx> the jphase transitions
exhibited by them. These include single crystals
of pure, doped or deuterated specimens of certain ammonium
containing crystals viz., (NH )34H(SO4)2, (NH4)2HPO4,
(NH4)2Cr2O7 znui NH4H2PO4. ac/dc electrical conductivity,
dielectric constant, ionic thermocurrent as wwifil as photoacoustic
measurements have been carried out on most of
them over a wide range of temperature. In addition investigations
have been carried out in pure and doped single
crystals of NaClO3 and NaNO3 using ionic thermocurrent
measurements and these are presented here. Special attention
has been paid to reveal the mechanism of electrical conduction
in various phases of "these crystals and to evaluate
the different parameters involved in the conduction as well
as phase transition process.
The thesis contains ten chapters ‘
Description:
Department of Physics, Cochin
University of Science and Technology
Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by
12 pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at
13 different pressures. These heterojunctions were found to be rectifying with a
14 maximum forward-to-reverse current ratio of about 1,000 in the applied
15 voltage range of -5 V to +5 V. The turn-on voltage of the heterojunctions was
16 found to depend on the ambient oxygen pressure during the growth of the ZnO
17 film. The current density–voltage characteristics and the variation of the
18 series resistance of the n-ZnO/p-Si heterojunctions were found to be in line
19 with the Anderson model and Burstein-Moss (BM) shift.
Syamaprasad, U; Vallabhan, C P G(Elsevier, May , 1981)
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Abstract:
Anomalous variations of d.c. electrical conductivity with temperature are observed in ammonium sulphate single crystals, suggesting a possible phase transition at 150°C. Measurements of thermally stimulated current also support these results. The mechanism of electrical conduction is explained on the basis of studies made on doped and quenched crystals.
Navil Kumar, R; Vallabhan, C P G(IOP Publishing, 1989)
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Abstract:
DC and AC electrical conductivity measurements in single crystals of diammonium hydrogen phosphate along the c axis show anomalous variations at 174, 246 and 416 K. The low-frequency dielectric constant also exhibits peaks exactly at these temperatures with a thermal hysteresis of 13 degrees C for the peak at 416 K. These specific features of the electrical properties are in agreement with earlier NMR second-moment data and can be identified with three distinct phase transitions that occur in the crystal. The electrical conductivity values have been found to increase linearly with impurity concentration in specimens doped with a specific amount of SO42- ions. The mechanisms of the phase transition and of the electrical conduction process are discussed in detail.
Santhakumari, N C; Vallabhan, C P G(Elsevier, May , 1992)
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Abstract:
D.C. and a.c. electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium sulphate, (H3NCH2CH2NH3)(SO4), have been measured axiswise as a function of temperature. Anomalous variations in all the above properties at 480 K indicate the occurrence of a phase transition in the above material at this temperature. The existence of such a phase transition is also confirmed by DSC measurements. Electrical conductivity results are analysed and the activation energies of conduction at different temperature regions have been evaluated from the logσ vs 103T−1 plot. Possible mechanisms for the electrical conduction process are discussed, the available results being in favour of a proton transport model.
Santhakumari, N C; Vallabhan, C P G(Elsevier, April , 1991)
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Abstract:
dc and ac electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium dinitrate (EDN) have been measured axiswise as a function of temperature. All the above properties exhibit anomalous variations at 404 K thereby confirming the occurence of a phase transition in EDN at this temperature. Electrical conductivity parameters have been evaluated and possible conduction mechanisms are discussed. The role of protons in electrical trasport phenomenon is established by chemical analysis.
Syamaprasad, U; Dr.Girijavallabhan,C P(Cochin University of Science And Technology, December , 1981)
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Abstract:
The thesis aims to present the results of the
experimental investigations on the electrical properties like
electrical conductivity, dielectric constant and ionic thermo~
currents in certain ammonium containing ferroelectric crystals
viz. LiNH4SO4, (NH4)2SO4 and (NH4)5H(SO4)2. Special attention
has been paid in revealing the mechanisms of electrical conduction
in the various phases of these crystals and those asso~
ciated with the different phase transitions occurring in them,
by making studies on doped, quenched and deuterated crystals.
The report on the observation of two new phase transitions in
(NH4) S O2 and of a similar one in ( NH4 ) H (2SO4 ) are included. The relaxation mechanisms of the impurity-vacancy complexes and the space charge phenomena in pure and doped crystals of LiNH4SO4 and (NH4)2SO4 and the observation of a new type of ionic thermo-current viz. Protonic Thermo-Current (PTC) in these crystals are also presented here.
Description:
Department of Physics, Cochin University of Science and Technology
Abraham,P K; Dr.Sathianandan, K(Cochin University of Science and Technology, July , 1989)
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Abstract:
This thesis Entitled Electrical switching studies on the thin flims of polyfuran and polyacrylonitrile prepared by plasma polymerisation and vacuum evaporated amorphous silicon.A general introduction to the switching and allied phenomena is presented. Subsequently, developments of switching in thin films are described. The Mott transition is qualitatively presented. The working of a switching transitor is outlined and compared to the switching observed in thin films. Characteristic parameters of switching such as threshold voltage, time response to a, voltage pulse, and delay time are described. The various switching configurations commonly used are discussed. The mechanisms used to explain the switching behaviour like thermal, electrothermal and purely electronic are reviewed. Finally the scope, feasibility and the importance of polymer thin films in switching are highlighted.
Description:
Department of Physics, Division of Thin Film, Cochin University of Science and Tecnology
Dipyrromethene-Cu(II) derivatives possessing two dodecane alkyl chains have been used for the modification of gold
electrodes. Electroactive host molecules have been incorporated into a lipophilic dodecanethiol SAM deposited onto
gold electrodes through hydrophobic and van der Waals interactions (embedment technique). The presence of
dipyrromethene-Cu(II) redox centers on the electrode surface was proved by cyclic voltammetry and Osteryoung
square-wave voltammetry. The Au electrodes incorporating redox active Cu(II)-dipyrromethene SAMs were used for
the direct voltammetric determination of paracetamol in human plasma.
Girish Kumar,K; Joseph, Renjini(Taylor & Francis, June 1, 2009)
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Abstract:
A metalloporphyrin incorporated carbon paste sensor has been developed
for the determination of metronidazole benzoate (MTZB). Zn(II) complex
of 5,10,15,20-tetrakis (3-methoxy-4-hydroxy phenyl) porphyrin (TMHPP) was
used as the active material. The MTZB gave a well-defined reduction peak at
- 0.713V in 0.1 mol l -1 phosphate buffer solution of pH around 7. Compared
with bare carbon paste electrode (CPE), the TMHPP Zn(II) modified electrode
significantly enhanced the reduction peak current of MTZB as well as lowered
its reduction potential. Under optimum conditions the reduction peak current
was proportional to MTZB concentration over the range 1×10-3 mol1-1 to 1×10-5mol1-1. The detection limit was found to be 4.36×10-6mol1-1
. This
sensor has been successfully applied for the determination of MTZB in pharmaceutical
formulations and urine samples.
Girish Kumar,K; Thomas, D; Joseph, R; Issac, S; Lonappan, L(The Institution of Engineering and Technology, October 10, 2011)
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Abstract:
A differential pulse voltammetric sensor for the determination of tamsulosin hydrochloride (TAM) using multiwalled carbon nanotubes
(MWNTs)–Nafion-modified glassy carbon electrode (GCE) has been developed. MWNTs were dispersed in water with the help of Nafion
and were used to modify the surface of GCE via solvent evaporation. At MWNT-modified electrode, TAM gave a well-defined oxidation
peak at a potential of 1084 mV in 0.1 M acetate buffer solution of pH 5. Compared to the bare electrode, the peak current of TAM
showed a marked increase and the peak potential showed a negative deviation. The determination conditions, such as the amount of
MWNT–Nafion suspension, pH of the supporting electrolyte and scan rate, were optimised. Under optimum conditions, the oxidation
peak current was proportional to the concentration of TAM in the range 1 × 1023 M–3 × 1027 M with a detection limit of
9.8 × 1028 M. The developed sensor showed good stability, selectivity and was successfully used for the determination of TAM in pharmaceutical
formulations and urine samples
Harikumar,P S; Dr.Sivasankara Pillai, V N(Cochin University of Science and Technology, 1990)
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Abstract:
The primary aim of these investigations was to probe the elecnuchemical
and material science aspects of some selected metal phthalocyanines(MPcs).Metal phthalocyanines are characterised by a unique planar molecular structure. As a single
class of compounds they have been the subject of ever increasing number of physicochemical and
technological investigations. During the last two decades the literature on these compounds was
flooded by an outpour of original publications and patents. Almost every branch of materials science
has benefited by their application-swface coating, printing, electrophotography, photoelectrochemistry,
electronics and medicine to name a few.The present study was confined to the electrical and electrochemical properties of cobalt,
nickel, zinc. iron and copper phthalocyanines. The use of soluble Pes as corrosion inhibitor for
aluminium was also investigated.In the introductory section of the thesis, the work done so far on MPcs is reviewed. In this
review emphasis is given to their general methods of synthesis and the physicochemical properties.In phthalocyanine chemistry one of the formidable tasks is the isolation of singular species.
In the second chapter the methods of synthesis and purification are presented with necessary
experimental details.The studies on plasma modified films of CoPe, FePc, ZnPc. NiPc and CuPc are also presented.Modification of electron transfer process by such films for reversible redox systems
is taken as the criterion to establish enhanced electrocatalytic activity.Metal phthalocyanines are p- type semiconductors and the conductivity is enhanced by
doping with iodine. The effect of doping on the activation energy of the conduction process is
evaluated by measuring the temperature dependent variation of conductivity. Effect of thennal
treatment on iodine doped CoPc is investigated by DSC,magnetic susceptibility, IR, ESR and
electronic spectra. The elecnucatalytic activity of such doped materials was probed by cyclic
voltammetry.The electron transfer mediation characteristics of MPc films depend on the film thickness.
The influence of reducing the effective thickness of the MPc film by dispersing it into a conductive
polymeric matrix was investigated. Tetrasulphonated cobalt phthalocyanine (CoTSP) was
electrostatically immobilised into polyaniline and poly(o-toluidine) under varied conditions.The studies on corrosion inhibition of aluminium by CoTSP and CuTSP and By virtue of their anionic character they are soluble in water and are strongly adsorbed on aluminium.
Hence they can act as corrosion inhibitors. CoTSP is also known to catalyze the reduction of
dioxygen.This reaction can accelerate the anodic dissolution of metal as a complementary reaction.
The influence of these conflicting properties of CoTSP on the corrosion of aluminium was studied
and compared with those of CuTSP.In the course of these investigations a number of gadgets like cell for measuring the electrical
conductivity of solids under non-isothermal conditions, low power rf oscillator and a rotating disc
electrode were fabricated.
Description:
Department of Applied Chemistry,
Cochin University of Science and Technology
Sarin, V P; Nishamol, M S; Gijo,Augustin; Mohanan, P; Aanandan,C K; Vasudevan, K(John Wiley & Sons, July , 2008)
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Abstract:
A new design of a dual-band dual-polarized electromagnetically coupled slot loaded square patch antenna, covering the WLAN 5.2 GHz and 5.8 GHz bands, achieving bandwidth enhancement by using tapered slot structure, is presented here. The proposed antenna covers 5.09–5.47 GHz and 5.7–5.88 GHz bands. Details of the antenna design along with experimental and simulated results are presented and discussed.
In this paper, a dual port, dual frequency, dual polarized,
octagonal shaped Microstrip patch antenna, suitable for GPS
applications is discussed experimentally and theoretically. The
proposed antenna configuration is characterized by good
impedance bandwidth, gain, isolation between two ports and
broad radiation patterns
Description:
Personal Wireless Communications, 2005. ICPWC 2005. 2005 IEEE International Conference on,PP 305-307
Harilal, S S; Bindhu, C V; Issac, Riju C; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, September 1, 1997)
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Abstract:
Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained.
Geetha K, Varier; Harilal, S S; Bindhu, C V; Riju, C Issac; Nampoori, V P N; Vallabhan, C P G(December 3, 2011)
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Abstract:
Irradiation of a Polymethyl methacrylate target using a pulsed Nd-YAG laser causes plasma formation in the vicinity of the target. The refractive index gradient due to the presence of the plasma is probed using phase-shift detection technique. The phase-shift technique is a simple but sensitive technique for the determination of laser ablation threshold of solids. The number density of laser generated plasma above the ablation threshold from Polymethyl methacrylate is calculated as a function of laser fluence. The number density varies from 2×1016 cm-3 to 2×1017 cm-3 in the fluence interval 2.8-13 J · cm-2.
The electron-donor properties of Sm2O3 activated at 300, 500, and 800°C are reported from studies on the adsorption of electron acceptors of various electron affinities (electron affinity values in eV are given in parentheses): 7,7,8,8-tetracyanoquino-dimethane (2.84), 2,3,5,6-tetrachloro-1,4-benzoquinone (2.40), p-dinitrobenzene (1.77), and m-dinitrobenzene (1.26) in acetonitrile and 1,4-dioxane. The extent of electron transfer during the adsorption was determined from magnetic measurements. The acid-base properties of Sm2O3 at different activation temperatures are reported using a set of Hammett indicators. Electron donor-acceptor interactions at interfaces are important in elucidating the adhesion forces.
Sugunan, S; Jalaja, J M(Indian Journal of Chemistry, March , 1995)
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Abstract:
The electron donating properties of Ce02 and its mixed
oxides with alumina have been determined from the studies
of adsorption of electron acceptors of various electron
affinities on the surface of these oxides. The catalytic
activity of these oxides towards some reactions such as
oxidation of alcohols and reduction of ketones have been
Correlated with their surface electrondonor properties. The
surface acidity/basicity of these oxides have also been
determined by titration method using a set of Hammett
indicators.