• Volume 7, Issue 2

      July 1985,   pages  83-154

    • Growth of larger and more perfect single crystals of KClO4 in silica gel

      A Venkateswara Rao

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      As part of a continuing effort on crystal growth in gels, this paper describes the growth of large transparent single crystals of KClO4 by the improved design. The effect of various anionic and cationic components on nucleation, growth and quality of these crystals has been studied. It has been found that a combination of KNO3 and HClO4 as the reactants resulted in the best crystals in terms of crystal size, quality and inter-crystalline separation. The effect of various impurities on nucleation, growth and quality of these crystals has been studied. It has been found that the impurities which enhance the solubility of KClO4 have a positive effect on the size and quality of the crystals. A new etchant, consisting of concentrated HCl and H2SO4 in the volume ratio 2:3 has been found to reveal as-grown as well as freshly introduced dislocations.

    • Third order elastic constants of hexagonal boron nitride

      C S Menon

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      Third order elastic constants of hexagonal Boron Nitride have been evaluated using the Lannard-Jones potential. The results obtained are presented and compared with the only available measurement ofC333 for this material.

    • A minimal network model for creep

      M Krishnamoorthy V balakrishnan

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      We present a minimal rheological network model for the creep function in plastic flow. The model has a very small number of elements—a maximum of two linear springs, two Newtonian dashpots and a frictional mass. No non-Newtonian dashpots or other nonlinear elements are invoked. A wide variety of creep-curve shapes including those with inflection points across which the curvature changes sign are shown to be reproduced by the model and its sub-cases.

    • Studies on dynamicI-V curves of semiconductor-liquid junction cells formed with Cd0·8Zn0·2S films prepared at various spray rates

      M D Uplane S H Pawar

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      Cd0·8Zn0·2S films were prepared by the spray pyrolysis technique on glass and conducting glass (fluorine doped tin oxide) substrates, by spraying aqueous solutions of cadmium chloride, zinc chloride and thiourea. The spray rate was varied from 4 cc/min to 16 cc/min. It is found that film thickness increases with increase in spray rate. The electrical and optical properties of the films namely dark conductivity, thermoelectric power and optical absorption were studied; conductivity and thermoelectric power are higher for the films prepared at lower spray rate (4·3 cc/min).

    • Charge reversal in cadmium sulfide in diffusion controlled pattern formation process in agar gel

      N Palaniandavar N Kanniah F D Gnanam P Ramaswamy

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      Investigations were carried out to obtain the experimental conditions for the formation of a diffusion controlled revert pattern followed by a direct spatial pattern of bands in agar gel. The formation of revert to direct periodic pattern in the same tube is explained on the basis of adsorption, electrical double layer and charge reversal. On the basis ofdlvo and Shinohara’s theory, surface potential is calculated.

    • Variation of electrical properties in sepiolite during dehydration

      S Lokanatha S Bhattacherjee

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      The dielectric constant (K), loss (tanδ) andac conductivity of a sepiolite sample have been measured as a function of frequency in the range 102-107 Hz and in the temperature region 30–400°C. Thedc conductivities of hot pressed pellets were measured in the temperature range 30–550°C.K and tanδ of these samples decrease with increasing frequency. Results of these measurements have been correlated with the structural transformation accompanying dehydration, making use ofdta, ir and x-ray data. The moderately large value of activation energy (∼ 2·2 eV) in the intrinsic range suggests that the conduction process is most probably associated with ions.

    • Electrical conductivity of (PbO)1−x(SnO)x

      J C Garg N C Parakh

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      Electrical conductivity of lead tin monoxide has been measured as a function of composition (x), temperature and electric field. Heat treatment of samples in vacuum produces an irreversible increase in conductivity and is probably due to chemisorption of oxygen. The thermal activation energies in screen printed layers have been found to be lower than that in pressed pellets and is considered to be due to more grain boundaries being present in the former. The non ohmic electrical conduction in pellets followsJVn relationship wheren ranges between 2 and 1·25 for different compositions and temperatures. The theory of space charge limited currents (sclc) in defect insulators has been invoked to explain the observed results.

    • Thickness dependent properties of electro-chemical-photovoltaic (ecpv) cells formed with chemically deposited CdS films

      S H Pawar L P Deshmukh

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      Thin polycrystalline cadmium sulphide photoelectrodes of various thicknesses have been deposited on polished stainless steel substrates by a chemical bath deposition technique. The electrochemical photovoltaic (ecpv) cells were formed with these photoanodes. Short circuit current (Isc) and open circuit voltage (Voc) are recorded under 100 mW/cm2 light intensity. It is found thatIsc increases with increase in thickness of the photoanode whereasVoc remains more or less constant. The other cell parameters, maximum power output (Pm) and efficiency (η) are found to improve with increasing thickness, while fill factor (f.f.) varies slightly with the photoanode thickness. The semiconductor-liquid space charge region capacitances in the dark were measured. The variation of 1/C2 versus applied reverse biasV is nonlinear. The deviation from straight line behaviour is attributed to the existence of surface states and degeneracy of states. The flat band potential is determined from the extrapolation of the (1/C2) −V plot to the voltage axis, and is found to vary with the thickness of the photoanode.

    • Transparent conducting films

      T P Sharma C P Pandey

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      We present here a new technique, called vapour phase spray pyrolysis, for deposition ofto andito films. Undopedto film showed semiconducting nature, a sheet resistance of 1088 Ω/□, a donor ionization energy level of 40 meV, average visible transmittance of 75·4% andn-type conductivity. The indium doped (ito) film 10 wt % showed metallic nature, a sheet resistance of 15 Ω/□, average visible transmittance of 80·4 % andp-type conductivity. Thus theto andito films showed fairly good electro-optical qualities, comparable to those obtained by sophisticated and costly techniques.

    • Preparation and properties of iron-boron metallic glass ribbons melt spun in air

      D C Agrawal E A Chakachery

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      The preparation of metallic glass ribbons by melt spinning is a simple technique; however, a researcher often faces many problems when undertaking the preparation of such ribbons. The difficulties encountered are oxidation of the melt, choking of the nozzle by the solidified metal, formation of metal globules or ribbon fragments, oxidation of the ribbons, etc. These problems are particularly severe when working with high melting point alloys. This report describes certain experimental techniques used to overcome problems in preparation of metallic glass ribbons of iron-boron and other high melting point alloys. The ribbons thus produced have been characterized by transmission electron microscopy, mechanical tests and differential thermal analysis. The mechanical strength of the ribbon is comparable to the best recorded strength for ribbons of similar composition. Thedta data support the view that the formation of the phase Fe23B6 takes place upon crystallization of the eutectic alloy.

    • Auger recombination rate in quantum well lasers

      P K Basu

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      Auger recombination is the dominant non-radiative process in InGaAsP quantum well lasers and is responsible for the poor temperature dependence of the threshold current density. In all recent calculations of the Auger rate the electron-electron interaction potential is taken to be either of the bulk form or an approximate form derived from it. In the present work, the rate is calculated by taking an appropriate potential valid for quasi two-dimensional electrons and the expected changes are pointed out. The calculated Auger life-time is in agreement with the values reported in the literature.

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