• Volume 3, Issue 3

      November 1981,   pages  245-389

    • Preface

      C N R Rao J M Honig

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    • Skull melting as a technique in the growth of single crystals

      H R Harrison J M Honig

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      The growth of single crystals of many oxides is very difficult because of their high melting points, and in some cases, because of their extreme corrosiveness. Skull melting makes possible the preparation of many oxides because it is a crucibleless process, there is no theoretical limit as to the temperature that can be attained, and there is no intrinsic limitation on the oxygen pressure that may be used. A detailed description of how to set up a skull melting system and a detailed operating procedure are provided.

    • Low-temperature preparation of some perovskites La2MM′O6 (M, M′=Cr, Mn, Fe, Co, Ni, M≠M)

      P Ganguly

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      The low-temperature preparation of some La2MM′O6 compounds (M,M′=Cr, Mn, Fe, Co, Ni, M≠M′) by the decomposition of coprecipitated basic carbonates is described. Single phase compounds are formed. The stability of physical properties of these phases towards further heating depends on the M and M′ ions. The results are interpreted in terms of the stability of the M-M′ oxidation states.

    • Stabilization of unstable oxides

      C E Deshpande M N Sankarshana Murthy

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      Easily oxidizable oxides, FeO, and MnO, are unstable in air but can be easily stabilized by small amounts of other oxides. Further these two unstable oxides stabilize each other very well. Such stabilized FeO and MnO provide easy and reproducible methods of preparing electronic ceramics that need such unstable valency states in them. Ferrous-zinc ferrite has been successfully synthesized employing FeO stabilized with a small amount of Fe3O2.

    • Preparation of some transition metal sulphides

      J Gopalakrishnan

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      Ternary sulphides, LnMS3 (Ln=rare earth metal; M=first row transition metal) and MV2S4 (M=Mg, Fe, Co, Ni and Zn) have been prepared by the reaction of appropriate ternary metal oxides with H2S or CS2/N2 vapours at elevated temperatures. Chemical analysis and x-ray powder diffraction of the products indicate formation of single-phases with unique crystal structures in many cases.

    • Synthesis and characterization of γ-Fe2O3 — a magnetic tape material

      M R Anantharaman K Seshan D K Chakrabarty H V Keer

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      Acicular FeC2O4 · 2H2O was precipitated from glycerol and starch media. Thermal decomposition of this oxalate in dry and moist nitrogen yielded primarily FeO and Fe3O4 respectively. Characterization was attempted through DTA, TG, x-ray diffraction, TEM and magnetization studies. It was found that the oxalate can be completely decomposed to Fe3O4 in moist nitrogen (PH2O ∼ 35 torr) at 775 K and then oxidised by dry air to acicular γ-Fe2O3 at 575 K. The resulting material has saturation magnetization (∼ 70 emu/g), coercive field (∼ 300 Oe) and squareness ratio (∼ 0·60–0·65), which values art comparable with those of the commercial samples.

    • Preparation and characterization of some single, mixed and doped crystals and instrumentation aspects

      R Krishnaswamy

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      The preparation and characterization (salient ones) of KAl (SO4)2. 12H2O, KCr (SO4)2·12H2O, mixed crystals of both with 10 to 90% of each component, mixed crystals of CsCl with CuCl2, doped crystals of KBr with K3FeCN6, mixed crystals (NH4)2SO4 with CuSO4 or NiSO4, NaCl with growth improver Pb+2, Mn+2, metallic crystals of Zn, Bi, ionic crystals of alkali halides with Pb+2, or Cd+2, etc. are presented. Instrumentation aspects of a rotary crystallizer, a homogeniser, an ingot release mechanism and a zone refiner are shown.

    • Preparation and sensitization of tin telluride infrared detectors

      S Santhanam A K Chaudhuri

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      The compound tin telluride was prepared with the constituent elements (Sn and Te) by using the standard fusing technique. From x-ray studies the compound was identified as tin telluride. The detectors in the form of thin films were prepared by vacuum evaporation. Conductivity and photoconductivity measurements of the detectors were carried out in the temperature range of 130 to 300 K. These detectors were sensitized by baking them in air at a fixed temperature (413 K) for a fixed time (1800 sec). Resistivity measurements of the detectors with consecutive bakings were also carried out. The photosensitivity of the detectors increases as it is baked reaching an optimum value after which the sensitivity decreases whereas the resistivity of the detectors increases continuously with baking. It is observed that photosensitivity of the detectors increases with decrease of temperature. The increase of sensitivity with baking has been explained on the basis of modulation of barrier due to the development of photovoltage at SnTe and its oxide heterojunctions.

    • Preparation and characterization of Pb1−xSnxTe pseudobinary alloy semiconductors

      S C Das A K Chaudhuri S Bhattacharya

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      Ap-type pseudo-binary alloy semiconductor, Pb0·3Sn0·7Te, has been prepared fromp-type specimens of PbTe and SnTe and lattice constants determined with an accuracy of 0.0001 nm. Vacuum annealing of Pb0·3Sn0·7 Te reveals two new x-ray powder diffraction lines bearing indices (444) and (800), while others become more sharp, CuKa-doublets get clearly resolved and the lattice constant is increased by ∼ 0·0002 nm. Slight deviation from Vegard’s law linearity is observed showing that the sample must be considered as ternary in nature. Thin films deposited on mica and glass substrates kept at room temperature are found to have a little higher SnTe content. The effective carrier concentration calculated from Hall measurements at room temperature is ∼ 3·4×1026 m−3.

    • Growth and electro-optic studies in mixed (NH4)x K1−xH2PO4 single crystals

      K B R Varma Kolluri V Ramanaiah

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      Single crystals and mixed crystals of KH2PO4 (KDP) and NH4H2PO4 (ADP) were grown with different dopant concentrations of NH4H2PO4 in KH2PO4 in solution by Holden’s rotary crystallizer technique. The effect of additives like Borax (Na2B4O7·10H2O), seed crystal rotation rate and qualities of the crystals were studied. The half-wave voltages (in longitudinal mode) for KDP mixed with 1% ADP (by weight) were found and hence the unclamped (low frequency) electro-optic coefficients (r63) were calculated for various wavelengths in the visible region of the spectrum. It was noted that the half-wave voltage increases with increase in wavelength and temperature.

    • Preparation and structural characterisation of chemically deposited Pb1−xCdxS films

      B B Nayak H N Acharya G B Mitra

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      Alloy films of Pb1−xCdxS have been prepared on glass substrates by electroless deposition from a chemical bath. Structural characterisation of the alloy was carried out by x-ray powder diffraction technique using Debye-Scherrer camera. The study shows that Pb1−xCdxS exists in cubic phase and the lattice constants are found to be greater than individual CdS and PbS value. This expansion of lattice is possibly due to interstitials. The lattice constants have been found to vary linearly with atomic percent of cadmium sulphide. The SEM micrographs show that particle size increases with increase in atomic percent of cadmium sulphide in the alloy.

    • Electron transport in hot pressed Y3−xGdxFe5O12

      D Bahadur OM Parkash Devendra Kumar

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      Electron transport properties of a few hot-pressed garnets of the series Y3−xGdxFe5O12 (wherex=0, 1 and 2·4) have been measured. For comparison, a normal sintered YIG has been studied to see the effect of porosity and microstructure. The electron transport properties have been discussed on the basis of the model suggested by Austin and Mott keeping in view the distortion caused by the substitution.

    • Moisture absorption and its effect on the electrical properties of high silica fabric

      B E Rama Chandran N Balasubramanian G V Subba Rao G Aravamudan

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      High silica fabric with a silica content >98% can be prepared by removing the non-siliceous ions from the E-glass fabric using HCl as the leachant. The presence of Si-OH groups makes the material hydrophilic. The extent of moisture absorption depends on the extent of leaching. The moisture present in the leached fabric decreases the volume and surface resistivity values.

    • Phase transitions in molybdenum sesquisulphide systems between 80 and 600 K

      A K Rastogi R K Ray

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      Samples of Mo2S3 system and substituted derivatives with Cr, Nb, Cu and Mn have been studied. The resistivity, thermoelectric power, magnetic susceptibility and specific heat indicate clear phase transition at temperatures between 200 and 310 K. X-ray investigations establish the transitions at these temperatures as structural changes. Careful analysis of the data helps to obtain working values for a model for the energy band. Carrier density, effective mass, mobility, band overlap parameter, density of states for the electrons and holes in the overlapping bands at the Fermi level and the band gap for a higher conduction band are obtained.

    • Characterization of a-Si:H thin films prepared by dc glow discharge of silane

      D S Misra P N Dixit S C Agarwal

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      A dc glow discharge apparatus for preparing amorphous silicon films from silane gas is described. The films are characterized by electron microscopy, infrared spectroscopy, electrical conductivity and photoconductivity. The deposition parameters which give good photoconducting films are established. The Staebler-Wronski effect is studied and is found to be smaller in vacuum than in air. A photovoltage is observed in structures with gold as the Schottkybarrier metal. The conversion efficiency of the device is about 1%. The results are compared with those in the literature, and the improvements which might result in a better conversion efficiency are pointed out.

    • Inorganic materials for optical data storage

      SK Date

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      Recyclable holographic (optical) storage in inorganic materials is nowadays possible due to the advent of laser. Various performance parameters of the state-of-the-art of optical storage are discussed in detail with reference to the well-established case of ferroelectric lithium niobate (LiNbO3). Various physicochemical techniques are employed in understanding the microscopic mechanisms responsible for optical storage in LiNbO3. A short summary of other inorganic materials capable of holographic storage is also presented.

    • Characterisation of high purity rare-earth oxides by x-ray fluorescence methods

      R M Dixit

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      X-ray fluorescence methods for the determination of individual rare earth impurities in high purity rare earth oxidesviz., Y2O3, La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3 and Er2O3 have been developed in our laboratory. The samples are converted to oxalate form and double-layer pellets are prepared using boric acid as binding material. A semiautomatic x-ray spectrometer is used for the analyses. Choice of instrumental parameters and analysis lines is discussed. The determination range varies from 0.005% to 1.0% for most elements with good precision and adequate accuracy.

    • Elemental characterisation of aluminium used in reactors by optical emission spectroscopic methods

      L C Chandola

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      Using AC spark, AC arc and DC arc excitations in optical emission spectroscopic systems, the Al metal used in reactors can be characterised for its minor or trace element composition. The best precision of ± 6% is obtained with an AC spark in which the rod sample is taken as a self electrode and elements Cu, Fe, Mn, Si and Ti are determined in the concentration range 0·01–1%. The oxide powder sample with DC arc excitation provides best minimum detection limits of 10 ppm in general and 21 trace elements are determined by it. The AC arc method also uses oxide powder standards prepared synthetically and determines B and Mg in addition to the elements determined in AC spark excitation with a precision of ±9%.

    • Scanning electron microscopic fractography of permanent moulded cast iron

      S Seetharamu Malur N Srinivasan

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      The fracture susceptibility of chill-free permanent moulded cast iron is discussed in terms of graphite configuration. The details of fracture surface topography as revealed by scanning electron microscope examination on areas of slow crack growth and fast fracture are presented and the usefulness of these SEM fractographs in categorizing the fracture modes is demonstrated.

    • Announcement

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