• Volume 20, Issue 7

      October 1997,   pages  909-1028

    • Studies of structural and electrical properties of Pb(Li1/4Eu1/4Mo1/2)O3 ceramics

      S Bera R N P Choudhary

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      Polycrystalline sample of Pb(Li1/4Eu1/4Mo1/2)O3 was prepared by usual ceramic route. X-ray diffraction, SEM and EDAX were used to check the formation, homogeneity and elements present in the compound. The measurement of dielectric constant (ɛ), dielectric loss (tanδ), hysteresis loop parameters (e.g. spontaneous polarization) as function of frequency and temperature suggest that the compound is a ferroelectric one and has a ferro-paraelectric phase transition at 112 ± 2°C. The measurement of dc resistivity both as function of biasing electric field and temperature of the compound suggests that the compound has negative temperature coefficient (NTC) of resistance above 100°C.

    • Effect of magnetic field, thermal cycling and bending strain on critical current density of multifilamentary Bi-2223/Ag tape and fabrication of a pancake coil

      T K Dey M K Chattopadhyay

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      Multifilamentary HTSC tapes are important for their applications in various electrical devices. Powder-in-tube technique with improved optimized synthesis parameters is regarded as one of the most promising ways to prepare long-length multifilamentary Bi-2223/Ag tapes. Nevertheless, usefulness of such tapes depends on their electrical and mechanical properties. Critical current density of a Bi-2223/Ag tape with 37 filaments has been studied at 77 K with field, field orientation, thermal cycling and bending strain as parameters. Results have been discussed in light of various mechanisms and models. A small pancake coil has been fabricated out of the same tape and the test results presented.

    • Evidence of two ferroelectric PTCR components in valence-compensated ceramic system Ba1−xLaxTi1−xCoxO3

      Lakshman Pandey Rajesh K Katare Om Parkash Devendra Kumar

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      The electrical behaviour of valence-compensated ceramic system Ba1−xLaxTi1−xCoxO3 has been studied as a function of temperature (300–600 K) and composition (x ⩽ 0·20), using the method of impedance spectroscopy. The necessary equivalent circuit models that represent the data best have been obtained using impedance and modulus formalisms and grain and grain boundary contributions have been separated out. The compositionsx = 0·20 and 0·10 show a negative temperature coefficient of resistance (NTCR) behaviour whereas a very small variation of the grain and grain boundary resistance with temperature is observed forx = 0·05. A positive temperature coefficient of resistance (PTCR) behaviour having two ferroelectric components is observed forx = 0·01. These results reveal limitations in current theories of the PTCR effect.

    • Constitution and properties of ceramized fireclay refractories: I. Constitution

      S P Chaudhuri B K Bhaumik

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      A poor-grade fireclay was mixed with three nucleating agents, namely Cr2O3, V2O5 and TiO2. The fireclay and oxide mixed fireclay were fired at 1300°C for 1 h, cooled down to room temperature and then heat-treated at 1150°C for 15h. These were also heat-treated at 1150°C for 15 h after cooling down to 1150°C from the peak temperature. The heat-treatment caused ceramization of the glassy phase in the fireclay samples, and the samples, mineralogical composition and microstructure were investigated. Ceramization brought about significant changes in the microstructure only.

    • Constitution and properties of ceramized fireclay refractories: II. Properties

      S P Chaudhuri B K Bhaumik

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      Low-grade fireclay refractories contain large amounts of glassy phase. The properties, e.g. mechanical strength, thermal-shock resistance, refractoriness-under-load, refractoriness and also porosity and bulk density of these refractories before and after ceramization of their glassy phase were investigated. The glassy phase was ceramized by incorporating Cr2O3, V2O5 and TiO2 into the refractories as nucleating agents and subsequent heat-treatment. Significant improvement in mechanical strength and thermal-shock resistance of the ceramized refractories was observed.

    • A new inexpensive method for the preparation of acicular precursors for magnetic recording media

      M R Anantharaman K V Joseph H V Keer

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      Magnetic materials meant for audio/video recording applications necessitate that polycrystalline materials be in acicular shape. So preparation of acicular precursors for magnetic storage materials assumes significance. The employment of aqueous solutions do not produce needle shape crystallites. Glycerol is one of the complexing media used for the precipitation of ferrous oxalate dihydrate. An inexpensive method using starch for preparation of acicular particles is described. The influence of an additive namely Gd on acicularity is also investigated.

    • Ultrasonic properties of composites (polymer-fibre glass)

      N A Abd El-Malak

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      Majority of composite materials used in industry consist of polyester as a matrix and fibre glass as a reinforcement material. Five samples with different fibre glass contents were studied ultrasonically, using pulse echo technique to determine their ultrasonic properties. Results showed that the ultrasonic velocity, elastic moduli and activation energies associated with their relaxation process increase with the increase of the fibre glass content. The study showed the utility of using these inexpensive materials as sound absorbing devices and as backing materials in the manufacture of ultrasonic transducers.

    • Influence of steam sterilization induced surface changes of polyester materials on its biocompatibility

      P D Nair P J Doherty D F Williams

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      Steam sterilization is conventionally used for the sterilization of materials used in surgery and medicine. When subjected to repeated steam sterilization, oligomers of polyethylene terephthalate are produced on the surface of the polyester materials. The consequences of the production of such oligomers on the biocompatibility of the polyester material have been investigated. Growth inhibition of L929 fibroblast cells has been observed on the repeatedly sterilized materials in thein vitro cell-material contact studies.In vivo implantation of the repeatedly sterilized materials elicited a hostile tissue response comprising enhanced macrophage activity, which could have an adverse effect on the long term stability of the polyester materials.

    • Thermally-stimulated spontaneous currents from metal-iodine doped polyvinyl pyrrolidone-metal system

      P K Khare Sandeep K Jain Sunil K Paliwal

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      A study of the spontaneous response currents from the metal-iodine doped polyvinyl pyrrolidone-metal (MPM) systems, on thermal stimulation at a constant rate, has been made with similar (Al-Al, Ag-Ag and Au-Au) and dissimilar (Al-Cu/Ag/Ni/PbZn) electrode systems. Thermograms of spontaneous current emission of iodine-doped PVP films exhibit two maxima around 90 ± 10°C and 130–160°C in the first heating run, whereas with the second heating run a single peak is found around 140–170°C. The magnitude and direction of current depend on the choice and combination of electrode materials. The position of the current peak in the thermal spectrum shifts with different heating run. A temperature dependence of open-circuit voltage (OCV) is also reported and it was found that OCV varied linearly with the difference in electrode work functions. The active centres of PVP are the carbonyl group of double-bond tertiary nitrogen atom (> N-C=O), and thus the charge transfer complexes are formed with iodine in PVP. The spontaneously-generated current is discussed in terms of weak complex formation with the water molecules and the liberation of different types of charges.

    • n-CuInS2/polysulfide photoelectrochemical solar cells prepared by spray pyrolysis

      Y D Tembhurkar

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      n-CuInS2 photoanode has been prepared by spray pyrolysis onto SnO2 deposited glass substrate at 350°C. The conductivity type of the photoanode was tested by hot-probe method and was ofn type. The conductivity of the photoanode was of the order of 2–4Θ−1cm−1 and was measured by using four-probe method. The effect of etching (HCl:HNO3 = 5:1 by volume) on photoanode properties has been studied. The best cell had the following parameters:Voc = 0·29V,Isc = 5·33 mA/cm2,ff = 0·571 and η = 1·275%.

    • Composition dependence of electrical properties of Al-Sb thin films

      P S Nikam R Y Borse R R Pawar

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      Thin films of Al-Sb of varying compositions and thickness have been formed on glass substrates employing three-temperature method. Electrical resistivity (ρ) and activation energy (ΔE) have been studied as a function of composition, thickness (d) and temperature of the film. Films of Al-Sb system with aluminium < 50 at.%, ∼ 50 at.% and > 50 at.% exhibit metallic, semiconducting and metallic to semiconducting behaviours respectively. Activation energy (ΔE) of semiconducting films found to vary inversely with thickness, is attributed to combined effects of change in barrier height due to the size of grains and stoichiometry in the films.

    • Thermal expansion studies on ferroelectric materials

      M V Radhika Rao A M Umarji

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      Thermal expansion data is reported over a wide temperature range (80–800 K) for BaTiO3 (BT) and Pb(Fe1/2 Nb1/2)O3 (PFN), belonging to different classes of the ferroelectric materials. The sharp structural phase transitions of BT result in lowering of the thermal expansion coefficient (α) at the transitions which is proportional to the change in polarization at the transitions. In PFN, a relaxor ferroelectric, lowering of α is spread over a wider temperature range across the dielectric maxima.

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