• Issue front cover thumbnail

      Volume 28, Issue 1

      February 2005,   pages  1-79

    • Hydrothermal synthesis, structure and characterization of new NASICON related potassium iron (III) pyrophosphate

      G S Gopalakrishna B H Doreswamy M J Mahesh M Mahendra M A Sridhar J Shashidhara Prasad K G Ashamanjari

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      A new potassium iron (III) pyrophosphate was synthesized by hydrothermal technique and characterized by X-ray studies. The compound crystallizes in a monoclinic space group, 𝑃21/𝑐, with cell parameters, 𝑎 = 7.365(2) Å, 𝑏 = 10.017(2) Å, 𝑐 = 8.214(1) Å, 𝛽 = 106.50(1)° and 𝑍 = 4. The structure has tunnel-type cavities and are congenial for ion transportation through them. The compound exhibits moderate thermal stability.

    • Indium oxide thin film based ammonia gas and ethanol vapour sensor

      K K Makhija Arabinda Ray R M Patel U B Trivedi H N Kapse

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      A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature.

      The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.

    • A strategic approach for preparation of oxide nanomaterials

      K J Rao Krishnamurthy Mahesh Sundeep Kumar

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      A microwave assisted solvothermal method is described for rapid preparation of nano-oxides. This method is based on exploiting differential dielectric constants to induce preferred heating and decomposition of the oxide precursors in the presence of suitable capping agents. This strategic approach has been used to prepare nanopowders of MgO, NiO, ZnO, Al2O3, Fe2O3 and ZrO2.

    • A new crystal structure for (BEDT–TTF)2SbF6 and some of its physical properties

      G K R Senadeera T Mori

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      A new crystal structure for bis(ethylenedithio)tetrathiafulvalene [(BEDT–TTF)2 SbF6] was determined by single crystal X-ray diffraction. The crystal structure was refined in the $P \overline{1}$ space group at room temperature. Crystal data for new structure are as follows: triclinic, 𝑎 = 8.670 (2) Å, 𝑏 = 8.664 (2) Å, 𝑐 = 16.842 (5) Å, 𝛼 = 89$^\circ \cdot$29 (2), 𝛽 = 90$^\circ \cdot$71 (3), 𝛾 = 92$^\circ \cdot$67 (1), 𝑉 = 1263.64 Å3, 𝑍 = 2, 𝐷𝑥 = 2.136 g cm-3, (Mo–K𝛼), 𝛾 = 0.7107 Å, 𝑅 = 0.057 for a total of 5517 independent reflections. The donors form a trimerized column, and the band structure calculated by the tight-binding approximation shows band insulator properties. The temperature dependent of the d.c. resistivity shows a semiconducting behaviour with room temperature resistivity along the 𝑐-axis; $\rho_{290 K}$ = 5.6 ohm cm.

    • Luminescent studies of impurity doped SrS phosphors

      Vijay Singh Manoj Tiwari T K Gundu Rao S J Dhoble

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      SrS phosphors activated with Ce and Dy ions were prepared by solid-state diffusion method. Photoluminescent study was carried out on SrS : Ce, SrS : Dy and SrS : Dy, Ce. Thermoluminescence and electron spin resonance studies were also carried out on SrS : Dy phosphor. The thermoluminescence glow curve shows a peak at around 142°C. Irradiated SrS : Dy exhibits an ESR line due to a defect centre. Thermal annealing behaviour indicates that this centre correlates with the TL peak at 142°C. The centre is characterized by an isotropic g-value of 2.0039 and is assigned to a 𝐹+ centre.

    • X-ray and magnetic studies of Zn2+ substituted Ni–Pb ferrites

      M C Sable B K Labde N R Shamkuwar

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      Seven samples of the polycrystalline, Ni1.25–𝑥Zn𝑥Pb0.25Fe1.5O4 (𝑥 = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ferrites, were prepared by usual double sintering ceramic method. X-ray diffraction patterns of the samples revealed single-phase cubic spinel structure. The magnetic properties were investigated by means of magnetization and a.c. susceptibility (𝜒) measurements. A.C. susceptibility was measured from room temperature to the Curie temperature (𝑇C) of the samples. Variation of a.c. susceptibility (𝜒) with temperature showed that the samples with 𝑥 = 0.3 and 0.5 contain single-domain (SD) particles whereas the samples with 𝑥 = 0.4 and 0.6 showed multi-domain (MD) nature. Values of Curie temperature (𝑇C) as obtained from the study of variation of a.c. susceptibility with temperature were found to decrease with increase in the Zn2+ concentration (𝑥). Magnetic measurements showed increase in magnetization as Zn2+ content was increased from 0.0 to 0.5. Further increase in Zn2+ content (𝑥) reduces the magnetization.

    • Ba2ErNbO6: A new perovskite ceramic substrate for Bi(2223) superconducting thick films (𝑇c(0) = 110 K)

      S U K Nair P R S Warriar J Koshy

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      Barium erbium niobate (Ba2ErNbO6) has been developed as a new substrate for (Bi,Pb)2Sr2Ca2Cu3O𝑥 [Bi(2223)] superconductor film. Ba2ErNbO6 (BENO) has a cubic perovskite structure with lattice constant, 𝑎 = 8.318 Å. The Bi(2223) superconductor does not show any detectable chemical reaction with BENO even under extreme processing conditions. Dip coated Bi (2223) thick film, Ba2ErNbO6 substrate, gave a 𝑇c (0) of 110 K and current density of ∼ 4 × 103 A cm-2 at 77 K and zero magnetic field.

    • Preparation and study of thickness dependent electrical characteristics of zinc sulfide thin films

      A U Ubale D K Kulkarni

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      Zinc sulfide thin films have been deposited onto glass substrates by chemical bath deposition. The various deposition parameters such as volume of sulfide ion source, pH of bath, deposition time, temperature etc are optimized. Thin films of ZnS with different thicknesses of 76–332 nm were prepared by changing the deposition time from 6–20 h at 30°C temperature. The effect of film thickness on structural and electrical properties was studied. The electrical resistivity was decreased from 1.83 × 105 𝛺-cm to 0.363 × 105 𝛺-cm as film thickness decreased from 332 nm to 76 nm. The structural and activation energy studies support this decrease in the resistivity due to improvement in crystallinity of the films which would increase the charge carrier mobility and decrease in defect levels with increase in the thickness.

    • Oriented growth of thin films of samarium oxide by MOCVD

      K Shalini S A Shivashankar

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      Thin films of Sm2O3 have been grown on Si(100) and fused quartz by low-pressure chemical vapour deposition using an adducted 𝛽-diketonate precursor. The films on quartz are cubic, with no preferred orientation at lower growth temperatures (∼ 550°C), while they grow with a strong (111) orientation as the temperature is raised (to 625°C). On Si(100), highly oriented films of cubic Sm2O3 at 625°C, and a mixture of monoclinic and cubic polymorphs of Sm2O3 at higher temperatures, are formed. Films grown on either substrate are very smooth and fine-grained. Infrared spectroscopic study reveals that films grown above 600°C are free of carbon.

    • Influence of 𝛽-cyclodextrin as an encapsule and as an inclusion complex dopant on conducting polyaniline

      E Subramanian G Anitha M Karthik Selvam M Ibrahim Ali Badusha

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      An investigation on the effect of 𝛽-cyclodextrin (CD) in both free and inclusion-complexed forms with a guest anionic metal complex, dioxalatodiaquochromate(III) (DDC), on the characteristics of conducting 2–polyaniline (PANI) is carried out. Four materials, PANI (i.e. PANI–SO4), PANI–DDC, PANI–CD and PANI–CD + DDC were prepared by in situ chemical oxidative polymerization in aqueous H2SO4 at pH 1 and subjected to electrical conductivity and spectral (IR and UV-vis) measurements. DDC and CD when separately incorporated, reduce the conductivity of PANI by about half whilst their inclusion complex CD + DDC enhances it. Spectral characterization reveals that DDC as a dopant and CD as an encapsule exhibit their effects through adverse interaction with imine–amine N centres and benzenoid moiety of PANI. The inclusion complex CD + DDC, on the contrary, functions as a dopant by lying in between the chains and seems to promote the extended conformation of PANI chain and hence the 𝜋-electron delocalization. Exposure of the material to methanol vapour causes a decrease in conductivity in PANI and PANI–CD while an increase in PANI–CD + DDC. This study makes explicit the distinct role of CD as an encapsule and CD + DDC inclusion complex as a dopant in altering the electrical property of PANI.

    • Effect of Cr and Ni on diffusion bonding of Fe3Al with steel

      Wang Juan Li Yajiang Ma Haijun

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      Microstructure at the diffusion bonding interface between Fe3Al and steel including Q235 low carbon steel and Cr18–Ni8 stainless steel was analysed and compared by means of scanning electron microscopy and transmission electron microscopy. The effect of Cr and Ni on microstructure at the Fe3Al/steel diffusion bonding interface was discussed. The experimental results indicate that it is favourable for the diffusion of Cr and Ni at the interface to accelerate combination of Fe3Al and steel during bonding. Therefore, the width of Fe3Al/Cr18–Ni8 interface transition zone is more than that of Fe3Al/Q235. And Fe3Al dislocation couples with different distances, even dislocation net occurs at the Fe3Al/Cr18–Ni8 interface because of the dispersive distribution of Cr and Ni in Fe3Al phase.

    • Diffusivity of Al and Fe near the diffusion bonding interface of Fe3Al with low carbon steel

      Li Yajiang Wang Juan Yin Yansheng Ma Haijun

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      The distribution of elements near the Fe3Al/Q235 diffusion bonding interface was computed by the diffusion equation as well as measured by means of EPMA. The results indicated close agreement between the two for iron and aluminium. Diffusion coefficient in the interface transition zone is larger than that in the Fe3Al and Q235 steel at the same temperature, which is favourable to elemental diffusion. The diffusion distance near the Fe3Al/Q235 interface increased with increasing heating temperature, 𝑇, and the holding time, 𝑡. The relation between the width of the interface transition zone, 𝑥, and the holding time, 𝑡, conformed to parabolic growth law: 𝑥2 = 4.8 × 104 exp(– 133/RT) (𝑡 – 𝑡0). The width of the interface transition zone does not increase significantly for holding times beyond 60 min.

    • Influence of ageing, inclusions and voids on ductile fracture mechanism in commercial Al-alloys

      A Chennakesava Reddy S Sundar Rajan

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      The objective of the paper is to study the effect of ageing, inclusions and voids on the mechanism of fracture and resultant toughness. It has been found that the voids are initiated at only a fraction of the larger inclusions present. The initiation of voids at small particles in the ductile fracture process appears to have little effect on fracture toughness. The strain hardening capacity has a marked effect on void size, and is an indicator of fracture toughness in the commercial Al alloy.

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