• Issue front cover thumbnail

      Volume 35, Issue 1

      February 2012,   pages  1-127

    • Structural and optical characterization of thick and thin polycrystalline diamond films deposited by microwave plasma activated CVD

      S K Pradhan B Satpati B P Bag T Sharda

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      Preliminary results of growth of thin diamond film in a recently installed 3 kW capacity microwave plasma activated CVD (MW-PACVD) system are being reported. The films were deposited on Si (100) substrate at 850°C using methane and hydrogen mixture at 1.5 kW MW power. The grown polycrystalline films were characterized by micro-Raman, transmission electron microscope (TEM), spectrophotometer and atomic force microscope (AFM). The results were compared with that of a thicker diamond film grown elsewhere in a same make MWPACVD system at relatively higher power densities. The presence of a sharp Raman peak at 1332 cm-1 confirmed the growth of diamond, and transmission spectra showed typical diamond film characteristics in both the samples. Typical twin bands and also a quintuplet twinned crystal were observed in TEM, further it was found that the twinned region in thin sample composed of very fine platelet like structure.

    • Recent analytical applications of nanoparticle sensitized lucigenin and luminol chemiluminescent reactions

      S M Wabaidur Mu Naushad Z A Alothman

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      There is an ever-increasing demand for rapid, sensitive, cost effective and selective detection methods for the analysis of many essential compounds.When chemiluminescence has been introduced to analytical chemistry as a detection technique, it has been shown to meet many of these requirements. This method has become a powerful tool for the determination of many compounds. Using this method, low detection limits can be obtained with simple and inexpensive instrumentation. Coupled with flow injection technique the method has become more popular for wider applications. Since many excellent reviews on the chemiluminogenic techniques have appeared in the literature in recent years, the present paper does not intend to cover the exhaustive studies in this area, but will selectively describe the analytical applications of nanoparticle sensitized lucigenin and luminol chemiluminescent reactions and evaluate their recent progress together with our present work.

    • Effects of nitrogen annealing on surface structure, silicide formation and magnetic properties of ultrathin films of Co on Si(100)

      Ganesh K Rajan Shivaraman Ramaswamy C Gopalakrishnan D John Thiruvadigal

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      Effects of nitrogen annealing on structural and magnetic properties of Co/Si (100) up to 700°C has been studied in this paper. Ultrathin Co films having a constant thickness of 50 Å were grown on Si (100) substrates using electron-beam evaporation under very high vacuum conditions at room temperature. Subsequently, the samples were annealed at temperatures ranging from 100–700°C in a nitrogen environment at atmospheric pressure. Sample quality and surface morphology were examined using atomic force microscopy. Silicide formation and the resultant variation in crystallographic arrangement were studied using X-ray diffractometer. The magnetization measurements done using a vibrating sample magnetometer indicate a decrease in coercivity and retentivity values with increase in annealing temperature. Resistivity of the samples measured using a four-point probe set up shows a decrease in resistivity with increase in annealing temperature. Formation of various silicide phases at different annealing temperatures and the resultant variation in the magnetic susceptibility has been thoroughly studied and quantified in this work.

    • Dielectric properties and structural dynamics of melt compounded hot-pressed poly(ethylene oxide)–organophilic montmorillonite clay nanocomposite films

      R J Sengwa Shobhna Choudhary

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      The dielectric properties of melt compounded hot-pressed nanocomposite films consisting of a poly(ethylene oxide) (PEO) and organophilic montmorillonite (OMMT) clay surface modified with trimethyl stearyl ammonium as filler with increasing amount up to 20 wt.% OMMT were investigated in a frequency range of 20 Hz–1 MHz at 30 °C. The predominance of OMMT exfoliated structures in PEO–OMMT nanocomposites were recognized by a decrease of the real part of complex dielectric function. OMMT concentration dependent dielectric and electric modulus relaxation times have revealed that the interactions compatibility between PEO molecules and dispersed OMMT nano-platelets in PEO matrix governs the PEO segmental dynamics. A.C. conductivity of these nanocomposites increases by two orders of magnitude in the experimental frequency range.

    • Ultrasound assisted synthesis of PMMA/clay nanocomposites: Study of oxygen permeation and flame retardant properties

      Subrata K Patra Gyanaranjan Prusty Sarat K Swain

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      PMMA/clay nanocomposites were synthesized by ultrasound assisted emulsifier-free emulsion polymerization technique. Ultrasound waves of different power and frequencies were applied to enhance the dispersion of the clay layers with polymer matrix. The structural information of the synthesized materials was studied by X-ray diffraction (XRD) and it was revealed that the interlayer spacing increased with clay loading. The magnitude of dispersion of the clay in the polymer matrix was detected by transmission electron microscopy (TEM). The Young’s modulus, breaking stress, elongation at break, toughness, yield stress and yield strain of the nanocomposites as a function of different clay concentrations and ultrasonic power were measured. Particle diameter of the nanocomposites was measured by laser diffraction technique. Oxygen permeability of the samples was studied and it was found that the oxygen flow rate was reduced by the combined effect of clay loading and ultrasound. The flame retardant property of the nanocomposites due to clay dispersion was investigated by measurement of limiting oxygen index (LOI).

    • Application of aromatization catalyst in synthesis of carbon nanotubes

      Song Rongjun Yang Yunpeng Ji Qing Li Bin

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      In a typical chemical vapour deposition (CVD) process for synthesizing carbon nanotubes (CNTs), it was found that the aromatization catalysts could promote effectively the formation of CNT. The essence of this phenomenon was attributed to the fact that the aromatization catalyst can accelerate the dehydrogenation–cyclization and condensation reaction of carbon source, which belongs to a necessary step in the formation of CNTs. In this work, aromatization catalysts, H-beta zeolite, HZSM-5 zeolite and organically modified montmorillonite (OMMT) were chosen to investigate their effects on the formation of multi-walled carbon nanotubes (MWCNTs) via pyrolysis method when polypropylene and 1-hexene as carbon source and Ni2O3 as the charring catalyst. The results demonstrated that the combination of those aromatization catalysts with nickel catalyst can effectively improve the formation of MWCNTs.

    • On conduction mechanism in paramagnetic phase of Gd based manganites

      S Sagar M R Anantharaman

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      Materials belonging to the family of manganites are technologically important since they exhibit colossal magneto resistance. A proper understanding of the transport properties is very vital in tailoring the properties. A heavy rare earth doped manganite like Gd0.7Sr0.3MnO3 is purported to be exhibiting unusual properties because of smaller ionic radius of Gd. Gd0.7Sr0.3MnO3 is prepared by a wet solid state reaction method. The conduction mechanism in such a compound has been elucidated by subjecting the material to low temperature d.c. conductivity measurement. It has been found that the low band width material follows a variable range hopping (VRH) model followed by a small polaron hopping (SPH) model. The results are presented here.

    • Electrical and magnetic properties of (BiNa)1/2(FeV)1/2O3

      S K Bera Subrat K Barik R N P Choudhary P K Bajpai

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      Potential multiferroic material, (BiNa)1/2(FeV)1/2O3, synthesized using solid-state route is investigated. The phase formation was confirmed by X-ray diffraction and surface morphology by scanning electron microscopy (SEM). Structural data reveal the single phase formation corroborated by SEM. The grain distribution is uniform with an average grain size of 3.6 𝜇m. Electrical properties were investigated in a frequency range (1 kHz–1 MHz) by complex impedance spectroscopy (CIS) technique. The material showed negative temperature coefficient of resistance (NTCR) reflecting semiconductor behaviour. A.C. conductivity was found to obey Johnscher’s law. Conductivity mechanism is discussed and activation energy estimated (1.17 eV) for the conduction process is associated with Fe3+ → Fe2+ variable state. The M–H curve showed the presence of ferromagnetism in the studied material.

    • Barrier characteristics of Pt/Ru Schottky contacts on 𝑛-type GaN based on 𝐼–𝑉–𝑇 and 𝐶–𝑉–𝑇 measurements

      N Nanda Kumar Reddy V Rajagopal Reddy

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      We have investigated the current–voltage (𝐼–𝑉) and capacitance–voltage (𝐶–𝑉) characteristics of Ru/Pt/𝑛-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/𝑛-GaN Schottky diode are 0.73 eV and 1.4 at 420 K, 0.18 eV and 4.2 at 100 K, respectively. The zero-bias barrier height ($\Phi_{\text{b}0}$) calculated from 𝐼–𝑉 characteristics is found to be increased and the ideality factor (𝑛) decreased with increasing temperature. Such a behaviour of $\Phi_{\text{b}0}$ and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at themetal/semiconductor interface. The current–voltage–temperature (𝐼–𝑉–𝑇) characteristics of the Ru/Pt/𝑛-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ($\bar{\Phi}_{\text{b}0}$) of 1.001 eV and 0.4701 eV and standard deviations ($\sigma_{0}$) of 0.1491 V and 0.0708 V, respectively. The modified ln($J_{0}/T^{2}$) − ($q^{2}\sigma^{2}_{0}/2k^{2}T^{2}$) vs 10$^{3}/T$ plot gives $\bar{\Phi}_{\text{b}0}$ and Richardson constant values as 0.99 eV and 0.47 eV, and 27.83 and 10.29 A/cm2K2, respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the 𝐼–𝑉 and 𝐶–𝑉 methods has been attributed to the existence of Schottky barrier height inhomogeneities.

    • High temperature C/C–SiC composite by liquid silicon infiltration: a literature review

      Manish Patel Kumar Saurabh V V Bhanu Prasad J Subrahmanyam

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      The ceramic matrix carbon fibre (CMC) reinforced composite has received great attention for use in aerospace engineering. In aerospace, the atmosphere is highly oxidative and experiences very high temperature. In addition to this, the materials require high thermal stability and high abrasion resistance in that atmosphere. The C/C–SiC composite meets with these requirements. In this paper, the C/C–SiC composite by liquid silicon infiltration is reviewed thoroughly.

    • Humidity sensing behaviour of polyaniline/magnesium chromate (MgCrO4) composite

      T Machappa M V N Ambika Prasad

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      in situ’ polymerization of polyaniline (PANI) was carried out in the presence of magnesium chromate (MgCrO4) to synthesize PANI/ceramic (MgCrO4) composite. These prepared composites were characterized by XRD, FTIR and SEM, which confirm the presence of MgCrO4 in polyaniline matrix. The temperature dependent conductivity measurement shows the thermally activated exponential behaviour of PANI /MgCrO4 composites. The decrease in electrical resistance was observed when the polymer composites were exposed to the broad range of relative humidity (ranging between 20 and 95% RH). This decrease is due to increase in surface electrical conductivity resulting from moisture absorption and due to capillary condensation of water causing change in conductivity within the sensing materials. PANI / MgCrO4 composites are found to be sensitive to low humidity ranging from 20 to 50% RH.

    • Correlation between diffraction and viscosity data for Bi–Ga molten alloys

      S Mudry A Yakymovych I Shtablavyi V Sidorov K Shunyaev

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      Structure of Bi100−𝑥Ga𝑥 molten alloys containing 38.5, 50, 70 and 91.5 at.% Ga has been studied by means of X-ray diffraction method and compared with viscosity measurements data. Significant changes in the structure factor profile were observed in vicinity of the concentration 70 at.% Ga. The dynamic viscosity coefficient was calculated by use of a statistical atomic distribution model and a Born–Green kinetic theory. The concentration dependence of viscosity is in agreement with change of structure parameters obtained from diffraction data.

    • Influence of heat treatment on microstructure and passivity of Cu–30Zn–1Sn alloy in buffer solution containing chloride ions

      U Tabrizi R Parvizi A Davoodi M H Moayed

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      Tin as an alloying element is of great interest in brasses for dezincification impediment. In this paper, Cu–30Zn–1Sn alloy was submitted to three different heat treatments, viz. A (heating up to 800 °C for 20 h, held at 200 °C for 20 h in salt bath and air cooled), B (heating up to 800 °C for 20 h and water quenched) and C (heating up to 600 °C for 20 h and water quenched). The influence of heat treatment on microstructure was evaluated by OM and SEM–EDS analysis. The corrosion resistance in buffer solution (pH 9), H3BO3/Na2B4O7.10H2O, with various concentrations of chloride ions was evaluated by potentiodynamic polarization curves and compared with multicomponent Pourbaix diagrams. A correlation between the heat treatment, microstructure and passivity of the heat treated samples was observed. The results indicated that all heat treatment procedures led to formation of 𝛼, and 𝛾-Sn-rich phases as microstructure constituents with a small fraction of 𝛽' phase in A. Sn-rich phase appears in grain boundaries and its morphology was slightly changed due to heat treatment. Beneficial influence of low concentration chloride ions on passivity was associated with the formation of copper oxides/hydroxide and chloride complexes. Deterioration was observed at concentrations higher than 0.05 M NaCl due to accelerated dissolution of copper by formation of CuCl$^{−}_{2}$. As a result of dezincification process, preferential corrosion attack and copper redeposition on 𝛼 phase (matrix) were observed. However, Sn-rich (𝛾1) phase in grain boundaries was not attacked due to SnO2 formation. In buffer solution, the higher passivity current density in A was related to the presence of small amount of 𝛽' phase. On the other hand, in 1 M NaCl, lower critical current density for passivation in B and A (about two times lower than C) was attributed to the grain size effect.

    • Synthesis of boron nitride from boron containing poly(vinyl alcohol) as ceramic precursor

      M Das S Ghatak

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      A ceramic precursor, prepared by condensation reaction from poly(vinyl alcohol) (PVA) and boric acid (H3BO3) in 1:1, 2:1 and 4:1 molar ratios, was synthesized as low temperature synthesis route for boron nitride ceramic. Samples were pyrolyzed at 850°C in nitrogen atmosphere followed by characterization using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).

    • EXAFS investigations on PbMoO4 single crystals grown under different conditions

      A K Poswal D Bhattacharyya S N Jha Sangeeta S C Sabharwal

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      Extended X-ray absorption fine structure (EXAFS) measurements on PbMoO4 (LMO) crystals have been performed at the recently-commissioned dispersive EXAFS beamline (BL-8) of INDUS-2 Synchrotron facility at Indore, India. The LMO samples were prepared under three different conditions viz.

      1. grown from a stoichiometric starting charge in air ambient,

      2. grown from a stoichiometric starting charge in argon ambient and

      3. grown from PbO-rich starting charge in air ambient.

      The EXAFS data obtained at both Pb 𝐿3 and Mo K edges of LMO have been analysed to determine Pb–O, Pb–Mo and Mo–O bond lengths in the crystals. The information thus obtained has been used to examine the microscopic defect structures in crystals grown under different conditions.

    • Analysis on insulator–metal transition in yttrium doped LSMO from electron density distribution

      S Israel S Saravana Kumar R Renuretson R A J R Sheeba R Saravanan

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      Yttrium doped LSMO (La1−𝑥Sr𝑥MnO3) was prepared using sol–gel technique and analysed for the insulator–metal transition fromcharge density variation in the unit cell with respect to different stoichiometric inclusion of yttrium. X-ray powder diffraction profiles of the samples were obtained and the well known Rietveld method and a versatile tool called maximum entropy method (MEM) were used for structural and profile refinement. The charge density in the unit cell was constructed using refined structure factors and was analysed. The charge ordering taking place in the insulator–metal transition was investigated and quantified. The insulator–metal transition was found to occur when 20% of La/Sr atoms were replaced by yttrium. The changes in the charge environment have also been analysed.

    • Synthesis and luminescence properties of Eu2+-activated Ca4Mg5(PO4)6 for blue-emitting phosphor

      Liu Min Tang Wanjun Deng Kejian

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      Ca4Mg5(PO4)6:Eu2+ blue-emitting phosphor was synthesized by the combustion-assisted synthesis method under reductive atmosphere. The products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum. XRD analysis confirmed the formation of Ca4Mg5(PO4)6 pure phase. Photoluminescence results showed that the phosphor can be excited efficiently by UV light range from 230–400 nm, and then exhibited bright blue light with peak wavelength at 431 nm. It is a very promising candidate as a blue-emitting phosphor for potential applications in display devices.

    • Synthesis and properties of 𝑁, 𝑁, 𝑁'-tris-(2-ethoxy-naphthalenen-1-yl)−𝑁, 𝑁, 𝑁' triphenylbenzene 1, 3, 5-triamine for dye sensitized solar cell

      Siji Mathew Karickal R Haridas

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      New starburst ethoxy naphthylamine is synthesized using multi-step organic reactions. The synthesized compound is characterized using UV-Visible, FT–IR and NMR spectrometric techniques. The thermal and electrochemical property of the compound was studied using DSC and cyclic voltammetry. Using this compound and a natural dye, organic dye sensitized solid state solar cell was fabricated and the performance analysed.

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