• Volume 29, Issue 4

      August 2006,   pages  339-420

    • Solution-combustion synthesis of Bi1–𝑥Ln𝑥O1.5 (Ln = Y and La–Yb) oxide ion conductors

      Manjunath B Bellakki A S Prakash C Shivakumara M S Hegde A K Shukla

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      Cubic fluorite related Bi1–𝑥Ln𝑥O1.5 (Ln = Y and La–Yb) phases are synthesized by solutioncombustion method using glycine as the fuel. The cubic fluorite phase is stabilized with 25 mole% of rare earth cations. The lattice parameter of cubic phase increases linearly with size of the lanthanide ion. The synthesized powders are nano-metric in size and exhibit excellent compactability and reach 98% densification even on short period of sintering. The oxides with relatively larger cations Nd, Sm, Eu, Pr and Gd with 25 mole% composition transform to rhombohedral structure while others retain cubic upon sintering. All the phases show high oxide–ion conductivity and the values obtained are in good agreement with the reported values.

    • Impedance and a.c. conductivity studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic prepared through conventional and microwave sintering route

      Syed Mahboob G Prasad G S Kumar

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      Electrical conduction studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic samples prepared through conventional and microwave sintering route are presented in this paper. D.C. and a.c. conductivities of these samples as a function of temperature from 300–900 K have been studied. Two types of conduction processes are evident from the frequency dependant conductivity plots, i.e. low-frequency conduction due to short-range hopping and high-frequency conduction due to the localized relaxation (reorientational) hopping mechanism. Grain and grain boundary contributions to the conductivity in these samples are obtained from impedance/admittance measurements via equivalent circuit modelling.

    • Acoustic study of nano-crystal embedded PbO–P2O5 glass

      Sudip K Batabyal A Paul P Roychoudhury C Basu

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      Nano-crystal embedded PbO–P2O5 glass has been prepared and characterized by XRD and TEM measurements. The ultrasonic velocity and attenuation measured within the temperature range 80–300 K show significant structure and interesting feature with the presence of nano-crystalline region. The glass samples were prepared by melt-quench method and nano-crystals of different sizes were produced by heat treatment of the glasses for different durations of heating. All the processes were carried out at or above glass transition temperature. A theoretical model that takes account of the effects of thermally activated relaxation, anharmonicity as well as microscopic elastic inhomogeneities arising out of fluctuations has been successfully applied to interpret the variation of ultrasonic velocity and attenuation data. An interesting outcome of this application has been to propose a method for the determination of the size of nano-crystals from the ultrasonic attenuation data.

    • Spectroscopic investigations of Cu2+ in Li2O–Na2O–B2O3–Bi2O3 glasses

      N Srinivasa Rao M Purnima Shashidhar Bale K Siva Kumar Syed Rahman

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      Pure and copper doped glasses with composition, 𝑥Li2O–(40–𝑥)Na2O–50B2O3–10Bi2O3, have been prepared over the range 0 < 𝑥 < 40. The electron paramagnetic resonance (EPR) spectra of Cu2+ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, 𝛼2 and 𝛽2, have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO3 and BO4 units in the disordered manner.

    • Rings, chains and planes: Variation of 𝑇g with composition in chalcogenide glasses

      P K Thiruvikraman

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      We propose a microscopic, phenomenological model for the decrease in the viscosity observed at glass transition. Our model is primarily applicable to chalcogenide glasses. According to this model, the decrease in the viscosity at glass transition is mainly due to the breaking of the Van der Waals bonds in the chalcogenides. Using this model, we derive a relationship between the glass transition temperature, 𝑇g, and the molar volume 𝑉m. The validity of this relation is checked using experimental data available in the literature for two binary systems (Ge–Se and As–S) and a pseudo-binary system (As40Se𝑥Te60–𝑥).

    • Optical properties of samarium doped zinc–tellurite glasses

      B Eraiah

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      Glasses with the composition, (Sm2O3)𝑥(ZnO)(40–𝑥)(TeO2)(60), were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz–Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.

    • Studies on conductivity and dielectric properties of polyaniline–zinc sulphide composites

      H C Pant M K Patra S C Negi A Bhatia S R Vadera N Kumar

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      In the present paper, we report electrical conductivity and dielectric studies on the composites of conducting polyaniline (PANI) with crystalline semiconducting ZnS powder, wherein PANI has been taken as inclusion and ZnS crystallites as the host matrix. From the studies, it has been observed that the value of room temperature d.c. conductivity of the composites with volume fraction of PANI > 0.65 shows an unusual behaviour wherein, conductivity values of the composites exceed that of PANI itself with maximum value as high as 6 times that of PANI at the volume fraction of 0.85. A similar trend has also been observed for the real and imaginary parts of complex dielectric constant values of the composites. This unusual behaviour in the d.c. conductivity and dielectric properties has been attributed to the enhancement in the degree of crystallinity of PANI as a consequence of its interfacial interaction with ZnS matrix. The results of optical microscopy show coating of PANI all around the ZnS particles. The temperature dependent conductivity studies suggest the quasi one-dimensional VRH conduction in PANI as well as its composites with ZnS. FTIR and XRD studies have also been reported.

    • Microstructural studies on variation of defect parameters in Zr–Sn alloys and their transition with interchange of solvent and solute in Zr–Ti and Ti–Zr alloy systems by modified Rietveld method and Warren–Averbach method

      J Ghosh S K Chattopadhyay A K Meikap S K Chatterjee

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      The effects of deformation and the transition of microstructural defect states with the interchange of solvent and solute in Ti–Zr and Zr–Ti alloys of six different compositions and Zr–Sn alloys in three different compositions have been investigated by X-ray diffraction line profile analysis. The detailed analysis of the X-ray powder diffraction line profiles was interpreted by Fourier line shape analysis using modified Rietveld method and Warren–Averbach method taking silicon as standard. Finally the microstructural parameters such as coherent domain size, microstrains within domains, faulting probability and dislocation density were evaluated from the analysis of X-ray powder diffraction data of Zr base Sn, Ti and Ti base Zr alloys by modified Rietveld powder structure refinement. This analysis confirms that the growth fault, 𝛽, is totally absent or negligibly present in Zr–Ti, Ti–Zr and Zr–Sn alloy systems, because the growth fault, 𝛽, has been observed to be either negative or very small for these alloy systems. This analysis also revealed that the deformation fault, 𝛼, has significant presence in titanium-base zirconium alloy systems but when zirconium content in the matrix goes on increasing beyond 50%, this faulting behaviour suffers a drastic transition and faulting tendency abruptly drops to a level of negligible presence or zero. This tendency has also been observed in Zr–Sn alloys signifying high stacking fault energy. Therefore, Zr and Zr-base alloys having high stacking fault energy can be used as hard alloys in nuclear technology at high temperature.

    • Influence of nickel addition on magnetic and electro-mechanical behaviour of permalloys

      Kiran Gupta K K Raina S K Sinha

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      Magnetic and electro-mechanical investigations have been carried out in two Ni–Fe permalloys under hydrogen atmosphere by varying annealing temperature. These alloys have been characterized for various magnetic parameters like peak permeability, coercivity and core loss under changed annealing profile conditions. The magnetic properties of Ni-rich (Ni ∼ 82%) alloy at 100 Hz were found to be better than the low Ni (Ni ∼ 47%) alloy. The alloys were tested for watch movement and found that the battery life of the watch movement improved by 38% using Ni-rich permalloy.

    • Dielectric parameters and a.c. conductivity of pure and doped poly (methyl methacrylate) films at microwave frequencies

      Anju Tanwar K K Gupta P J Singh Y K Vijay

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      Dielectric properties of pure and doped poly (methyl methacrylate) (PMMA) films at microwave frequency, 8.92 GHz, have been studied at 35°C. Iodine, benzoic acid and FeCl3 have been used as dopants. The losses in doped films are found to be larger than in pure PMMA films. The increased losses account for increased a.c. conductivity in doped films. The increase in conductivity is accounted due to creation of additional hopping sites for the charge carriers in doped samples. The dielectric data has also been used to evaluate optical constants, absorption index (𝐾) and refractive index (𝑛) of the films.

    • Gas sensing properties of Cu and Cr activated BST thick films

      G H Jain L A Patil

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      H2S gas sensing properties of BST ((Ba0.67Sr0.33)TiO3) thick films are reported here for the first time. BST ceramic powder was prepared by mechanochemical process. Thick films of BST were prepared by screen-printing technique. The sensing performance of the films was tested for various gases. The films were surface customized by dipping them into aqueous solutions of CuCl2 and CrO3 for various intervals of time. These surface modified BST films showed improved sensitivity to H2S gas (100 ppm) than pure BST film. Chromium oxide was observed to be a better activator than copper oxide in H2S gas sensing. The effect of microstructure and amount of activators on H2S gas sensing were discussed. The sensitivity, selectivity, stability, response and recovery time of the sensor were measured and presented.

    • Thermally stimulated discharge conductivity in polymer composite thin films

      V S Sangawar P S Chikhalikar R J Dhokne A U Ubale S D Meshram

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      This paper describes the results of thermally stimulated discharge conductivity study of activated charcoal–polyvinyl chloride (PVC) thin film thermoelectrets. TSDC has been carried out in the temperature range 308–400°K and at four different polarizing fields. Results are discussed on the basis of mobility of activated charcoal and polyvinyl chloride chains.

    • Potentiometric study of polyaniline film synthesized with various dopants and composite-dopant: A comparative study

      P D Gaikwad D J Shirale V K Gade P A Savale K P Kakde H J Kharat M D Shirsat

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      The potentiometric study of polyaniline (PANI) film synthesized with dopants viz. polyvinyl sulfonic acid (PVS), 𝑝-toluene sulfonic acid (𝑝TS), dodecyl benzene sulfonic acid (DBS) and composite-dopants viz. PVS–𝑝TS and PVS–DBS, has been carried out. The synthesized PANI films were characterized by electrochemical technique, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and conductivity measurement. It was found that the PANI doped with PVS gives good electrochemical properties, conductivity as well as surface morphology as compared to 𝑝TS and DBS, whereas in composite dopants the PANI doped with PVS–𝑝TS gives good polymer matrix as compared to PVS–DBS.

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