• Volume 27, Issue 1

February 2004,   pages  1-84

• Theoretical approaches to superionic conductivity

Recent theoretical approaches to the understanding of superionic conductivity in polycrystalline, glassy and polymeric materials are briefly reviewed. Phase transitions to the superionic conducting state in the AgI family are apparently triggered by cluster formation and strong mobile ion interaction within the clusters. Anomalous conductivity and related physical properties are explained in the cluster induced distortion model. Ionic composites such as AgX : Al2O3 (𝑋 = Cl, Br and I) involve conducting and non-conducting phases and the all-important interface between the two whose space charge enhances the conductivity and also trigger phase transitions to exotic polymorphic phases, for which the mechanisms are yet to be explored. Ion hopping dynamics controls the conductivity of superionic glasses. Mode coupling and jump relaxation theories account for the non-Debye relaxation observed in a.c. conductivity of these glasses. The theory of conductivity in polymer electrolytes-still in its infancy-involves their complex structure and glass transition behaviour. Preparative and thermal history, composition and crystallinity control ionic conductivity. New approaches to the synthesis of optimal polymer electrolytes such as rubbery electrolytes, crystalline polymers and nanocomposites must be considered before achieving a comprehensive theoretical understanding.

• Synthesis and structural characterization of (Bi2O3)1–𝑥 (Y2O3)𝑥 and (Bi2O3)1–𝑥 (Gd2O3)𝑥 solid solutions

Solid solution series, (Bi2O3)1–𝑥 (Y2O$_3)𝑥 and (Bi2O$_3)1–𝑥 (Gd2O$_3)𝑥, for 𝑥 = 0.10, 0.20, 0.30 and 0.40 were synthesized by standard ceramic technique. The structural phase characterization was carried out using X-ray powder diffraction technique. It was found that the solid solution containing 20–40 mole% of Y2O3 had face-centred cubic structure. All samples of the solid solution series, (Bi2O3)1–𝑥 (Gd2O3)𝑥, had rhombohedral single phase in the concentration range 0.10 ≤ 𝑥 ≤ 0.40. Lattice parameters of fcc phase of Y2O3 doped samples were calculated from the X-ray diffraction data. The lattice constant `𝑎’ gradually decreases with increasing content of dopant concentration (𝑥) for the Y2O3 doped system and obeys Vegard’s rule. The unit cell parameters for the (Bi2O3)1–𝑥 (Gd2O3)𝑥 doped samples showing rhombohedral phase were obtained on hexagonal setting. • X-ray diffraction studies of NbTe2 single crystal NbTe2 is a member of transition metal dichalcogenide (TMDC) group. Single crystals of niobium ditelluride (NbTe2) have been grown by a chemical vapour transport technique using iodine as transporting agent. The composition of the grown crystals was confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray diffraction (XRD) studies. Lattice parameters, volume and X-ray density have been carried out for the grown crystals. The particle size for a number of reflections has been calculated using Scherrer’s formula. • Synthesis and structural characterization of CsNiP crystal CsNiP crystals were synthesized by hydrothermal technique and characterized by the X-ray diffraction method. This alkaline transition metal phosphide crystallizes in the hexagonal system with space group P6$_3/mmc\$ and cell parameters, 𝑎 = 7.173(2) Å, 𝑐 = 5.944(9) Å, 𝑉 = 264.87(7) Å3 and 𝑍 = 2. The final residual factor is 𝑅1 = 0.0362 for 206 reflections with 𝐼 &gt; 2𝜎(𝐼).

• X-ray structure determination and analysis of hydrogen interactions in 3,3′-dimethoxybiphenyl

The crystal structure of 3,3′-dimethoxybiphenyl has been determined by X-ray diffraction methods with an aim of describing the hydrogen interaction in biphenyl derivatives. The title compound crystallizes in monoclinic space group 𝑃21/𝑐 with unit cell dimensions, 𝑎 = 7.706(1), 𝑏 = 11.745(2), 𝑐 = 12.721(2) Å, 𝛽 = 92.31(1)°, 𝑍 = 4 and its structure has been refined up to the reliability index of 3.8%. The average torsion angle about the inter-ring C–C bond is 37.5°. The O1 and O1′ atoms of the methoxy group are deviated by 0.046(1) Å and 0.234(1) Å from the mean planes of respective rings. The crystal cohesion is pronounced due to three-inter-molecular C–H…O hydrogen bonds.

• Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (𝑉B) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (𝐻) and Young’s modulus (𝑌) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100–250 V. Films deposited at |𝑉B| = 250 V exhibited hardness as high as 3300 kg/mm2. This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure.

• Nonlinear 𝐼–𝑉 characteristics study of doped SnO2

When tin oxide is doped with Sb2O3 and CoO, it shows highly nonlinear current (𝐼)–voltage (𝑉) characteristics. Addition of CoO leads to creation of oxygen vacancies and helps in sintering of SnO2. Antimony oxide acts as a donor and increases the conductivity. The results are nearly the same when antimony oxide is replaced by tantalum oxide. The observed nonlinear coefficient, 𝛼 = 30 and the breakdown voltage is 120 V/mm.

• Forbidden reflections from the aramid PPTA—A novel correlation with stacking faults

The occurrence of space group forbidden reflections in the X-ray diffraction patterns from the aramid PPTA has been correlated with the presence of stacking faults. The fraction of sample affected by the presence of such faults has also been estimated.

• Preparation and study of conductivity in lithium salt complexes of mixed MEEP : PEO polymer electrolytes

Poly(ethylene oxide)–LiX complexes and poly[bis(methoxy ethoxy ethoxide) phosphazene]–LiX complexes of polymer thin films were prepared. Conductivity measurements were carried out and the values were found to lie between 10-8 and 1.7 × 10-5 (S/cm). MEEP : LiX salts showed higher conductivity than PEO–LiX salts despite lower dimensional stability. For enhancing stability and conductivity, MEEP–PEO : (LiX)𝑛 systems were prepared and conductivity measurements carried out. Further the MEEP/PEO : (LiX)𝑛 was doped with Al2O3 and TiO2 nanocomposite ceramic fillers and the conductivity was studied. The conductivity vs temperature plots showed the enhancement of conductivity with TiO2 added nanocomposite ceramic fillers. The enhanced conductivity is explained on the basis of the effect of local structural modification-promoting localized amorphous region-for enhancement of the Li+ ion transport.

• A fresh study of optical and thermal properties of polystyrene solutions

Polymers have immense practical applications and one such polymer is polystyrene. It is a linear polymer and useful for plastic optical components. The optical and thermal properties of polystyrene solutions are investigated in this paper making use of the ultrasonic velocity and fluid parameters. The results reveal a number of significant informations.

• X-ray diffraction line profile analysis for defect study in Zr–2.5% Nb material

The microstructure characterization by X-ray line profile analysis is possible for determination of dislocation density, micro-strain within grains due to dislocation and average coherent domain size (subgrain) within the grain. This study presents the X-ray diffraction peaks shape analysis and their broadening with different thermal treatments in Zr–2.5% Nb pressure tube material. The peak shape is analysed using Fourier transformation and information about coherent domain size, micro-strain and dislocation density could be obtained from the Fourier coefficients of the peak. Analysis of broadening of the peaks by integral breadth method also gives the coherent domain size, dislocation density and micro-strain present in the material. The results from the X-ray techniques are comparable to those obtained from direct observation of transmission electron microscopy. The measured yield strength increases with dislocation density. An empirical relationship is obtained for the yield strength from the dislocation density of the material. The measured strength is in agreement with the one calculated from dislocation density.

• Thermal conductivity of Cu–4.5 Ti alloy

The thermal conductivity (TC) of peak aged Cu–4.5 wt% Ti alloy was measured at different temperatures and studied its variation with temperature. It was found that TC increased with increasing temperature. Phonon and electronic components of thermal conductivity were computed from the results. The alloy exhibits an electronic thermal conductivity of 46.45 W/m.K at room temperature. The phonon thermal conductivity decreased with increasing temperature from 17.6 at 0 K to 1.75 W/m.K at 298 K, which agrees with literature that the phonon component of thermal conductivity is insignificant at room temperature.

• Fabrication of silicon based glass fibres for optical communication

Silicon based glass fibres are fabricated by conventional fibre drawing process. First, preform fabrication is carried out by means of conventional MCVD technique by using various dopants such as SiCl4, GeCl4, POCl3, and FeCl3. The chemicals are used in such a way that step index single mode fibre can be drawn. The fibre drawing process consists of various steps such as heating the preform at elevated temperature, diameter monitor, primary and secondary coating, and ultra violet radiation curing. The fibres are then characterized for their geometrical and optical properties. The drawn fibre has diameter of core and cladding to be 8.3 𝜇m and 124.31 𝜇m, respectively whereas non-circularity is found to be 4.17% for core and 0.26% for cladding as seen from phase plot. Mode field diameter is found to be 8.9 𝜇m and 9.2 𝜇m using Peterman II and Gaussian method, respectively. The fabricated fibres showed the signal attenuation of 0.35 dB/km and 0.20 dB/km for 1310 nm and 1550 nm, respectively as measured by the optical time domain reflectometer (OTDR).

• Simulation studies of atomic resolution X-ray holography

X-ray holography is a new method of structure determination based on measurement of interference of a known reference wave with an unknown object wave (containing information on atomic sites scattering the reference wave) so that phase information is preserved. Unlike X-ray diffraction, it does not demand for translational periodicity in the material. It is based on the idea similar to that of optical holography and has been tested on crystals, quasicrystals, thin films and doped semiconductors for their structure determination. In order to analyse potentials and limitations of this technique, we have carried out theoretical simulation studies on simple structures. In this paper we describe the basic algorithm of hologram generation and reconstruction of atomic positions from generated data. We illustrate this technique using Fe (bcc) single crystal as sample case to demonstrate its capabilities and limitations. Simulations were carried out on the Cu (fcc) structure and on complex structure such as the Al–Pd–Mn quasicrystal. Technical issues such as low signal to noise ratio, twin image problem etc have been discussed briefly to emphasize the need for high intensity X-ray source such as synchrotron for experiments and proper reconstruction algorithm. Finally the scope and potential of this technique have been discussed.

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