Volume 18, Issue 5
September 1995, pages 469-636
pp 469-495 September 1995
A review of the state of the art of electrically conducting polymers is presented. Special emphasis is laid on the nature of the doping processes which induce high electrical conductivity in conjugated organic polymers and on the nature of charge carriers such as solitons, polarons and bipolarons produced in them as a result of such processes. Various factors affecting the electrical conductivity of these polymers and the various models proposed to explain charge transport in them are also discussed. The present status of the structure-property relationship in these conducting polymers and the various routes currently pursued to tailor novel conducting polymers are also briefly mentioned. Finally the various applications of these novel electronic materials are described.
pp 497-501 September 1995
The present investigation deals with the synthesis of monolithic NiCl2-silica gels obtained by hydrolysis and polycondensation of tetraethoxy silanes. This sol to gel formation can mainly be controlled by adjusting some variables e.g. acid content of the solution, ageing and leaching times. A minimum acid content was found necessary to prepare uncracked gel while ageing and leaching times were found to be not that sensitive for the formation of uncracked gels.
pp 503-515 September 1995
When mechanically excited, initially the ML intensity increases, attains a maximum value and then decreases with time. The total ML intensityIT initially increases with the impact velocityVo of piston and attains a saturation value for higher values ofVo and follows the relationIT=IToexp(−Vc/Vo) whereITo andVc are constants. The ML intensity is maximum for 20% CdS contents in the (Zn, Cd)S phosphors due to increase in hardness which may in turn increase the fracture stress and subsequently the piezoelectric field strength. The wavelength corresponding to the peak of both the ML and PL spectra shift towards longer wavelength with increasing CdS contents. Some models are discussed and it is concluded that the impulsive deformation of these phosphors may be due to piezoelectrification of newly created surfaces. The similarity of ML spectra with EL and PL spectra suggests that although the excitation processes are different, emission process is governed by the states of similar nature.
pp 517-529 September 1995
Silver clad Bi-2223 tapes with consistently high critical current densities of over 30,000 A/cm2 at 77 K and zero field were prepared by powder-in-tube (PIT) technique. Powder XRD, electron microscopy, a.c. susceptibility and critical current measurements were used to study the phase assemblage, microstructure and transport properties of these tapes at various stages of processing. The precursor powder for PIT process was prepared by a sol-gel route by acrylate method using freshly prepared nitrates of Bi, Pb, Sr, Ca and Cu. The carbon content in the powder was minimized by subjecting it under dynamic vacuum calcination followed by heating in free flow of oxygen for long durations with intermittent grindings. The choice of initial stoichiometry, high reactivity of the precursor, effective removal of carbon, choice of phase assemblage at the filling stage and the multistage thermomechanical processing at optimized conditions were found to be responsible for the high critical current density.
pp 531-539 September 1995
Ultra-thin cobalt silicide (CoSi2) was formed from 10 nm cobalt film by solid phase reaction of Co and Si by use of rapid thermal annealing (RTA). The Ge+ ion implantation through Co film caused the interface mixing of the cobalt film with the silicon substrate and resulted in a homogeneous silicide layer. XRD was used to identify the silicide phases that were present in the film. The metallurgical analysis was performed by RBS. XRD and RBS investigations showed that final RTA temperature should not exceed 800°C for thin (< 50 nm) CoSi2 formation.
pp 541-548 September 1995
The synthesis, spectral, electrical and magnetic properties of charge transfer materials of aromatic diamines namely benzidine (BEN) andρ-toluidine (O.TOL) with various acceptors such as iodine, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), andp-chloranil (p-CA) have been reported. These materials excepto-toluidine-chloranil complex have been found to be typical molecular semiconductors on the basis of temperature dependence on their electrical conductivity. They have low electrical conductivities and two thermal activation energies indicating mixed conductivity mechanism in which both the electrons and holes are charge carriers, one dominating over the other at different temperatures. The observation of the metal like electrical conductivity i.e. the increase of electrical conductivity with decreasing temperature in theo-toluidine-chloranil system is unique for this class of molecular electronic materials.
pp 549-555 September 1995
Crystal sizes and lattice distortion parameters for root, pulse and cereal starch granules have been determined using observed X-ray diffraction reflections by Fourier method. Enthalpy for the formation of the lattice in root, pulse and cereal starches has been estimated and compared. It is found that the crystal size is normally high in root starch compared to pulse and cereal starches.
pp 557-562 September 1995
Stoichiometric polycrystalline tin oxide thin films were deposited by the reactive evaporation of tin and the SnO2 formation was found to be strongly dependent on the deposition parameters. The preferred orientation of the SnO2 films deposited on different substrates was varying due to the dislocation defects arising during the thin film formation. The X-ray diffraction (XRD) studies identified a tetragonal structure while the scanning electron microscopic (SEM) studies revealed a polycrystalline surface for the SnO2 films reactively deposited.
pp 563-576 September 1995
Complex immittance spectra of model equivalent circuits involving resistive and capacitive elements are calculated. A comparison of experimentally obtained complex immittance plots with these diagrams greatly facilitates the search for the most appropriate equivalent circuit representing the electrical properties of electronic ceramics.
pp 577-585 September 1995
65(SrO·TiO2)−35(2SiO2·B2O3) wt% glass was synthesized. Differential thermal analysis study shows one exothermic peak which shifts towards higher temperature with increasing heating rate. Glass ceramics prepared by controlled crystallization of strontium titanate borosilicate glass produce uniform distribution of crystallites in a glassy matrix. Attempt was made to crystallize strontium titanate phase in this glass ceramic. Different phases precipitated out during ceramization have been identified by X-ray diffraction. It appears that due to high reactivity of SrO with B2O3, strontium borate crystallizes as principal phase followed by TiO2 (rutile) and Sr3Ti2O7 phases. Dielectric constant of these glass ceramics was observed to be more or less temperature independent over wide range of temperatures with low values of dielectric constant and dissipation factor.
pp 587-592 September 1995
Ferroelectric and piezoelectric properties ofxPb(Mg1/3Nb2/3)O3−(1−x)Pb (Zr0·55Ti0·45)O3 system have been investigated. X-ray diffraction patterns indicate rhombohedral and cubic structures. Maximum dielectric constant and piezoelectric properties are exhibited by 0·5–0·5 PMN-PZT composition.Pr is high in 0·6–0·4 PMN-PZT composition.
pp 593-597 September 1995
Cerium(III) orthovanadate with a small deviation from stoichiometric composition is ap-type semiconductor between 30 and 800°C. The electrical conduction in cerium(III) orthovanadate is due to thermally activated hopping of holes on equivalent Ce3+-Ce4+ lattice sites. The DTA result of CeVO4 indicated a possible phase transition at about 70°C. The IR spectrum of the sample showed bands at 865 and 810 cm−1, typical of VO4 group of orthovanadates.
pp 599-602 September 1995
A new optical interferometric technique to measure the electrostrictive coefficients of XH2PO4/H3BO3 binaries (where X=Na, K and NH4) is reported. This direct method is found to be advantageous in measuring the positive as well as the negative sign of the electrostrictive coefficients. Design of the apparatus and its merits are discussed. In XH2PO4/H3BO3 binaries the addition of boric acid is found to decrease the value of binary electrostriction coefficient in comparison to their pure samples.
pp 603-621 September 1995
The red mud surface was treated with organosilane, organotitanate and organozirconate coupling agents respectively. The change in the surface was determined by IR spectroscopy and SEM. The effect of coupling agents concentration on the tensile and flexural strength of red mud-filled polyester resin has been studied. The efficacy of these coupling agents was discussed in relation to dispersion of red mud in unsaturated polyester resin and also by measuring performance of finished castings under both dry and wet conditions. It was found that organotitanate treated red mud-filled polyester composite gives better physico-mechanical properties than the control and other coupling agents treated red mud. Fractography of failed samples was also discussed in terms of their mechanical properties.
pp 623-630 September 1995 Rapid Communication
Three independent studies have been reported on the free energy of formation of NiWO4. Results of these measurements are analyzed by the “third-law” method, using thermal functions for NiWO4 derived from both low and high temperature heat capacity measurements. Values for the standard molar enthalpy of formation of NiWO4 at 298·15 K obtained from “third-law” analysis are compared with direct calorimetric determinations. Only one set of free energy measurements is found to be compatible with calorimetric enthalpies of formation. The selected value for ΔfHm0(NiWO4, cr, 298·15 K) is the average of the three calorimetric measurements, using both high temperature solution and combustion techniques, and the compatible free energy determination. A new set of evaluated data for NiWO4 is presented.
pp 631-636 September 1995 Rapid Communication
A novel solid solution in the system Bi-W-Cu-O has been synthesized and its structural and dielectric properties studied. The solid solution Bi2O3-(1 −x)WO3-xCuO exists up tox=0·7; the solid solutions up tox=0·65 are orthorhombic but stabilize in tetragonal structure in a narrow range aroundx=0·7. The solid solutions are non-centrosymmetric and exhibit ferroelectric behaviour similar to their parent phase Bi2WO6. The Curie point of the solid solution is found to decrease with increase inx.
Volume 42 | Issue 6
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