P. Predeep

Crystallization and specific heat studies of Se100 − xSbx (x = 0, 2 and 4) glass

Abstract Bulk glasses of compositions Se 100 − x Sb x ( x = 0, 2 and 4) are prepared by melt quenching technique. Differential scanning calorimetry (DSC) is employed to study the crystallization mechanism as well as specific heat of these glasses. Samples are subjected to thermal scanning in the DSC at various heating rates. All the compositions have shown well defined exothermic peaks of crystallization. The crystallization data are examined in terms of modified Kisingers equation for the activation energy of crystallization. Also the results were analysed using the method suggested specifically for nonisothermal crystallization by Matusita et al . and the activation energy for crystallization and the dimensionality of crystal growth are indicated for all the compositions. It has also been found that the thermal stability of the system is enhanced by the alloying of Se with small atomic percentages of antimony. Specific heat, C p , of all the compositions were also evaluated and discussed.

MAGNETIC BEHAVIOR OF FUNCTIONALLY COATED SUPER-PARAMAGNETIC Ni0.5Cu0.5Fe2O4-POLYPYRROLE NANO-COMPOSITES

This article has been retracted. A statement of retraction is published in Mod. Phys. Lett. B Volume 28, Issue 26 (2014) http://dx.doi.org/10.1142/S0217984914930014

Nanocrystalline Spinel Mn

We have synthesized a series of nanocrystalline ferrite samples with the composition MnxCu1-xFe2O4 (x=0.2, 0.4, 0.6, 0.8) by an advanced sol-gel auto-combustion method. The X-ray diffraction patterns confirm the existence of single-phase cubic spinel crystal structure of ferrites with lattice parameter ranges from 8.395 ? to 8.45 ?. We report the equilibrium radii for tetrahedral and octahedral sites in the unit cells and the estimated cation distribution over the two sites of nanocrystalline MnxCu1-xFe2O4. We also estimate the oxygen positional parameter as 0.389. The positron annihilation life time spectroscopic studies were carried out for all the samples and analyzed the variation of life time parameters ?1; I1, ?2; I2 and the mean life time ?m to elucidate the defect structure of the nanocrystalline MnxCu1-xFe2O4. We found that the overall vacant type defects fill up as the Mn2+ ion concentration, x, increases. The value of ?1 varies from 150 ps to 170 ps and that of ?2 varies from 295 ps to 335 ps, which are the characteristic values for nanocrystalline samples, indicating the presence of intergranular as well as surface-diffused vacancies in the crystal structure.

_{x}

Abstract Addition of copper to the semiconducting glassy system Ge15Te85−xCux (x=2, 4, 5, 6, 8, and 10) at the tellurium site is seen to produce considerable changes in the glass transition temperature (Tg) of the system. For a particular value of copper percentage, the Tg shows a minimum critical value. We have made an attempt to explain the observed variation of Tg with Cu content on the basis of various models like the chemically ordered network model, the constraints theory, the covalent bond approach of Tichy and Ticha and former valence shell (FVS) model proposed by Liu and Taylor.

Cu

Bulk glass of composition Se70Te28Cd2 was prepared by the melt quenching technique. Differential Scanning Calorimetry were performed under isothermal conditions and the results have been analysed using the transformation kinetics theory developed by Johnson-Mehl and Avrami. The results indicate that the crystallization process is a three dimensional growth process. The calculated value of the effective activation energy, EG, for crystal growth, was 173 ± 0.5 kJ/mol for this glass.

_{1 - x}

Recently, it has been reported that prevulcanization of natural rubber (NR) latex does not hinder the formation of conjugated sequences, which is a precondition for developing intrinsic electrical conductivity in polymers. In this article, the authors report for the first time that incorporation of a steric stabilizer such as starch enhances the solution doping of the prevulcanized NR latex resulting in flexible semiconducting thin films with an optimum enhancement in the electrical conductivity behavior and a decrease in optical band gap. However, the characteristic color changes and the insulator-conductor transitions are gradual, indicating a lower doping rate and hence a longer doping period for the system. Moreover, the complexation of the doped iodine (I2) atom with the starch molecule prevents the out-diffusion of I2, and hence imparts stability in the electrical conductivity. The mechanical studies reveal desirable strength for the doped films. The formation of conjugated sequences of double bonds in the poly isoprene (PI) backbone is examined using a UV/VIS and an FTIR-ATR spectroscopy. The swelling studies indicate a reinforcement effect in starch containing composite films at low proportions. The scanning electron micrographs (SEM) of the fabricated films show a compatible phase for the composite and hence a better perfection of the surface.

Fe

Thermal conductivity and thermal diffusivity of three rare earth oxide powders (Gadolinium oxide, Samarium oxide and Yttrium oxide) are measured experimentally using Transient Plane Source (TPS) technique at ambient temperature. An attempt has been made to accommodate the effect of porosity of the powders on thermal conductivity. Calculation of effective thermal conductivity on the basis of a theoretical model has been carried out and it has been found that the theoretical results are in good agreement with the experimental values. Further it has been shown that the TPS technique is an effective method for the measurement of thermal conductivity of powders.

_{2}

Abstract More than three decades after the major breakthrough in the efforts to develop intrinsic electric conductivity in conjugated polymers, which culminated in the year 2000 Nobel Prize for Shi...

O

The thermal behavior of bulk glasses in the Ge20Se80 − xBix(x = 2.5, 4.0, 6.0 at %) system is studied using modulated differential scanning calorimetry (MDSC). All samples have the same thermal history as a result of heating to a temperature above the glass transition point, equilibrating, and then cooling. The total heat flow, modulated heat flow, reversing heat flow, and nonreversing heat flow under heating and cooling schedules are measured. The glass transition temperature Tg, the relaxation enthalpy ΔH, the specific capacity Cp, and the specific heat capacity difference ΔCp = Cpl − Cpg, which characterize the thermal events in the glass transition region, are also determined. These parameters reveal an increase with x, which can be attributed to the increase in the average coordination number with an increase in the bismuth content (at %) in the composite. The ratio of heat capacities Cpl/Cpg, the width of the glass transition temperature range ΔTg, and the activation enthalpy for glass transition ΔHTg are also studied. The values of the ratio Cpl/Cpg vary in the range between 1.038 and 1.112. The activation energy of crystallization is evaluated using the Kissinger, modified JMA, and Matusita equations, which is found to be in the range of 100.92 kJ/mol.

_{4}

Optical energy band gap of nanocrystalline NiCr0.8Fe1.2O4 ferrite have been studied. The nanocrystalline NiCr0.8Fe1.2O4 ferrite have been synthesized using sol‐gel technique. X‐ray diffraction pattern confirms the formation of spinel structure in single phase and the average particle size is 4 nm. The energy band gap measurements of nanocrystalline NiCr0.8Fe1.2O4 ferrite in pellet form have been carried out by absorption spectra using double beam spectrophotometer. A pellet of nanoparticle ferrite was made under a load of 10 tons. From the analysis of absorption spectra, nanocrystalline NiCr0.8Fe1.2O4 ferrite have been found to have energy band gap of 3.2 eV at room temperature.