Katta Narasimha Reddy

Synthesis of Some Fused Pyrazoles and Isoxazoles

The α-keto methylene group in 3,5-diaryl-2-cyclohexenones 2 and 3,5-diarylcyclohexanones 8 have been used to obtain fused pyrazoles and isoxazoles. The new compounds were characterized by IR and 1H-NMR spectral data.

Effect of plastic deformation on the thermally stimulated luminescence of NaCl:Y crystals

Abstract The relation between plastic deformation and thermally stimulated luminescence (TSL) in NaCl crystals doped with yttrium has been studied in some detail. Plastic deformation followed by irradiation in these crystals caused the increase in TSL intensity and a shift in peak positions of peak II (70°C) and peak III (130°C) to high temperatures. The defects playing the dominent role in shifting the TSL peaks on deformation are identified. The shifting of peaks to high temperatures on plastic deformation is attributed to the perturbation at the emitting sites caused during the redistribution of defect centres on deforming the crystal.

Effect of substrate temperature on structural and optical properties of nanostructured ZnO thin films grown by RF magnetron sputtering

Nanocrystalline Zinc oxide (ZnO) thin films were prepared by using physical vapor deposition under a vacuum of 5 × 10−5 Torr by using rf magnetron sputtering technique at different substrate temperatures ranging from 373K to 573K. X-ray diffraction analysis (XRD) indicates that the films are polycrystalline, with strong preferential orientation of grains along the c-axis irrespective of their substrate temperature. The microstructural parameters, such as the lattice constant, crystallite size, stress, strain and dislocation density are calculated. The effect of substrate temperature on the deposited films was discussed. The grain size of the deposited ZnO films is observed to be small and is within the range of 11 to 48 nm. The grain size is observed to be increase from 11.72 to 48.52 nm with increasing substrate temperature. Optical measurements indicate the existence of a direct-band gap-allowed optical transition with a corresponding energy gap in the range of 3.26 – 3.32 eV. The films posses high transmittance over 90 % in the visible region and sharp absorption edge near 380 nm.

Structural and optical properties of CdO thin films deposited by RF magnetron sputtering technique

Cadmium oxide (CdO) thin films were deposited on glass substrate by r.f. magnetron sputtering technique using a high purity (99.99%) Cd target of 2-inch diameter and 3 mm thickness in an Argon and oxygen mixed atmosphere with sputtering power of 50W and sputtering pressure of 2×10−2 mbar. The prepared films were characterized by X-ray diffraction (XRD), optical spectroscopy and scanning electron microscopy (SEM). The XRD analysis reveals that the films were polycrystalline with cubic structure. The visible range transmittance was found to be over 70%. The optical band gap increased from 2.7 eV to2.84 eV with decrease of film thickness.

Effect of previous heat treatment on ionic conductivity of yttrium-doped KBr crystals

Abstract Ionic conductivity studies have been carried out on KBr:Y crystals at different temperatures. The conductivity temperature plot of KBr:Y exhibits a well-known three-stage conductivity in the temperature range 100–560 °C. From the analysis of these plots activation energies for the migration of cation vacancies, the formation of Schottky pairs, the association of yttrium ion with a cation vacancy etc. are calculated. The conductivity of KBr:Y after quenching from elevated temperature is found to decrease. This result in comparison with optical absorption results is explained on the basis of formation of impurity vacancy dipoles, precipitates and clusters.

Thermally Stimulated Luminescence Studies in High Temperature Superconductors

Thermally Stimulated Luminescence (TSL) is generally credited as a potentially useful trap level spectroscopic method of investigating materials. The electronic and ionic transport phenomena in solids observed during non-isothermal temperature scans are often studied employing the TSL technique. Though the phenomenon of TSL has been well known for a considerable time, in recent years, interest in TSL has continued to increase, because the phenomena of TSL provide an ultra sensitive micro probe into the solid state.

Some Aspects of Single Crystal Growth of High Temperature Superconductors

The field of high temperature superconductivity has matured considerably during the past four years. Despite of this progress the mechanisms of super conductivity have continued to remain elusive and general characteristics of recently discovered families of high temperature super conductors have shown that we are still far from having an even a satisfactory model of this most exiting phenomena of Solid state materials. Inspite of the fast growth of research in the field of high temperature superconductors(HTSC) the ultimate limits for transition temperature (Tc) in copper oxide based materials are still uncertain. The continued growth of the field now requires careful and well directed studies of various materials and physical issues vital to the understanding and applications of superconductor materials. One of such Important areas of study is the preparation of oxide superconductors in single crystal form. There is an urgent need to quantify the physical and mechanical properties of these materials in order to make sensible judgments on the practical usage of these materials and define their limitations.

Growth of textured films of BiSCCO from alkali halide solutions

Films of Bi-Sr-Ca-Cu-O with lead doping using SrF2 substrates have been grown from KCl solution. The films were highly textured withC-axis perpendicular to the substrate surface. The onset of the resistive transition was at 81 K and zero resistance at 78 K. This technique is permising in view of the possibility to grow large films of both Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Oy phases.