S. K. Bandyopadhyay

X-Ray Photoelectron Spectroscopy Study of Oxygen and Argon Annealed YBa2Cu3O7-δ

X-ray Photoelectron Spectroscopy (XPS) measurements have been performed on oxygen- and argon-annealed YBa2Cu3O7-δ (YBCO) and the results are compared with similar measurements performed on Y2O3. The structural changes in oxygen- and argon-annealed YBCO are reflected in the shift of the Binding Energy (BE) peak positions for the various components existing in the YBCO lattice.

FRACTAL CHARACTERIZATION OF ULTRASONIC SIGNALS FROM POLYCRYSTALLINE MATERIALS

For the first time the concept of fractal geometry is introduced to characterize discrete time domain ultrasonic signals scattered from polycrystalline materials aluminium and brass using the pulse echo method. The fractal dimension of these scattered signals was evaluated using the box counting method and power spectral method. These signals possess unique fractal dimension which remains invariant with the change in sampling rate of signal capturing. The fractal dimension evaluated by the above two methods remains constant in case of aluminium but gives remarkably different values for brass. This observation is interpreted on the basis of the variation of scattering mechanism in these two materials.

Phase transitions in double perovskite Sr2ScSbO6: An Ab-initio study

First Principles study of the electronic properties of recently synthesized double perovskite Sr2ScSbO6 have been performed using density functional theory. With increasing temperature, the Sr compound undergoes three structural phase transitions at 400K, 550K and 650K approximately, leading to the following sequence of phases: P21/n → I2/m → I4/m → Fm-3m. Starting from the monoclinic phase P21/n at room temperature, resulting from the Sc/Sb ordering, the electronic structure for the tetragonal I4/m at 613K and cubic Fm-3m for T≥660K has been studied in terms of the density of states and band-structure. Presence of large band gap, both direct and indirect, has been reported and analyzed.

Electronic structure of ordered double perovskite Ba2CoWO6

Ba2CoWO6 (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200 °C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225) with the lattice parameter, a = 8.210. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, it’s value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states.

High capacitance in BiFeO3 nanorod structure

A remarkably high value of specific capacitance of 450 F/g is observed through electrochemical measurements in the electrode made of multiferroic Bismuth Ferrite (BFO) in the form of nanorods protruding out. These were developed on porous Anodised Alumina (AAO) templates using wet chemical technique. Diameters of nanorods are in the range of 20–100 nm. The high capacitance is attributed to the nanostructure. The specific capacitances are constant after several cycles of charge-discharge.

Optical and electronic properties of double perovskite Ba2ScSbO6

Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Riedvelt analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy to be 4.2eV. A detailed study of the electronic properties has also been carried out using the Full-Potential Linear Augmented Plane Wave (FPLAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications, such as dielectric resonators and filers in microwave applications

High value of ferroelectric polarization in BFO nanorods

Significantly high value of polarization is obtained in multiferroic Bismuth Ferrite (BFO) in form of nanorods protruding out. These were developed on porous Anodised Alumina (AAO) templates using wet chemical technique. Diameters of nanorods vary in the range from 10–100 nm. The high value of polarization is attributed to the nanostructure. There is no leakage current in P-E loop observed at various fields and frequencies.

A FRACTAL BASED MODEL FOR THE CHARACTERIZATION OF THE INTERFACE IN TWO PHASE POLYCRYSTALLINE MATERIALS USING ACOUSTIC MEANS

A model is proposed which investigates the structure of the interface separating two different phases in polycrystalline materials using acoustic waves. This model evaluates the expression for the intensity of the scattered acoustic waves in terms of the wave vector and correlates the observed intensity with the irregularities present on the interface. The concept of fractal dimension has been introduced to differentiate and characterize the irregularities of the interface.