A. K. Himanshu

Synthesis and Dielectric Studies of Polyaniline‐Polyacrylamide Conducting Polymer Composites

The intrinsically conducting polymer, polyaniline (PANI) has been synthesized by chemical polymerization process with the help of water‐soluble support polymer acrylamide (AAm). The dielectric measurement of PANI‐PAAm was measured in the temperature range from 303–393 K at frequency 10 kHz. The temperature dependent data has been analyzed in the framework of dielectric permittivity, loss tangent and ac conductivity. The weak temperatures dependence of PANI‐PAAm (below 340 K) is seen, which is an interesting property with respect to technological applications of PANI‐PAAm as an electro‐inactive material around room temperature.

Electric Modulus Studies of Low Energy Ar9+Irradiated Conducting Polymer PANI‐PVA

Polyaniline (PANI) prepared using water soluble support polymer polyvinyl alcohol (PVA) was subjected to irradiation with 150 keV Argon (Ar9+) ion at the fluence of 7.68×1014 ion/cm2 with beam current of 2 μA (electrical). There has been implantation of Ar atoms. The field dependence of electric modulus response has been measured in a frequency range from 100 Hz to 1 MHz and in a temperature range from room temperature to the glass transition. Ar9+ implantation in PANI‐PVA shifts the peak maximum to the lower frequency. Resistivity analysis earlier showed a decrease in the localization length as well as increase in the energy gap due to the scission of bonds by the energy deposited by Ar9+ ions.

Optical and electronic structure studies of half metallic in Sr2CoWO6 double perovskite

The density function theory (DFT) under the generalised gradient approximation has been used to investigate the electronic structure of the double perovskite half metallic Sr2CoWO6 synthesied by the solid state reaction technique. The band gap of the system was measured from the Uv-Vis spectra and compared with the theoretically calculated values. Our results states that Sr2CoWO6 material behaves as insulators for the spin-up orientation and spindown orientation as found for the half metallic systems.

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.

Dielectric Studies of Ba Substitution in Lead Zinc Niobate-Lead Zirconium Titanate Ceramics by Precipitation Method

The polycrystalline samples of (Pb0.90Ba0.10) [(Zn1/3Nb2/3)0.20-(Zr0.51Ti0.49)0.80]O3 [PBZN-PZT] compositions ceramics have been synthesized by substitution of barium in PZN-PZT by precipitation method and finally by modified columbite method. X-ray diffraction (XRD) analysis of (Pb0.90Ba0.10)(Zn1/3Nb2/3)O3 (PBZN) and PBZN-PZT shows a cubic and mixed phase of tetragonal and rhombohedral pure perovskite structure at room temperature. The dielectric dispersion of the solid solutions of PBZN-PZT has been studied as a function of temperature for the frequency range from 100 Hz to 1 MHz. The temperature (T) variation of the real components (ϵ′) at different frequencies of the dielectric permittivity shows a broad maximum. The diffuse peaks in permittivity versus temperature confirm the relaxor behaviour of PBZN-PZT. The frequency dependence of maximum temperature (T m) in these compounds with barium substitution is modeled using Vogel-Fulcher relation.

Electronic structure calculation of Sr2CoWO6 double perovskite using DFT+U

Using the synchrotron and Raman spectroscopy we measured the lattice parameter and Raman modes of the half-metallic (HM) Sr2CoWO6 (SCoW) synthesied by the solid state reaction technique.. The physical properties of SCoW are studies within the framework of density function theory (DFT) under the generalised gradient approximation (GGA) of Perdew, Bruke, and Ernzerhof both by itself and including a coulomb repulsion via the Hubbard approach or GGA+U. Our results states that Sr2CoWO6 material behaves as insulators for the spin-up orientation and spindown orientation as found for the half metallic systems and at U = 0.06eV the ground state of spin up channel being insulating with spin gap of 2.27eV comparable to the experimental Band gap (BG).Using the synchrotron and Raman spectroscopy we measured the lattice parameter and Raman modes of the half-metallic (HM) Sr2CoWO6 (SCoW) synthesied by the solid state reaction technique.. The physical properties of SCoW are studies within the framework of density function theory (DFT) under the generalised gradient approximation (GGA) of Perdew, Bruke, and Ernzerhof both by itself and including a coulomb repulsion via the Hubbard approach or GGA+U. Our results states that Sr2CoWO6 material behaves as insulators for the spin-up orientation and spindown orientation as found for the half metallic systems and at U = 0.06eV the ground state of spin up channel being insulating with spin gap of 2.27eV comparable to the experimental Band gap (BG).

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

Ab initio study of double perovskites Ba2DySbO6

First principle study of the electronic band structure of Ba2DySbO6 synthesied by the solid state reaction technique have been performed within the framework of density function theory using WIEN2K. It has been shown in the absence of electron-electron interaction (U=0), BaDySO6 behaves like a half-metal. Even in the presence of DFT+U, electron-electron interaction via the Hubbard term (from U = 0, 2.72e -7.02eV), it still shows half metals.

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.