J. Siva Kumar

Electrical breakdown studies in didymium oxide thin films

Abstract I–V characteristics of sandwiched Al-didymium oxide-Al structures are studied for different thicknesses. The breakdown voltage increases and the dielectric strength decreases with increase of film thickness. Optical photomicrographs of the breakdown patterns during different stages of dc voltage are taken and the results discussed.

Mixed alkali effect in the physical and optical properties of xK2O-(25-x)Na2O-12.5MgO-12.5BaO-50B2O3 glasses

Abstract Borate glasses with the composition xK2O-(25-x)Na2O-12.5MgO-12.5BaO-50B2O3 (x = 0, 5, 10, 15, 20 and 25 mol%) were prepared by the melt-quenching technique and were characterized using X-ray diffraction at room temperature. From the optical absorption spectra, the direct forbidden, direct allowed, indirect allowed, and indirect forbidden energy gaps; Urbach energy; refractive index (n); dielectric constant (ɛ); reflection loss (R); molar refraction (Rm); and molar polarizability (αm) values of all of the glass samples were evaluated. Rm, αm and Λth increase with the increase of the K2O content. The values of R, ɛ and n increase up to x = 10 mol% and then decrease above x = 10 mol%, which may be due to the mixed alkali effect. The density and molar volume values show the opposite behaviour and vary nonlinearly with the K2O content, which manifests the mixed alkali effect in the present glass system. The infrared (IR) spectra of the borate glasses reveal the existence of 3- and 4-coordinated boron atoms. The specific vibrations of the Na-O, K-O, Mg-O, and Ba-O bonds were observed in an IR study.

Preparation and characterization of lithium ion conducting polymer electrolytes based on a blend of poly(vinylidene fluoride-co-hexafluoropropylene) and poly(methyl methacrylate)

Ion conducting polymer electrolytes composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), poly(methyl methacrylate) (PMMA) and lithium triflate (LiTf) were prepared using the solution casting method. Structural change and complex formation in the blend electrolyte systems were confirmed from the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) studies. Thermal properties of the samples were investigated by the differential scanning calorimetry (DSC) technique. The ionic conductivity of these polymer electrolytes was studied by impedance spectroscopy at various temperatures ranging from 303–393 K. The results reveal that the ionic conductivity of the polymer blend electrolytes depends on the PVdF-HFP:PMMA composition as well as the temperature. Maximum room temperature conductivity of 7.4×10−5 S cm−1 was achieved with 22.5 wt.% PMMA. The blending of PVdF-HFP with PMMA improved the thermal stability and ionic conductivity of the polymer electrolyte. Estimated transference numbers suggest the charge transport is predominantly ionic.

FTIR Spectroscopic and DC Ionic conductivity Studies of PVDF-HFP: LiBF4: EC Plasticized Polymer Electrolyte Membrane

In the present paper; the FTIR and Temperature dependent DC Ionic conductivity studies of polymer (80 Wt% PVDF-HFP) with inorganic lithium tetra fluoroborate salt (20 Wt% LiBF4) as ionic charge carrier and plasticized with various weight ratios of Ethylene carbonate plasticizer (10 Wt% to 70 Wt% EC) as gel polymer electrolytes. Solution casting method is used for the preparation of plasticized polymer-salt electrolyte films. FTIR analysis shows the good complexation between PVDF-HFP: LiBF4 and the presence of functional groups in the plasticized polymer-salt electrolyte membrane. Also the analysis and results show that the highest DC ionic conductivity of 1.66 × 10−3 SCm−1 was found at 373 K for a particular concentration of 80 Wt% PVDF-HFP: 20 Wt% LiBF4: 40 Wt% EC porous gel type polymer-salt plasticized porous membrane. Increase of temperature results expansion and segmental motion of polymer chain that generates free volume in turn promotes hopping of the lithium ions satisfying Vogel-Tammann-Fulcher equation.

EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu2+ ions

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li2O–xK2O–12.5BaO–12.5MgO–49B2O3–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (Tg). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of

Dielectric properties of Sb2O3 thin film capacitors

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A study of physical and optical absorption spectra of VO2+ ions in potassium and sodium oxide borate glasses

orbital (2B1g) and the site symmetry around Cu2 is tetragonally distorted octahedral. The variation of g|| and A|| as a function of Li2O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu2 ions corresponding to 2B1g → 2B2g transition. From the optical absorption studies the values of the optical band gap (Eopt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α2, β2 and β12 were evaluated.

Structural and transport properties of PVC blend PEG doped with Mg(ClO4)2 solid polymer electrolyte

Abstract The electrical conduction mechanism in mixed polymer films (polyvinyl pyrrolidone plus polyacrylamide) sandwiched between planar aluminum electrodes was investigated. The films were obtained by the solution growth technique. The electrical conduction and current-voltage characteristics were investigated in the temperature range 300–450 K. Hysteresis in the current-voltage characteristics was observed. The results were interpreted in terms of the Poole-Frenkel conduction mechanism.