NOPR Collection:

Bronsted and Lewis acid sites on binary oxides of alumina-yttria

2016-07-20T06:25:54Z

Title: Bronsted and Lewis acid sites on binary oxides of alumina-yttria Authors: Jayasree, J Abstract: Different compositions of alumina-yttria were prepared by coprecipitation technique using aqueous.NH₃. The structure, .surface characteristics and thermal stability of the catalysts were determined by XRD, TGA, DTA, SEM and ESCA. Acid properties of alumina-yttria were investigated by means of infrared spectra of chemisorbed pyriding, MAS ²⁷AI.NMR and Hammett indicators. Catalysts with higher alumina content preferentially showed more octahedral coordination in the lattice. Bronsted acid sites increased with alumina content of the catalyst. Lewis acidity of catalyst samples increased with amount of yttria in the samples. Page(s): 232-236

Pairing mechanism and transition temperature of Ba-Pb-BiO superconductors

2016-07-20T06:25:15Z

Title: Pairing mechanism and transition temperature of Ba-Pb-BiO superconductors Authors: Varshney, Dinesh; Singh, R K; Shah, Sanjay Abstract: The nature of pairing mechanism in cubic perovskite BaPbBiO₃ has been investigated by developing a model potential which involves electron-electron, electron-optical phonon as well as electron- Plasmon interactions. The interaction potential was used to obtain the pairing parameters as coupling strength and. Coulomb repulsive parameter. Coupled oscillations of electronic charge with longitudinal optical phonon describe the superconducting nature of bismuth oxides. Estimated value of coupling strength (λ=0.84) is consistent with a moderate attractive interaction. The screened Coulomb repulsive parameter (µ*=0.22) infers the poor screening of charge carriers with low carrier concentration and reflects a small density of states. The superconducting transition temperature (Tc) of BaPb₀.₇₅ Bi_0.25O₃is evaluated as 15.5 K which is consistent with the earlier reported data. The analysis has led, to the conclusion that weak to moderate coupling exists and the coupling of charge oscillations with longitudinal optical phonon mode could be a reason to the superconductivity in Ba-Pb-BiO superconductors. Page(s): 225-231

Determination of interface state density of metal-semiconductor field effect transistors

2016-07-20T06:24:29Z

Title: Determination of interface state density of metal-semiconductor field effect transistors Authors: Chattopadhyay, P; Majumdar, L Abstract: A method for the determination of the interface state density of a metal-semiconductor field effect transistor is developed which requires an analysis of the temperature dependence of threshold voltage over a certain range of temperature. The method is used to estimate the values of interface state densities of GaAs MESFETs from the available experimental data on threshold voltage in the literature. Page(s): 220-224

Spectral sensitization of sprayed n-ZnO electrode by rose bengal in non-aqueous photoelectrochemical cell

2016-07-20T06:23:28Z

Title: Spectral sensitization of sprayed n-ZnO electrode by rose bengal in non-aqueous photoelectrochemical cell Authors: Bahadur, Lal; Pandey, J P Abstract: Photosensitizing ability of rose bengal was studied at semiconducting n-ZnO electrode in acetonitrile medium using hydroquinone as supersensitizer. In order to ascertain the exclusive effect of dye sensitization on photocurrent at ZnO electrode, studies have been conducted under filtered light (λ > 420 nm) illumination also. Energy level diagram was constructed using redox potentials of rose bengal determined from cyclic voltammetric studies (reduction potential = -0077 V and oxidation potential = + 0.93 V vs SSCE), coupled with the flat-band potential of Zno electrode (V_fb = -0.60±0.02 V vs SSCE) determined through i_photo-V curve and redox potential of quinone/hydroquinone (0.45 V). The results indicated that rose Bengal can act as donor as well as acceptor type dye The quantum efficiency of dye-sensitized photocurrent was found to be ~78%. Long-term stability experiments. Page(s): 213-219