Glass structure and ion dynamics of lead-cadmium fluorgermanate glasses

Glass structure and fluorine motion dynamics are investigated in lead-cadmium fluorgermanate glasses by means of differential scanning calorimetry, Raman scattering, x-ray absorption (EXAFS), electrical conductivity (EC), and F-19 nuclear magnetic resonance (NMR) techniques. Glasses with composition 60PbGeO(3)-xPbF(2)-yCdF(2) (in mol %), with x+y=40 and x=10, 20, 30, 40, are studied. Addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (T-g) and to an enhancement of the ionic conductivity properties. Raman and EXAFS data analysis suggest that metagermanate chains form the basic structural feature of these glasses. The NMR study leads to the conclusion that the F-F distances are similar to those found in pure crystalline phases. Experimental results suggest the existence of a heterogeneous glass structure at the molecular scale, which can be described by fluorine rich regions permeating the metagermanate chains. The temperature dependence of the NMR line shapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluorine mobility in these systems. (C) 2004 American Institute of Physics.

Theoretical and experimental study of the relation between photoluminescence and structural disorder in barium and strontium titanate thin films

Thin films of barium and strontium titanate (BST), synthesized by the polymeric precursor solution and spin coated on [Pt (140nm)/Ti (10 nM)/SiO2(1000 nm)/Si] substrates were found to be photoluminescent at room temperature when heat treated below 973 K, i.e. before their crystallization. First principles quantum mechanical techniques, based on density functional theory (DFT) were employed to study the electronic structure of two periodic models: one is standing for the crystalline BST thin film and the other one for the structurally disordered thin film. The aim is to compare the photoluminescence (PL) spectra of the crystalline and disordered thin films with their UV-vis spectra and with their computed electronic structures. The calculations show that new localized states are created inside the band gap of the crystalline model, as predicted by the UV-vis spectra. The study of the charge repartition in the structure before and after deformation of the periodic model shows that a charge gradient appears among the titanate clusters. This charge gradient, together with the new localized levels, gives favorable conditions for the trapping of holes and electrons in the structure, and thus to a radiative recombination process. Our models are not only consistent with the experimental data, they also allow to explain the relations between structural disorder and photoluminescence at room temperature. (c) 2005 Elsevier Ltd. All rights reserved.

Morphology characterization of layer-by-layer films from PAH/MA-co-DR13: the role of film thickness

We report on the use of dynamic scale theory and fractal analyses in the Study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed oil glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The ganular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains. The growth outside the grains was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of ca. 2.6. One could expect that inside the grains the morphology would be close to a Euclidian surface with fractal dimension of ca. 2 for any growth stage. The latter, however, was observed only for thicker films containing more than 10 bilayers. For thinner films the morphology was well described by a self-affine fractal. Such dependence of the growth behavior with the film thickness is associated with a more complete coverage of adsorption sites in thicker films due to diffusion of polymer molecules. (c) 2004 Elsevier B.V. All rights reserved.

Barium strontium titanate nanocrystalline thin films prepared by soft chemical method

Barium strontium titanate (Ba0.65Sr0.35TiO3) nanocrystalline thin films, which were produced by the soft chemical method, were crystallized at low temperature using a domestic microwave oven. A SiC susceptor were used to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are crack-free, well-adhered, and fully crystallized. The microstructure displayed a polycrystalline nature with nanograin size. The metal-BST-metal structure of the thin films treated at 700 degrees C show food electric properties. The ferroelectric nature of the BST35 thin film was indicated by buttertly- shaped C-V curves. The capacitance-frequency curves reveal that the dielectric constant may reach a value up to 800 at 100kHz. The dissipation factor was 0.01 at 100kHz. The charge storage density as function of applied voltage graph showed that the charge storage densities are suitable for use in trench type 64 Mb ( 1-5 mu C/cm(2) and 265 Mb (2-11 mu C/cm(2)) DRAMs. (C) 2007 Elsevier Ltd. All rights reserved.

Crystal and molecular structures of 4-substituted 3,4-dihydropyrimidin-2(1H)-ones studied by X-ray and AM1 and B3LYP calculations

(1) C13H13N3O5, Mr = 291.26, P (1) over bar, a = 7.4629(9), b = 7.9203(9), c = 12.126(2) angstrom, alpha = 86.804(5), beta = 78.471(7), gamma = 69.401(8)degrees, V = 657.3(2)angstrom(3), Z = 2, R-1 = 0.0454; (2) C11H12N2O4, Mr=236.23, Pbca, a=7.2713(9), b=14.234(1), c=20.848(3)angstrom, V= 2157.8(4) angstrom(3), Z=8, R-1=0.0504; (3) C13H13N2O3Cl, Mr = 280.70, P2/n, a = 17.344(2), b = 9.237(1), c = 18.398(2) angstrom; beta = 92.61(2)degrees, V = 2944.4(6) angstrom(3), Z = 8, R-1 = 0.0714. The conformational features of three 4-substituted-3-4-dihydropyrimidin-2(1H)-ones were investigated by computational and single crystal X-ray crystallographic studies. The geometries were optimized using semiempirical (AM1) and first principle calculations (B3LYP/6-31G**) methods, the rotational barriers for important functional groups were studied. In all structures the pyrimidinone rings are in a more or less distorted boat conformation. The phenyl and the furane rings are almost perpendicular to the best least-squares plane through the dihydropyrimidinone ring.

Application of standard and modified Judd-Ofelt theories to thulium doped fluoroindate glass

Fluoroindate glasses of the following compositions: (40-x)InF3-20ZnF(2)-16BaF(2)-20SrF(2)-2GdF(3)-2NaF-xTmF(3) with x = 1,3 mol% were prepared in a dry box under an argon atmosphere. The absorption spectra at room temperature in the spectral range 350-2200 nm were obtained. The spectra obtained for each sample had similar absorption and only the amplitude of the different bands changed as the concentration of Tm3+. The experimental oscillator strengths were determined from the areas under the absorption bands. Using the standard and modified Judd-Ofelt theory, intensity parameters Ohm(lambda) (lambda = 2,4,6) and (lambda = 2,3,4,5,6), respectively for f-f transitions of Tm3+ ions as well as transition probabilities, branching ratios and radiative lifetimes for each band were determined. The results are compared with those of other glasses described in the literature. (C) 1999 Elsevier B.V. B.V. All rights reserved.

BIOACTIVE AND OTHER PIPERIDINE ALKALOIDS FROM CASSIA-LEPTOPHYLLA

Four new piperidine alkaloids, leptophyllin A (4), 3-acetylleptophyllin A (5), leptophyllin B (8), and (-)-spectaline (1), and 3 known piperidine alkaloids, (-)-spectalinine (2), canavaline (3), and iso-6-canavaline (7), were isolated by a bioassay-guided fractionation of a leaf extract of Cassia leptophylla. The alkaloids 1 - 3 were active in a mechanism-based DNA-modifying yeast assay and 2 was moderately active in Vero monkey and Chinese hamster ovary cell cytotoxicity assays.

Physicochemical parameters involved in the lethal toxicity of N,N-[(dimethylamino)ethyl]-4-substituted benzoate hydrochlorides: A QSAR study

A set of sixteen para-substituted N,N-[(dimethylamino)ethyl] benzoate hydrochlorides structurally related to procaine was synthesized. The apparent partition coefficients were determined by either shake-flask or HPLC methods and were taken as hydrophobic parameters. The IR stretching frequencies of the carbonyl group were determined in chloroform and taken as one of the electronic parameters. Additional physicochemical parameters were either taken from the literature: pi, sigma, T and R, MR4, or calculated: log P. The lethal potency was determined in the mouse via the LD50. In order to verify the nature and the relative contributions of the physicochemical parameters to lethal toxicity, QSAR equations were derived using regression analysis. A major contribution of hydrophobicity to ether with a smaller but still significant contribution of electronic or polar properties was found to a describe the toxicity within this set of compounds.

SiO2-PbF2-CdF2 glasses and glass ceramics

Lead-Cadmium fluorosilicate stable glasses were prepared and the vitreous domain region determined in the composition diagram. Characteristic temperatures were obtained from thermal analysis and the structural studies performed illustrate clearly the role played by lead atoms in the glasses crystallization behavior and the glass-forming ability of cadmium atoms. The occurrence of either a cubic lead fluoride or a lead-cadmium fluoride solid solution in crystallizing samples was found to be dependent on Er3+ doping. The optically active ions were found to concentrate in the crystalline phase and in fact play the role of nucleating agent as suggested from X-ray diffraction and EXAFS measurements. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Strontium titanate films prepared by spray pyrolysis

Strontium titanate thin films were prepared by spray pyrolysis technique. Deposition parameters, such as solution concentration, time and temperature of deposition, and flow rate of carrier gas were optimized to obtain dense films without cracks. Films with different thicknesses were prepared through the control of deposition time. Prepared thin films were homogeneous, well crystallized, with uniform grain size. (C) 2003 Elsevier Ltd. All rights reserved.

An ultra stable glass system for optical fiber devices

In this paper a modified chalcogenide glass was studied by X-ray powder diffraction, differential thermal analysis, infrared and Raman scattering spectroscopies. The study of this new matrix opens new perspectives to fabricate Pr3+-doped fibers to operate as an optical amplifier in the 1.3 mum telecommunications window. The Pr3+-doped 70Ga(2)S(3)-30La(2)S(3) glass was modified through the substitution of La2S3 by La2O3, which improves the thermal stability of these glasses without any modification of phonon energy. The possibility to pull a fiber from this glass system without any devitrification is easily achieved.