XRD Studies (xrd + studies)

Distribution by Scientific Domains

Selected Abstracts

Growth of YCOB single crystals by flux technique and their characterization

R. Arun Kumar
Abstract Nonlinear optical single crystals of YCOB with good optical quality were grown by the flux technique for the first time. Polycrystalline YCOB samples were synthesized by solid state reaction method. The thermal analysis of the sample was performed with lithium carbonate flux in different weight proportions and the growth temperature was optimised. Single crystals of YCOB with dimensions 3 3 5 mm3 were obtained by the method of ,slow-cooling'. The grown crystals were characterized by XRD, UV-VIS-NIR, EDAX, FTIR and etching studies. The powder XRD pattern revealed the formation of YCOB compound. The lattice parameters were identified through single crystal XRD studies. The UV-VIS-NIR results showed that the crystal has a sharp cutoff at 220 nm and is nearly 55% transparent over a wide wavelength range enabling applications in the UV region. The EDAX measurement revealed the ,flux-free' crystal formation. The presence of the functional groups belonging to the YCOB crystals was identified by the FTIR results. ,Hillock-like' patterns are observed in the etching studies. The primary emphasis in this study is laid to describe ,flux technique' as an alternative method to grow YCOB crystals. The results are presented and discussed. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Studies on electrical conduction behavior of La1-3xCaxBaxSrxMnO3 synthesized by chemical route

K. D. Mandal
Abstract In the manganite La1-xMxMnO3 (M = Ca, Ba, Sr) the doping concentration introduces a mixed valency (Mn3+, Mn4+) which governs the magnetic and electrical properties of the compound. The perovskite oxides La1-3xCaxBaxSrxMnO3 (x = 0.00, 0.05, 0.10) were prepared by chemical method. Single-phase formation is confirmed by XRD studies. The electrical behavior of compositions with x = 0.00, 0.05 and 0.10 in the system La1-3xCaxBaxSrxMnO3 was studied in the temperature range 300-420 K. It is observed that conductivity decreases with increasing temperature as well as dopants concentration. Metallic behavior of these compositions decreases with increasing dopants concentration (x). The microstructures of these samples have been characterized using scanning electron microscopy (SEM). ( 2007 WILEY -VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Preparation and characterization of ZnO nanofibers by electrospinning

R. Siddheswaran
Abstract Electrospun ZnO nanofibers were obtained by calcinating PVA/Zinc Acetate composite fibers at various temperatures. Atomic Force Microscopy (AFM) revealed that the ZnO fibers have diameters in the range of 100-200 nm. The fibers were characterized by FT- IR, TGA-DTA, and XRD studies. The XRD results showed that the crystal structure and the morphology of the fibers were largely dependent on the calcination temperature ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,

H.-L. Cheng
Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source]

Dissolution of artemisinin/polymer composite nanoparticles fabricated by evaporative precipitation of nanosuspension

Mitali Kakran
Abstract Objectives An evaporative precipitation of nanosuspension (EPN) method was used to fabricate composite particles of a poorly water-soluble antimalarial drug, artemisinin, with a hydrophilic polymer, polyethylene glycol (PEG), with the aim of enhancing the dissolution rate of artemisinin. We investigated the effect of polymer concentration on the physical, morphological and dissolution properties of the EPN-prepared artemisinin/PEG composites. Methods The original artemisinin powder, EPN-prepared artemisinin nanoparticles and artemisinin/PEG composites were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), dissolution testing and HPLC. The percentage dissolution efficiency, relative dissolution, time to 75% dissolution and mean dissolution time were calculated. The experimental drug dissolution data were fitted to various mathematical models (Weibull, first-order, Korsemeyer,Peppas, Hixson,Crowell cube root and Higuchi models) in order to analyse the release mechanism. Key findings The DSC and XRD studies suggest that the crystallinity of the EPN-prepared artemisinin decreased with increasing polymer concentration. The phase-solubility studies revealed an AL -type curve, indicating a linear increase in drug solubility with PEG concentration. The dissolution rate of the EPN-prepared artemisinin and artemisinin/PEG composites increased markedly compared with the original artemisinin powder. Conclusions EPN can be used to prepare artemisinin nanoparticles and artemisinin/PEG composite particles that have a significantly enhanced dissolution rate. The mechanism of drug release involved diffusion and erosion. [source]

XRD studies, vibrational spectra, and molecular structure of 1H-imidazo [4,5-b]pyridine based on DFT quantum chemical calculations

L. Dymi
Abstract The molecular structures and vibrational properties of 1H -imidazo[4,5-b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X-ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee,Yang,Parr correlation functional (B3LYP) and 6-31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna21(C2v9) and Z = 4. The planar conformation of the skeleton and presence of the NHN hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4,294 K and 8,295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright 2009 John Wiley & Sons, Ltd. [source]

Synthesis and Characterization of Mixed-Metal Oxide Nanopowders Along the CoOx,Al2O3 Tie Line Using Liquid-Feed Flame Spray Pyrolysis

Jose Azurdia
We report here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce a series of nanopowders along the CoOx,Al2O3 tie line. The process is a general aerosol combustion synthesis route to a wide range of lightly agglomerated oxide nanopowders. The materials reported here were produced by aerosolizing ethanol solutions of alumatrane [Al(OCH2CH2)3N] and a cobalt precursor, made by reacting Co(NO3)26H2O crystals with propionic acid. The compositions of the as-produced nanopowders were controlled by selecting the appropriate ratios of the precursors. Nine samples with compositions (CoO)y(Al2O3)1,y, y=0,1 along the CoOx,Al2O3 tie line were prepared and studied. The resulting nanopowders were characterized by X-ray fluorescence, BET, scanning electron microscopy, high-resolution transmission electron micrographs, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and FTIR. The powders typically consist of single-crystal particles <40 nm diameter and specific surface areas (SSAs) of 20,60 m2/g. XRD studies show a gradual change in powder patterns from ,-Al2O3 to Co3O4. The cobalt aluminate spinel phase is observed at stoichiometries (21 and 37 mol%) not seen in published phase diagrams, likely because LF-FSP processing involves a quench of >1000C in microseconds frequently leading to kinetic rather than thermodynamic products. Likewise, the appearance of Co3O4 rather than CoO as the end member in the tie line is thought to be a consequence of the process conditions. TGA studies combined with diffuse reflectance FTIR spectroscopic studies indicate that both physi- and chemi-sorbed H2O are the principal surface species present in the as-processed nanopowders. The only sample that differs is Co3O4, which has some carbonate species present that are detected and confirmed by a sharp mass loss event at ,250C. The thermal behavior of the high cobalt content samples differs greatly from the low cobalt content samples. The latter behave like most LF-FSP-derived nanopowders exhibiting typical 1%,4% mass losses over the 1400C range due mostly to loss of water and some CO2. The high cobalt content samples exhibit a sharp mass loss event that can be attributed to the decomposition of Co3O4 to CoO. [source]

Behavior of Silver and Palladium Mixtures during Heating

Terry Garino
The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X-ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high-temperature XRD studies on a commercial 20% palladium material with submicrometer-sized particles indicated that an intermetallic phase, most likely Ag3Pd, formed in air between 300 and 400C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525C. No PdO was detected by XRD at 400C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375C. When the material was heated in argon for 1 h at 400C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5,30 ,m) with palladium particles (1,3 ,m) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium. [source]

A comparative study on camphorsulphonic acid modified montmorillonite clay based conducting polymer nanocomposites

Ufana Riaz
Nanotechnology has emerged as a subject of immense academic interest and excitement in the past few decades. The immediate goal of this science aims at the production of high performance nanomaterials. The present study reports comparative investigations on the in situ polymerization of polyaniline (PANI), and its derivatives poly(1-naphthylamine) (PNA) and poly(o -toluidine) (POT) within the camphor sulphonic acid (CSA) modified montmorillonite (MMT) layers. The polymerization as well as intercalation of the conducting polymers was confirmed by FT-IR, UV-visible spectroscopies, and XRD studies, whereas the morphology of the nanocomposites was analyzed by TEM studies. It was found that the PANI derivatives (PNA and POT) revealed higher intercalation as compared with PANI. The morphology of nanocomposites was found to be governed by the type of conducting polymer intercalated. A large variation in the morphology as well as particle size was observed between the nanocomposites of PANI and its derivatives. The conductivity was found to be in the range of 10,3,10,2 Scm,1. POLYM. COMPOS., 2010. 2009 Society of Plastics Engineers [source]

Deposition of copper-doped iron sulfide (CuxFe1,xS) thin films using aerosol-assisted chemical vapor deposition technique

Sujit D. Disale
Abstract Copper-doped iron sulfide (CuxFe1,xS, x = 0.010,0.180) thin films were deposited using a single-source precursor, Cu(LH)2Cl2 (LH = monoacetylferrocene thiosemicarbazone), by aerosol-assisted chemical vapor deposition technique. The Cu-doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 C. The deposited thin films were characterized by X-ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X-ray analysis (EDX) and atomic force microscopy. XRD studies of Cu-doped FeS thin films at all the temperatures revealed formation of single-phase FeS structure. With increasing substrate temperature from 250 to 450 C, there was change in morphology from wafer-like to cylindrical plate-like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 C. Raman data supports the doping of copper in FeS films. Copyright 2010 John Wiley & Sons, Ltd. [source]

Direct Oxidation of Benzene to Phenol by Dioxygen over Nano-vanadium Oxide

Xiaohan Gao
Abstract Reducing regents, such as ascorbic acid, are needed for vanadium-containing catalysts to catalyze the direct oxidation of benzene to phenol by dioxygen. Quadrivalent vanadium species, reduced from quinquevalent vanadium species, can activate dioxygen to produce active oxygen species, which is important for the reaction. The key step is to prepare more V4+ -containing catalysts. Here, VOX -C16 -A was prepared in an acidic medium to produce more V4+ species. The results of XPS and XRD studies confirmed that the vanadium species in VOX -C16 -A was mainly V4+ ions. The results of XRD and electron diffraction patterns revealed that VOX -C16 -A consisted of tetragonal VO2 and monoclinic VO2. Morphology observations display that the VOX -C16 -A is made of nanorod. Investigations into the performances of the catalysts showed that VOX -C16 -A was reusable, producing a 1.9% conversion of benzene without reducing agent. [source]

Chiral ureas with two electronegative substituents at 1-N: An unusual case of coexisting pyramidal and almost planar 1-N atoms in the same crystal,

CHIRALITY, Issue 7 2009
Oleg V. Shishkin
Abstract XRD studies of structure of N -acetoxy- N -methoxyurea and N,N -bis(methoxycarbonyl)- N -methoxyimide have revealed that in N -methoxy- N -X-ureas (X = OAc, Cl, OMe, N+C5H5) the additional shortening of NOMe bond took place, which arising from an nO(Me) -,*NX anomeric orbital interaction. XRD studies of N -chloro- N -ethoxyurea crystal have revealed the presence of two kinds of anomeric nitrogen configuration in the ONCl group in the form of a pyramidal configuration and a planar configuration for same 1-N nitrogen atom. XRD studies of N -4-chlorobenzoyloxy- N -ethoxyurea have revealed that the degree of pyramidality of the 1-N nitrogen in N -aroyloxy- N -alkoxyureas is tuned by orientation of benzoyl group with respect to the NO bond, which in turn depends of size of N -alkoxy group. Chirality, 2009. 2008 Wiley-Liss, Inc. [source]