Search results for "Hexagonal phase"
showing 10 items of 17 documents
Selenium Nanoparticles Synthesized via a Facile Hydrothermal Method
2012
Crystalline selenium nanostructures were synthesized from the reaction of a GeSe3 glass with water at 85°C for 144 hours. The hydrolysis of the Ge-Se bonds releases Se fragments in the solution where they form a colloidal suspension of amorphous nanospheres. The later evolve toward a more stable hexagonal phase (trigonal) leading to the anisotropic growth of one-dimensional monocrystalline structures. Filaments, bars and tubes of monocrystalline trigonal selenium were obtained with diameters ranging from 10 nm to 1 µm and aspect ratio up to 180. This simple process in aqueous solution opens new perspectives for the synthesis of 1D nanoparticles of trigonal selenium at large scale.
Dynamics of the labyrinthine patterns at the diffuse phase boundaries
2001
The phase diagram of a magnetic colloid in a Hele-Shaw cell is calculated. As a function of the magnetic field strength, of the concentration and of the layer thickness the magnetic colloid can find itself in a stripe phase, the hexagonal phase or in an unmodulated state. Those results allow to interpret experiments observing the transformation of a labyrinthine pattern into a hexagonal structure. This possibility is confirmed directly by the numerical simulation presented here and showing the transformation of the labyrinthine pattern into the hexagonal structure.
Fabrication of superconducting tantalum nitride thin films using infra-red pulsed laser deposition
2013
We report the successful fabrication of superconducting tantalum nitride (TaN) thin films using a pulsed laser deposition technique with 1064 nm radiation. Films with thickness $ \sim $ 100 nm deposited on MgO (100) single crystals and on oxidized silicon (SiO$_{2} $) substrates exhibited a superconducting transition temperature of $\sim $ 8 K and 6 K, respectively. The topography of these films were investigated using atomic force and scanning electron microscopy, revealing fairly large area particulate free and smooth surfaces, while the structure of the films were investigated using standard $ \theta -2 \theta $ and glancing angle X-ray diffraction techniques. For films grown on MgO a fa…
Aqueous Corrosion of the GeSe4 Chalcogenide Glass: Surface Properties and Corrosion Mechanism
2009
International audience; The aqueous corrosion behavior of the GeSe4 glass composition has been studied over time under various conditions (temperature and pH). The evolution of the surface topography by atomic force microscopy and properties such as surface hardness and reduced modulus, as well as the optical transmission in the 1-16 μm window, have been measured as a function of time spent in the corrosive solution. It was found that even if the glass reacts at room temperature, its optical transparency was barely affected. Nevertheless, the durability of GeSe4 was found to be drastically affected by an increase of both temperature and pH. Furthermore, pure selenium nanoparticles were form…
Cinnabar phase in ZnSe at high pressure
2001
We have performed an energy-dispersive x-ray-diffraction experiment on ${\mathrm{ZnSe}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ alloys under high pressure with $x=0,$ 0.05, 0.1, and 0.2. In the downstroke a hexagonal phase appears. We suggest that this phase is cinnabar, whose stability range decreases as the Te content is reduced. The analysis of the whole series of compositions enables us to establish its lattice parameters in ZnSe $(a=3.785\AA{}$ and $c=8.844\AA{}$ at 10.5 GPa). The extinction of some diffraction peaks also suggests that the internal parameters u and $v$ are close to 0.5, indicating that the cinnabar phase in ZnSe is similar to that observed in GaAs and ZnTe.
Evidence of hexagonal WO3 structure stabilization on mica substrate
2009
International audience; WO3 nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO3 hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO3 hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.
The Intrinsic Defects, Disordering, and Structural Stability of BaxSr1–xCoyFe1–yO3−δ Perovskite Solid Solutions
2012
First principles density functional theory modeling of point defects and structural disordering in BaxSr1–xCoyFe1–yO3−δ (BSCF) perovskites reveals that the material tends to decompose at low temperatures into a mixture of cubic and hexagonal perovskite and/or oxide phases. Special attention is paid to elucidating the effects of oxygen nonstoichiometry on cubic and hexagonal phase stability, decomposition energies, and oxygen vacancy formation energies. The observed lattice instability is likely to negate the advantages of the fast oxygen transport chemistry and impede the applicability of BSCF in solid oxide fuel cells and oxygen separation ceramic membranes. The general methodology present…
Synthesis of Nd:YAG nanopowder using the citrate method with microwave irradiation
2010
Abstract Nd:YAG nanopowders were prepared using the Pechini process with microwave irradiation ( MWs ). A reference sample was also prepared using conventional heating. XRD pattern analysis showed that nanopowder obtained by means of conventional heating and calcination for 1 h at 900 °C has a structure made up of the garnet phase together with the hexagonal phase that disappeared after two additional hours of thermal treatment. The MWs powder calcined for 1 h consists of the single garnet phase. SAXS data analysis indicated that nanoparticles are characterized by a sharp interface. TEM investigation showed crystalline particles with remarkable agglomeration in both samples, although a more…
Morphology and structures in double-, triple- and quadruple-chain phospholipid monolayers at the air/water interface
2007
The structure of double-, triple- and quadruple-chain phospholipid monolayers has been studied by Synchrotron x-ray diffraction. The double-chain mixed- linkage species exhibit an oblique structure at all pressures investigated. The triple-chain phospholipids show at lower lateral pressures a rectangular unit cell with a phase transition at higher pressures to a hexagonal packing of vertically arranged chains. The quadruple- chain lipid exhibits only the hexagonal phase structure. The position of the ether linkage and of the branched chain on the glycerol backbone has also a strong influence on the monolayer structures. Fluorescence microscopy shows different domain shapes for the different…
The influence of phase transitions in phosphatidylethanolamine models on the activity of violaxanthin de-epoxidase
2008
In the present study, the influence of the phospholipid phase state on the activity of the xanthophyll cycle enzyme violaxanthin de-epoxidase (VDE) was analyzed using different phosphatidylethanolamine species as model lipids. By using (31)P NMR spectroscopy, differential scanning calorimetry and temperature dependent enzyme assays, VDE activity could directly be related to the lipid structures the protein is associated with. Our results show that the gel (L beta) to liquid-crystalline (L alpha) phase transition in these single lipid component systems strongly enhances both the solubilization of the xanthophyll cycle pigment violaxanthin in the membrane and the activity of the VDE. This pha…