93 research outputs found
Complex dynamics in nanoscale phase separated supercooled liquids
The relaxation properties of supercooled AsxS100−x liquids are investigated using a combination of infrared
photon correlation spectroscopy and topological constraint theory. Results reveal two channels of relaxation
for sulfur-rich compositions that manifest by an unusual profile in the density-density autocorrelation function
involving two typical timescales. This indicates a reduced temperature-dependent dynamics for one of the
channels associated with a sulfur-rich segregated nanoscale phase that furthermore displays a low liquid fragility.
Conversely, the dynamics of the emerging cross-linked As-S network is associated with a growth of the
glass transition temperature with As content. These results can be quantitatively understood from topological
constraint theory applied to a phase separated network for which a dedicated constraint enumeration must be
achieved. The vanishing of this peculiar behavior occurs close to the reported isostatic reversibility window
observed at the glass transition
Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films
Amorphous chalcogenide thin film deposition can be achieved by a spin-coating
technique from proper solutions of the corresponding glass. Films produced in
this way exhibit certain grain texture, which is presumably related to the
cluster size in solution. This paper deals with the search of such a
correlation between grain size of surface morphology of as-deposited
spin-coated As33S67 chalcogenide thin films and cluster size of the glass in
butylamine solutions. Optical absorption spectroscopy and dynamic light
scattering were employed to study optical properties and cluster size
distributions in the solutions at various glass concentrations. Atomic force
microscopy is used to study the surface morphology of the surface of
as-deposited and thermally stabilized spin-coated films. Dynamic light
scattering revealed a concentration dependence of cluster size in solution.
Spectral-dependence dynamic light scattering studies showed an interesting
athermal photo-aggregation effect in the liquid state.Comment: 15 pages, 8 figure
Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide
The hydrothermal carbonation of calcium hydroxide (Ca(OH)2) at high pressure
of CO2 (initial PCO2 1/4 55 bar) and moderate to high temperature (30 and 90
1C) was used to synthesize fine particles of calcite. This method allows a high
carbonation efficiency (about 95% of Ca(OH)2-CaCO3 conversion), a significant
production rate (48 kg/m3 h) and high purity of product (about 96%). However,
the various initial physicochemical conditions have a strong influence on the
crystal size and surface area of the synthesized calcite crystals. The present
study is focused on the estimation of the textural properties of synthesized
calcite (morphology, specific surface area, average particle size, particle
size distribution and particle size evolution with reaction time), using
Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller
(BET) measurements, and scanning electron microscope (SEM) and transmission
electron microscope (TEM) observations. This study demonstrate that the
pressure, the temperature and the dissolved quantity of CO2 have a significant
effect on the average particle size, specific surface area, initial rate of
precipitation, and on the morphology of calcium carbonate crystals. In
contrast, these PTx conditions used herein have an insignificant effect on the
carbonation efficiency of Ca(OH)2. Finally, the results presented here
demonstrate that nano-calcite crystals with high specific surface area (SBET
1/4 6-10m2/g) can be produced, with a high potential for industrial
applications such as adsorbents and/or filler in papermaking industry
UV photo-detector based on p-NiO thin film/n-ZnO nanorods heterojunction prepared by a simple process
Zno nanowires: Growth, properties and advantages
One-dimensional anisotropic nanostructures, and in particular nanowires, are under intensive investigations over the last decade owing to their unique physical properties and their documented performance in a wide range of opto-electronic and nano-photonic devices. Here, we present a short overview of the main assets of nanowire arrays with particular emphasis as materials for solar energy harvesting and conversion. A brief survey on the main growth techniques of ZnO nanowires, i.e. chemical vapor deposition and solution chemistry is also presented. © Springer Science+Business Media Dordrecht 2015
A density functional investigation of the structural and vibrational properties of the highly symmetric molecules M4O6, M4O10 (M = P, As, Sb, Bi)
cited By 5International audienceThe group 15 (VA) M4O6, M4O10 (M: N, P, As, Sb, Bi) oxides have a cage-like structure. These compounds could be found as isolated gas-phase molecules or as structural units in condensed systems. They serve as molecular 'models' that could describe the structure and physicochemical properties of various solid- and liquid-state systems. The knowledge of the geometric parameters (bond lengths, angles), of the atomic charges and of the bond stretching frequencies is important for the investigation and understanding of the nature of the metal-oxygen chemical bonds in these molecules. In the present work we systematically investigated by density function theoretical (DFT) methods the modification of the structure and of the vibrational spectrum of the M4O6 and M4O10 molecules at two different symmetries (Td and D2h). Computer calculations were performed at the B3LYP level of theory using the LanL2DZ (ECP) basis set. An enlargement of the metal-oxygen bond length and a shift of vibrations to lower frequencies have been observed when the metal element changes from phosphorous to bismuth, for both oxidation states and symmetries. © 2008 Elsevier B.V. All rights reserved
PHYSICOCHEMICAL INVESTIGATION OF THE VANALIOUM COMPLEXES FORMED IN MOLTEN ALKALI-PYROSULFATE AND ALKALI-SULFATE USING RAMAN AND UV/VIS SPECTROSCOPY
Computational study of structural, vibrational and electronic properties of the highly symmetric molecules M4S6 (M = P, As, Sb, Bi)
A systematic computational investigation of the structural, electronic and vibrational properties of the group 15 sulfides M4S6 at Td symmetry was carried out. The performance of DFT and MP2 theoretical methods was assessed compared to the high-level CCSD method. The M–S bond is based on the association between p valence orbitals of M and the 3p of sulfur according to the natural population analysis. Both polarizability and polarizability volume of the cage molecules increase as the size of the atoms increases from P to Bi. A structural ‘relaxation’ ongoing from phosphorus to bismuth showed an increase of ionic character and it might explain the chemical instability of the heavier cage compounds. For the P4S6 molecule, the functionals wB97XD and CAMB3LYP yielded excellent structural data, while for the heavier molecules As4S6, Sb4S6 and Bi4S6, the M06 and M06L functionals showed high accuracy. We validated eight functionals BP86, M06L, B3LYP, M06, Μ06-2Χ CAMB3LYP, wB97XD, B2PLYP which span from conventional GGA functionals to long-range corrected hybrid ones, and MP2, CCSD ab initio methods. Experimentally, these molecules could be useful in the structural investigation of the isolated gas phase species, besides solving complex structures of liquid, crystalline or amorphous phases. © 2019 Elsevier B.V
Structural and Redox Properties of Vanadium Complexes in Molten Salts of Interest for the Catalytic Oxidation of Sulfur Dioxide
Structural and Redox Properties of Vanadium Complexes in Molten Salts of Interest for the Catalytic Oxidation of Sulfur Dioxide
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