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

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

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 investigation of vanadium - Sodium metaphosphate glasses

cited By 10International audienceThe structure of the glass forming system (V2O5)x - (Na2O · P2C5)(1-x), (x = 0-0.4), has been investigated using Raman spectroscopy. The stretching vibrations of various phosphate groups, connected to phosphorus or vanadium atoms, have been assigned. Variation of the composition leads to structural changes where the sodium metaphosphate -P-O-P-chains break and then reconnect with the oxovanadium units forming a -V-O-P-network structure

The Reaction of Bunsen's Cacodyl Disulfide, Me2As(S)-S-AsMe2, with Iodine: Preparation and Properties of Dimethylarsinosulfenyl Iodide, Me2As-S-I

Bunsen's cacodyl disulfide, Me2As(S)-S-AsMe2 (1), reacted with iodine giving the novel dimethylarsinosulfenyl iodide, Me2As-S-I (3) although theoretical calculations indicated that the AsV compound Me2As(S)-I (4) was more stable in the gas phase. The oily product was stable neat and as a solution in CDCl3 at +4 °C and -20 °C for at least 15 d. Light, H2O, H2O2, and Zn dust, but not NaI or Ag, decomposed it. Compound 3 did not interact with Ph3N, with Ph2NH and PhNH2 it interacted but not reacted. 3 was decomposed by piperidine, with pyridine and 4-dimethylaminopyridine it interacted and produced Me2As-SS-AsMe2 (2) and I2 that formed charge transfer complexes Base·I2, whereas Et3N decomposed 3, and 3Et3N·2I2 was isolated. 3 was desulfurized by Ph3P and (Me2N)3P completely, and by (PhO)3P and (PhS)3P partially. The reactions of 3 with (Me2N)3P, (PhS)3P, and (EtO)3P were complicated. From the AsIII nucleophiles, only Ph3As was bound, while (PhS)3As reacted slowly in a complicated manner with 3. No interaction of 3 with MeOH or PhOH was observed but NaOH, Ag2O, and PhONa decomposed it. Thiophenol produced traces of Me2As-SPh (10) and sodium thiophenolate attacked mainly at AsIII of 3. Thus, externally stabilized sulfenium ions of the type Me2As-S-Nu+I- were not obtained. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim