0000000001068650

AUTHOR

N. Floquet

Heptane adsorption in silicalite-1 : molecular dynamics simulation.

Molecular dynamics (MD) simulations have been used to study the adsorption process of n-heptane molecules in silicalite-1 at 300 K. MD simulated results were compared to experimental neutron diffraction (ND) and experimental self-diffusion coefficients. The analysis of MD data indicated a packing of the adsorbed molecules around 4 mol./u.c., which is not the consequence of an enthalpic effect but of an entropic effect. The role of the n-heptane chain flexibility (cis–trans conformation) in relation with the silicalite-1 channel type (straight versus sinusoidal) was outlined and enabled to understand the mobility change arising at 4 mol./u.c., according to previous experimental results. The …

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Interaction of oxygen with Mo(100), Mo(110), and Mo(111) surfaces. RHEED and AES analyses of the molybdenum oxide nucleation and growth

Abstract A study of the nucleation and growth of MoO 3 generated by interaction of oxygen with Mo(100), Mo(110), and Mo(111) single crystalline surfaces is investigated at high oxygen pressure (10 4 Pa) and low temperature (620 to 820 K). The results of RHEED and AES analyses prove that under these oxidation conditions, MoO 3 nucleates directly from the metal without intermediate formation of MoO 2 or nonstoichiometric molybdenum oxide such as Mo 4 O 11 . The structure and orientation of MoO 3 nuclei are characterized in relation with the parent molybdenum surface. On the Mo(110) and Mo(111) surfaces, which are faceting, the nucleation and growth of MoO 3 takes place by successive structura…

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Fine grain barium titanate: ferroelectric domains and X-ray diffraction diagram

Through three different studies using various kinds of BaTiO/sub 3/ samples: as a powder while heating over the Curie temperature; as a green ceramic as a function of the forming pressure; as a ceramic while applying a D.C. field. It is shown how X-ray diffraction is able to give information about the evolution of the 90/spl deg/ ferroelectric domain microstructure.

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Superficial oxidation of molybdenum at high pressure and low temperature: RHEED and AES analyses of the molybdenum oxide formation

Abstract Numerous studies relate to the interaction of the molybdenum surface with oxygen at low pressure and high temperature. They give results about oxygen chemisorption, surface facetting and the epitaxial formation of MoO 2 crystallites. This work deals with the interaction of Mo(100), Mo(110) and Mo(111) surfaces with oxygen at high pressure (10 4 Pa) and low temperature (620–820 K). RHEED and AES analyses results prove that, in these oxidation conditions: MoO 2 and non-stoichiometric molybdenum oxide such as Mo 4 O 11 are not evidenced in any of the molybdenum oxidation steps. The MoO 3 phase nucleates directly from any Mo surface. The structure and orientation of MoO 3 nuclei are ch…

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Microstructure of 90° Domains in Ferroelectric Materials studied by XRD

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Ferroelectric domains in BaTiO3powders and ceramics evidenced by X-ray diffraction

Abstract Through three different studies, using BaTiO3 samples, as a powder while heating over the Curie temperature, and as a ceramic while applying an electric field, it is shown how X-ray diffraction (XRD) is able to give information about the evolution of the ferroelectric domain microstructure. Firstly, the relative intensities of the 002 and 200 lines, as a function of the applied electric field, exhibit the motion of the 90[ddot] domain walls. However, XRD is unable to provide any distinction between two 180[ddot] domains. Secondly, the profile of those two lines and of the other double (hhl), (lhh) lines is particular: the unusual diffracted intensity between such double lines has t…

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Structural Signatures of Type IV Isotherm Steps:  Sorption of Trichloroethene, Tetrachloroethene, and Benzene in Silicalite-I

We have investigated by in situ neutron diffraction the structural properties of C2HCl3, C2Cl4, and C6D6 sorbed phases in silicalite-1. Our motivation is to correlate the structure of these three confined species to the fact that their adsorption isotherms are characterized by no step, one step, and two steps, respectively. From our detailed neutron diffraction investigation, we deduce that the adsorption isotherm steps are not signatures of phase transitions but are correlated to the different adsorption stages observed during the silicalite-1 loading. For C6D6, such a loading is a three stage process (the C6D6 molecules fill successively, the intersections, then the straight channels and …

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A New Possibility for Powder Diffraction: The Characterization of the Domain Microstructure in a Ferroelectric Material

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Inelastic neutron scattering study of proton dynamics in Ca(OH)2 at 20 K

Abstract Inelastic neutron scattering (INS) spectra of Ca(OH) 2 at 20 K are presented from 30 to 4000 cm −1 for a powder sample, from 30 to 12000 cm −1 for an oriented single-crystal. INS band splitting due to the lattice density-of-states is observed. Polarization effects reveal the orientation of atomic displacements for each mode and a new band assignment scheme is proposed. For the single-crystal, the v OH mode and overtones are observed. This oscillator shows only moderate anharmonicity. Spectrum simulation reveals that INS spectral intensities are not consistent with simple normal coordinates and harmonic force-fields for Ca(OH) 2 entities. A new dynamical model is proposed, including…

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Ferroelectric Domain Walls in BaTiO3: Fingerprints in XRPD Diagrams and Quantitative HRTEM Image Analysis

The structure of ferroelectric domain walls in BaTiO3 has been investigated through two complementary approaches, a global one by the fine analysis of X-ray diffraction patterns, the other essentially local via a quantitative image analysis method developed and applied to High Resolution Transmission Electron Microscopy images. These two original approaches converge towards a clear description of 90○ walls which are shown to be a 4–6 nm wide region where the crystallographic discontinuity is accommodated by irregular atomic displacements. The results given here demonstrate that the usual structural theoretical description of walls commonly accepted for energy calculations are far too simpli…

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Heptane Adsorption in Silicalite-I : Neutron Scattering Investigation.

International audience

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Heptane Adsorption in Silicalite-1: Neutron Scattering Investigation

International audience; Structural properties of confined deuterated n-heptane in silicalite-1 have been investigated by neutron scattering experiments during the adsorption process. At 300 K, the adsorption isotherm shows a sharp inflection at a loading near Nads ) 4 molecules per silicalite-1 unit cell. In addition, the diffusivities obtained from recent QENS data exhibit a loading dependence. Our motivation is to find structural signatures of the peculiar behavior of n-heptane in silicalite-1 and to check the numerous computer simulation findings of this behavior. Our detailed neutron diffraction investigation agrees with the MONO-ORTHO phase transition of the silicalite-1 above a Nads v…

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