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(418) Production(s) de l'année 2017
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Structure, thermodynamics and nature of bonding in Al3+, Cr3+, Sc3+, and Fe3+ complexes - precursors of MIL-53 metal-organic framework materials
Auteur(s): Rogacka J., Formalik F., Roszak Sz., Firlej L., Kuchta B
(Affiches/Poster)
11th Conference on Porous Solids COPS-XI (Avignon, FR), 2017-05-14
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Raman signatures of SLG dispersed in degassed water (‘‘eau de graphene’’)
Auteur(s): Bepete George, Drummond Carlos, Pénicaud Alain, Anglaret E.
Conference: NT17 (Belo Horizonte, BR, 2017-06-30)
Ref HAL: hal-01938606_v1
Exporter : BibTex | endNote
Résumé: We study the intrinsic Raman signatures of single layer graphene (SLG) dispersed in degassed water without additives, so called ‘‘eau de graphene” (EdG) and compare them to those of suspended SLG. The Raman signatures of SLG superimpose to those of water. The most characteristic signature of SLG in EdG is a narrow and symmetric 2D band with a width depending on processing conditions. The position of the G and 2D bands indicate moderate biaxial compressive strain and weak n doping. The intensity of the D band and the width of the G band are discussed in terms of point-defect density and flake size. We show that point defects can be easily cured by preparing thin films from EdG and annealing at 800°C.
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Ab initio modelling of multicomponent borosilicate glasses
Auteur(s): Ispas S.
Conférence invité: 9th International Conference on BORATE GLASSES, CRYSTALS AND MELTS (Oxford, GB, 2017-07-23)
Ref HAL: hal-01938518_v1
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Résumé: We have carried out combined classical and ab initio molecular dynamics (MD)simulations in order to investigate the structural and vibrational properties of severalborosilicate glasses. We have considered rather simple ternary compositions withvarying SiO 2 , B 2 O 3 or Na 2 O concentrations, or more complex compositionscontaining equally CaO, Al 2 O 3 or MgO. The ab initio calculations have been carriedout within the density functional theory framework as implemented in the VASPcode. The classical MD simulations were carried out using different effective pairpotentials.We have studied the local structure of the various structural units, and inparticular we have focused on the structures around the boron atoms and how theseare embedded into the network. We have investigated how the Na atoms aredistributed around the [3] B triangles and [4] B tetrahedra. Furthermore, we have foundthat the Na distribution associated to a BO 4 tetrahedron is different from thatcorresponding to a SiO 4 tetrahedron in that the former gives rise to a distribution thatis significantly more structured.The vibrational properties have been equally studied within the ab initio approach,and we have identified the contributions of the various species as well as those ofthe local structural units. We have also calculated the dielectric function ε(ω) as wellas the absorption spectra. The latter are in good quantitative agreement withexperimental data. The results obtained in this work confirm that the atomisticsimulations, in particular the ab initio ones, give access to a better understanding ofcomplex borosilicate glasses since their structural and vibrational properties can beextracted with a good accuracy and compare very well to experimental data.
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Developing empirical potentials from ab initio simulations for modelling silicate glasses
Auteur(s): Ispas S.
Conférence invité: Bridging the Scales in Glasses III (Mainz, DE, 2017-02-16)
Ref HAL: hal-01938497_v1
Exporter : BibTex | endNote
Résumé: We have parameterized empirical potentials for molecular dynamics (MD) simulations ofmulti-component silicate glasses. The main motivation has been to improve predictions ofstatic properties like elastic moduli and dynamic properties like vibrational density of states(VDOS) that MD simulations have generally not been able to estimate correctly, while stillusing a simple functional form for computational efficiency.Our approach has been to fit the potentials to data extracted from accurate first principlescalculations to predict both the static and dynamic properties correctly, by explicitly incor-porating the radial distribution function (RDF) and the VDOS into the cost function of thefitting scheme. The current optimization scheme is an extension of a recent work using asinput only the structural data from the ab initio simulations, and which has been applied inthe past to obtain a reliable potential for amorphous silica [1,2].The newly developed potentials will be used to study the elastic response of multi-componentoxide glasses to external stimuli such as high temperatures, high pressures and high strains,and their deformation modes under different loading conditions.A. Carré, J. Horbach, S. Ispas, W. Kob, Europhys. Lett. 82 (2008) 17001.A. Carré, S. Ispas, J. Horbach, W. Kob, Comput. Mater. Sci. 124 (2016) 323
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Isothermal DSC Study of the Curing Kineticsof an Epoxy/Silica Composite for Microelectronics
Auteur(s): Granado Lérys, Kempa Stefan, Bremmert Stefanie, Gregoriades Laurence, Brüning Frank, Anglaret E., Fréty Nicole
(Article) Publié:
International Journal Of Microcircuits And Electronic Packaging, vol. 14 p.45 (2017)
Ref HAL: hal-01938254_v1
DOI: 10.4071/imaps.359903
Exporter : BibTex | endNote
Résumé: Curing kinetics of an industrially important printedcircuitboard (PCB) base material (epoxy–phenol/glass fillers)were studied by isothermal differential scanning calorimetry(DSC) measurements between 150 and 190°C, as relevant curingtemperatures for the PCB industry. The extent of cure was calculatedby integration of the exothermic peak and normalizationby the total heat of reaction (obtained by nonisothermal DSC).Although the cross-linking was completed above 180°C, thekinetic profiles show two regimes: one fast and one slow. Thekinetic parameters have been elucidated using an isoconversionalmodel-free kinetic method, with the exact method of Friedman,to give to the PCB manufacturers a road map to predict curingbehavior of base material. The linearity of Arrhenius plots wassatisfactory. The apparent activation energy of curing reactionhas been found to increase with the degree of conversion. Theelucidation of the kinetic parameters allows us to propose anaccurate and predictive description of the curing kinetics withinthe fast regimen of reaction (i.e., without vitrification). Finally,we discuss how these kinetic measurements and models can becompleted and optimized.
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Modeling of low temperature adsorption of hydrogen in carbon nanopores
Auteur(s): Rogacka J., Firlej L., Kuchta B
(Article) Publié:
Journal Of Molecular Modeling, vol. 23 p.20 (2017)
Ref HAL: hal-01938159_v1
DOI: 10.1007/s00894-016-3202-y
WoS: 000394169500020
Exporter : BibTex | endNote
1 Citation
Résumé: We simulated the low temperature (T = 77 K) hydrogen adsorption in carbon slit-shaped nanopores using consecutively united atom (UA) and all atom (AA) representation of hydrogen molecule. We showed that both approximations give comparable estimation of the amount stored, for the wide range of pore width (0.6-2.5 nm). We also showed that at very high pressure (P = 400 bar, corresponding to the fugacity f used in grand canonical Monte Carlo simulations of f = 800 bar) the density of the adsorbed hydrogen structures is larger than the density of bulk liquid at critical temperature (∼76 kg/m3). This result agrees with the experimental observation of the density of the order of 100 kg/m3 for the hydrogen adsorbed in microporous carbons, reported recently in the literature.
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Core-Shell structure induces new ground states in strontium titanate
Auteur(s): Hehlen B., Kiat Jean-Michel, Al-Sabbagh A, Anoufa Mickaël, Bogicevic Christine, Al-Zein A.
Conférence invité: 12th Pacific Rim Conference on CEramics and Glass Technology (PACRIM) (Waikoloa - Hawaï, US, 2017-05-22)
Texte intégral en Openaccess :
Ref HAL: hal-01937924_v1
Exporter : BibTex | endNote
Résumé: Hyper-Raman scattering (HRS) is a non-linear spectroscopy sensitive to all polar excitations, in particular the soft modes inactive in Raman. HRS has been applied to nano-ceramics of strontium titanate (SrTiO3) of controlled grain size. Contrary to infrared absorption which sees an average medium, the vibrational responses of the core and the shell(s) are split in HRS, allowing thereby probing the structural and dielectric properties of the two subsystems. The resulting structural model successfully reproduces the effective dielectric permittivity measured by dielectric experiments [1]. These results confirm the strong, but still under-exploited, potentialities of HRS for the investigation of polar materials [2].We also demonstrate that a new ground state can be obtained by tailoring the core-shell structure of the particles. High energy X-rays at synchrotron combined to neutron diffraction and HRS revealed a lowering of the ferroelastic ground state towards a new antiferrodistortive phase, accompanied with strong shift of the critical temperature [3,4]. This new phase is discussed within the Landau theory, and the crucial competition between particle shape anisotropy, surface tension, and shear strain is analyzed as well. This shows that controlling the core-shell structure provides an easy way to stabilize new phases that cannot exist in bulk material, just like film deposition on a substrate.
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