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Renaudin G.,National Graduate School of Chemistry of Clermont Ferrand | Renaudin G.,CNRS Laboratory of Inorganic Materials | Filinchuk Y.,European Synchrotron Radiation Facility | Neubauer J.,Friedrich - Alexander - University, Erlangen - Nuremberg | Goetz-Neunhoeffer F.,Friedrich - Alexander - University, Erlangen - Nuremberg
Cement and Concrete Research | Year: 2010

Two different techniques were used to compare structural characteristics of "wet" ettringite (stored in the synthesis mother liquid) and "dried" ettringite (dried to 35% relative humidity over saturated CaCl2 solution). Lattice parameters and the water content in the channel region of the structure (site occupancy factor of the water molecule not bonded to cations) as well as microstructure parameters (size and strain) were determined from a Rietveld refinement on synchrotron powder diffraction data. Local environment of sulphate anions and of the hydrogen bonding network was characterized by Raman spectroscopy. Both techniques led to the same conclusion: the "wet" ettringite sample immersed in the mother solution from the synthesis presents similar structural features as ettringite dried to 35% relative humidity. An increase of the a lattice parameter combined with a decrease of the c lattice parameter occurs on drying. The amount of structural water, the point symmetry of sulphate and the hydrogen bond network are unchanged when passing from the wet to the dried ettringite powder. Ettringite does not form a high-hydrate polymorph in equilibrium with alkaline solution, in contrast to the AFm phases that lose water molecules on drying. According to these results we conclude that ettringite precipitated in aqueous solution at the early hydration stages is of the same chemical composition as ettringite present in the hardening concrete. © 2009 Elsevier Ltd. All rights reserved.

Eychenne J.,CNRS Magmas and Volcanoes Laboratory | Le Pennec J.-L.,CNRS Magmas and Volcanoes Laboratory | Troncoso L.,National Polytechnic School of Ecuador | Gouhier M.,CNRS Magmas and Volcanoes Laboratory | And 2 more authors.
Bulletin of Volcanology | Year: 2012

The violent August 16-17, 2006 Tungurahua eruption in Ecuador witnessed the emplacement of numerous scoria flows and the deposition of a widespread tephra layer west of the volcano. We assess the size of the eruption by determining a bulk tephra volume in the range 42-57 × 10 6 m 3, which supports a Volcanic Explosivity Index 3 event, consistent with calculated column height of 16-18 km above the vent and making it the strongest eruptive phase since the volcano's magmatic reactivation in 1999. Isopachs west of the volcano are sub-bilobate in shape, while sieve and laser diffraction grain-size analyses of tephra samples reveal strongly bimodal distributions. Based on a new grain-size deconvolution algorithm and extended sampling area, we propose here a mechanism to account for the bimodal grain-size distribution. The deconvolution procedure allows us to identify two particle subpopulations in the deposit with distinct characteristics that indicate dissimilar transport-depositional processes. The log-normal coarse-grained subpopulation is typical of particles transported downwind by the main volcanic plume. The positively skewed, fine-grained subpopulation in the tephra fall layer shares close similarities with the elutriated co-pyroclastic flow ash cloud layers preserved on top of the scoria flow deposits. The area with the higher fine particle content in the tephra layer coincides with the downwind prolongation of the pyroclastic flow deposits. These results indicate that the bimodal distribution of grain size in the Tungurahua fall deposit results from synchronous deposition of lapilli from the main plume and fine ash elutriated from scoria flows emplaced on the western flank of the volcano. Our study also reveals that inappropriate grain-size data processing may produce misleading determination of eruptive type. © 2011 Springer-Verlag.

Withers F.,University of Exeter | Dubois M.,CNRS Laboratory of Inorganic Materials | Savchenko A.K.,University of Exeter
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We have fabricated transistor structures using fluorinated single-layer graphene flakes and studied their electronic properties at different temperatures. Compared with pristine graphene, fluorinated graphene has a very large and strongly temperature-dependent resistance in the electroneutrality region. We show that fluorination creates a mobility gap in graphene's spectrum where electron transport takes place via localized electron states. © 2010 The American Physical Society.

Gomes S.,National Graduate School of Chemistry of Clermont Ferrand | Gomes S.,CNRS Laboratory of Inorganic Materials | Nedelec J.-M.,National Graduate School of Chemistry of Clermont Ferrand | Nedelec J.-M.,CNRS Laboratory of Inorganic Materials | And 2 more authors.
Acta Biomaterialia | Year: 2012

Rietveld analysis of X-ray powder diffraction patterns recorded from 28 hydroxyapatite (HAp) samples containing various amounts of zinc (0, 1.6, 3.2 and 6.1 wt.% Zn) and heat treated at various temperatures (between 500°C and 1100°C) has enabled the Zn insertion mechanism into the HAp crystal structure to be finely characterized. The formation of Zn-doped HAp was achieved above 900°C only. Zn-doped HAp has the Ca10Zn x(PO4)6(OH)2-2xO 2x (0 < x ≤ 0.25) chemical composition with a constant Ca/P ratio of 1.67 due to the insertion mechanism into the hexagonal channel (partial occupancy of the 2b Wyckoff site with the formation of linear O-Zn-O entities). Samples heat treated at 500°C were almost single phase, HAp did not incorporate Zn and about half of the Zn atoms incorporated during the synthesis are not observable by X-ray powder diffraction (contained in an amorphous compound or physisorbed at the HAp surface). The reversible formation of Zn-doped β-TCP phase was observed at 600°C, reached its maximum content at 900°C and had almost vanished at 1100°C. The results presented here strengthen the recently described mechanism of Zn insertion in the interstitial 2b Wyckoff position of the HAp structure, and explain the origin of the contradictory reports in the corresponding literature. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Martins S.E.,University of Exeter | Withers F.,University of Exeter | Dubois M.,CNRS Laboratory of Inorganic Materials | Craciun M.F.,University of Exeter | Russo S.,University of Exeter
New Journal of Physics | Year: 2013

We demonstrate a novel method to tune the energy gap ε1 between the localized states and the mobility edge of the valence band in chemically functionalized graphene by changing the coverage of fluorine adatoms via electron-beam irradiation. From the temperature dependence of the electrical transport properties we show that ε1 in partially fluorinated graphene CF0.28 decreases upon electron irradiation up to a dose of 0.08 C cm-2. For low irradiation doses (<0.1 C cm-2) partially fluorinated graphene behaves as a lightly doped semiconductor with impurity bands close to the conduction and valence band edges, whereas for high irradiation doses (>0.2 C cm-2) the electrical conduction takes place via Mott variable range hopping. © IOP Publishing and Deutsche Physikalische Gesellschaft.

Claves D.,University Blaise Pascal | Claves D.,CNRS Laboratory of Inorganic Materials
New Journal of Chemistry | Year: 2011

Fluorocarbon nanostructures possess an outer halogenated crown that plays the role of an interface towards their environment and whose properties are then crucial for anticipating the integration of the latter materials in nanotechnology processes. Therefore, the result of fluorine addition to nanocarbon frames has been investigated here with the help of IR and XPS spectroscopies, and the role played by the pristine lattice curvature and the addend's addition scheme on the physicochemical characteristics of this outermost shell is experimentally established. The relevant paradigm of supposedly ionocovalent C-F terminations in these nanomaterials is shown to be obsolete. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Withers F.,University of Exeter | Bointon T.H.,University of Exeter | Dubois M.,CNRS Laboratory of Inorganic Materials | Russo S.,University of Exeter | Craciun M.F.,University of Exeter
Nano Letters | Year: 2011

We demonstrate the possibility to selectively reduce insulating fluorinated graphene to conducting and semiconducting graphene by electron beam irradiation. Electron-irradiated fluorinated graphene microstructures show 7 orders of magnitude decrease in resistivity (from 1 TΩ to 100 kΩ), whereas nanostructures show a transport gap in the source-drain bias voltage. In this transport gap, electrons are localized, and charge transport is dominated by variable range hopping. Our findings demonstrate a step forward to all-graphene transparent and flexible electronics. © 2011 American Chemical Society.

Taviot-Gueho C.,CNRS Laboratory of Inorganic Materials | Feng Y.,CNRS Laboratory of Inorganic Materials | Faour A.,CNRS Laboratory of Inorganic Materials | Leroux F.,CNRS Laboratory of Inorganic Materials
Dalton Transactions | Year: 2010

Using time-resolved, in situ energy-dispersive X-ray diffraction (EDXRD), the formation of interstratified LDH structures, with alternate interlayer spaces occupied by different anions, have been demonstrated during anion exchange reactions. Novel hybrid LDH nanostructures can thus be prepared, combining the physicochemical properties of two intercalated anions plus those of the LDH host. A general trend is that inorganic-inorganic anion exchange reactions occur in a one-step process while inorganic-organic exchanges may proceed via a second-stage intermediate, suggesting that staging occurs partly as a result of organic-inorganic separation. Yet, other influencing parameters must be considered such as LDH host composition, LDH affinity for different anions and LDH particle size as well as extrinsic parameters like the reaction temperature. Hence, a correlation between the occurrence of staging phenomenon and the difficulty of the exchange of the initial anion is observed, suggesting that staging is needed to overcome the energy barrier in the case of the exchange by organic anions. Notwithstanding the LiAl 2 system, staging has mainly been observed with Zn 2Cr LDH host so far, a peculiar LDH composition with a unique Zn/Cr ratio of two and a local order of the cations within the hydroxide layers. The formation of a higher order-staged intermediate than stage two, observed during the exchange reaction of CO 3 2- or SO 4 2- anions with Zn 2Cr- tartrate, is in favour of a Daumas-Herold model although this model implies a bending of LDH layers. The analysis of the X-ray powder diffraction pattern of Zn 2Cr-Cl/tartrate second-stage intermediate, isolated almost as a pure phase during the exchange of Cl - with tartrate anions in Zn 2Cr LDH, indicates a disorder in the stacking sequence and a relative proportion of the two kinds of interlayers slightly different from 50/50. Besides, the microstructural analysis of the XRD pattern reveals a great reduction of the stacking thickness during the anion exchange process but with no change of the in-plane coherent length, therefore no in-plane deformation of LDH host layers. Finally, the anion exchange properties of Zn 2Cr-Cl/tartrate, investigated by means of EDXRD, show highly selective anion-exchange reactions, leading to the formation of new second-stage intermediates that cannot be prepared starting from the mono-intercalated Zn 2Cr-Cl. This "Zn 2Cr-Cl/tartrate approach" might constitute a new route for the synthesis of various mixed organic-inorganic anions-exchanged forms of LDH. © 2010 The Royal Society of Chemistry.

Stitnpfling T.,CNRS Laboratory of Inorganic Materials | Leroux F.,CNRS Laboratory of Inorganic Materials
Chemistry of Materials | Year: 2010

An original concept based on carbon replica method and adapted on organic/inorganic (O/I) hybrid layered double hydroxide (LDH) assembly is used to impart resulting carbon composites and replicas with interesting electrochemical properties. Thanks to the isomorphous cation substitution possible within the LDH layers, a series of O/I materials are prepared using the emulsifier 2-acrylamido-2-methyl-l-propanesulfonatc acid (AMPS) as a source of carbon and Zn2A1, Co2A1fJ1SFe0.5 and Ni 2A1 as the LDH framework container. The process of carbonization and acid leaching is characterized by in situ X-ray diffractometry, Raman spectroscopy, and the pore formation of the resulting carbon replica by nitrogen adsorption. According to the carbonization/ acid-leaching procedure, the electrochemical behavior is characterized in various aqueous electrolytes, using four salts, including 1.0 M NaNO3,0.5 M Na2SO4.1 M Na2SO3. and 6 M KOH by means of cyclic vol tammetry, galvanostatic mode, and complex impedance spectroscopy. Here, the key facet is the combination of the capacitive behavior of carbon, the pseudo-capacitive response coming from its functionalized surface, as well as redox reactions resulting from the inorganic particles present in the carbon composite and acting as a pore former during the acid leaching. From an optimized potential window of 1.2 V in 1 M Na2SO3, an electric energy of 11.0 W h/kg associated with a power density of 87.75 kW/kg is retrieved at a current density of 10 mA/g for carbon replica obtained from Co2Al 0.5Fe0.5/AMPS. and this is determined to be stable at moderate regime without significant capacitance fading. Meanwhile, a corresponding carbon composite, i.e., before acid leaching, presents over an optimized potential window of 1.8 V, a capacitance per surface unit of 92.6/μF/cm2 at slow scan rate, largely because of the pseudo-capacitance effect, and a reversible redox reaction of 43 mAh/g is obtained at the C/3 regime in galvanostatic mode. Finally, preliminary tests in an asymmetric capacitor give some hints on the versatility of the new innovative approach using elcctrochemically active template, which creates the carbon part with suitable (pseudo)-capacitivc properties, as well as being electronically conductive embedding inorganic redox centers. © 2009 American Chemical Society.

Boutinaud P.,National Graduate School of Chemistry of Clermont Ferrand | Boutinaud P.,CNRS Laboratory of Inorganic Materials | Cavalli E.,University of Parma
Chemical Physics Letters | Year: 2011

An empirical model is proposed to predict the energy position of the metal-to-metal charge transfer (MMCT) bands in closed shell d 0 transition metal complex oxides doped with Bi 3+ or Pb 2+ ions. The model is constructed on the basis of optical data compiled from the literature and from the investigation of the luminescence properties of a series of compounds (titanates, vanadates, niobates, tantalates, molybdates, and zirconates) prepared and characterized in this work. © 2011 Elsevier B.V. All rights reserved.

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