Anne-Laure Rollet

University of Oxford, Oxford, ENG, United Kingdom

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Publications (30)71.62 Total impact

  • Anne-Laure Rollet, Haruaki Matsuura, Catherine Bessada
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    ABSTRACT: The local structure of molten LaF3-LiF-Li2O has been investigated by high temperature NMR spectroscopy. The (139)La and (19)F chemical shifts have been measured as a function of temperature and composition. The NMR spectra show that Li2O reacts completely with LaF3 to form a LaOF compound in the solid state below the melting temperature of the sample. LaOF is not completely dissolved in the fluoride melt and solid LaOF is observed in the (19)F spectra for Li2O concentrations above 10 mol%. We discuss the local environment of lanthanum ions in molten LaF3-LiF-Li2O and compare the results to those with the LaF3-LiF-CaO system. The analysis of the temperature and Li2O concentration dependences of the (139)La and (19)F chemical shifts suggests that several kinds of lanthanum oxyfluoride long-lived LaOxFy(3-x-y) units are present in the melt.
    Dalton transactions (Cambridge, England : 2003). 05/2014;
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    ABSTRACT: Pierre Turq has made decisive contributions to the theory and to the multiscale simulation of charged systems, such as molten salts, electrolyte solutions and colloidal suspensions, in the bulk, at interfaces and under confinement. His research line focussed on dynamical properties and was characterised by constant efforts to connect his theoretical work to both experiments and practical applications. In this article, his colleagues and former students pay a tribute to his past and current research interests by illustrating some recent developments accomplished in his laboratory.
    Molecular Physics 05/2014; 112. · 1.67 Impact Factor
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    ABSTRACT: The transport properties of molten LiF-YF3 mixtures have been studied by pulsed field gradient nuclear magnetic resonance spectroscopy, potentiometric experiments, and molecular dynamics simulations. The calculated diffusion coefficients and electric conductivities compare very well with the measurements across a wide composition range. We then extract static (radial distribution functions, coordination numbers distributions) and dynamic (cage correlation functions) quantities from the simulations. Then, we discuss the interplay between the microscopic structure of the molten salts and their dynamic properties. It is often considered that variations in the diffusion coefficient of the anions are mainly driven by the evolution of its coordination with the metallic ion (Y(3+) here). We compare this system with fluorozirconate melts and demonstrate that the coordination number is a poor indicator of the evolution of the diffusion coefficient. Instead, we propose to use the ionic bonds lifetime. We show that the weak Y-F ionic bonds in LiF-YF3 do not induce the expected tendency of the fluoride diffusion coefficient to converge toward one of the yttrium cation when the content in YF3 increases. Implications on the validity of the Nernst-Einstein relation for estimating the electrical conductivity are discussed.
    The Journal of Chemical Physics 05/2013; 138(18):184503. · 3.12 Impact Factor
  • Anne-Laure Rollet, Catherine Bessada
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    ABSTRACT: This chapter presents the nuclear magnetic resonance (NMR) developments and studies on the high temperature inorganic molten salts and on room temperature ionic liquids. It is focused on the liquid structure investigated, thanks to the chemical shifts analysis and to magnetization transfer experiments. It deals also with the dynamics at the local scale investigated using relaxometry and at the long range using pulsed field gradient NMR.
    Annual Reports on NMR Spectroscopy 01/2013; 78:149-207. · 1.42 Impact Factor
  • Anne-Laure Rollet, Emmanuel Veron, Catherine Bessada
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    ABSTRACT: In this paper we address the effects of fission products on the speciation in molten fluoride salts. Numerous systems with cross-connections have been investigated in order to better identify the influence of CsF in a fluoride melt containing rare earth and oxides : LaF3–AF (A = Li, Na, K, Rb and Cs), LaF3–LiF–CsF, LaF3–LiF–CaF2, LaF3–LiF–CaO, LaF3–LiF–CaO–CsF. In this goal, we performed high temperature NMR experiments and followed in situ the evolution of 19F, 23Na, 85Rb, 133Cs and 139La NMR chemical shifts. In LaF3–AF–CsF and LaF3–AF–CaF2 systems, the coordination number of lanthanum cation ranges from 6 to 8 depending on the LaF3 concentration and on the polarizability of the other cations. The addition of oxide (CaO) in the latter mixtures leads to the formation of lanthanum oxyfluoride species that precipitate in LaOF when CaO concentration is increased. The addition of CsF to LaF3–LiF–CaO yields to a displacement of the dissolved versus precipitated LaOF proportion.
    Journal of Nuclear Materials 10/2012; 429(s 1–3):40–47. · 2.02 Impact Factor
  • Anne-Laure Rollet, Mathieu Salanne, Henri Groult
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    ABSTRACT: The electrical conductivities of molten LiF–YF3 and LiF–NaF–ZrF4 have been obtained from impedance measurements and molecular dynamics simulations, and discussed through the analysis of the local structure of the liquid. The conductivity decreases with addition of MFn (Mn+ = Y3+ or Zr4+) in the melt due to the formation of MFxn−x units, which can be either isolated or linked via bridging fluorine. Structural differences have been put in evidence depending on the nature of the multivalent metallic species (Y3+ and Zr4+) added in the alkali fluoride solvent regarding the stability of the MFxn−x units and the length m of [MFxn−x]m chains. These differences are at the origin of a more pronounced decrease of the electrical conductivity in the Zr-containing fused salts in the low MFn concentration régime.
    Journal of Fluorine Chemistry 08/2012; 134:44–48. · 1.94 Impact Factor
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    ABSTRACT: The synthesis and structure resolution of RbLaF(4) are described. RbLaF(4) is synthesized by solid-state reaction between RbF and LaF(3) at 425 °C under a nonoxidizing atmosphere. Its crystal structure has been resolved by combining neutron and synchrotron powder diffraction data refinements (Pnma,a = 6.46281(2) Å, b = 3.86498(1) Å, c = 16.17629(4) Å, Z = 4). One-dimensional (87)Rb, (139)La, and (19)F MAS NMR spectra have been recorded and are in agreement with the proposed structural model. Assignment of the (19)F resonances is performed on the basis of both (19)F-(139)La J-coupling multiplet patterns observed in a heteronuclear DQ-filtered J-resolved spectrum and (19)F-(87)Rb HMQC MAS experiments. DFT calculations of both the (19)F isotropic chemical shieldings and the (87)Rb, (139)La electric field gradient tensors using the GIPAW and PAW methods implemented in the CASTEP code are in good agreement with the experimental values and support the proposed structural model. Finally, the conductivity of RbLaF(4) and luminescence properties of Eu-doped LaRbF(4) are investigated.
    Inorganic Chemistry 02/2012; 51(4):2272-82. · 4.59 Impact Factor
  • Anne-Laure Rollet, Mathieu Salanne
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    ABSTRACT: This review covers the local structure of molten metal halide, where a somewhat wide definition of “local structure” is employed, i.e. from the first shell of interacting neighbours up to correlations arising at the nanometer length scale. These particular liquids are indeed strongly organized at unusually long distances due to the predominance of coulombic interactions. Many of them are also characterized by the formation of intermediate range ordering. It is therefore impossible to describe the local structure of these liquids omitting this longer-ranged correlation. Finally, a deeper attention is given to the systems on which recent progresses have been made in the last decade, as for instance molten fluorides and rare earth halides.
    Annual Reports Section C"" (Physical Chemistry)""" 06/2011; 107:88-123.
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    ABSTRACT: Measuring internuclear distances through dipolar interaction is a major challenge for solid-state nuclear magnetic resonance (NMR) spectroscopy. Obtaining reliable interatomic distances provides an access to the local structure in ordered or disordered solids. We show that at magic angle spinning (MAS) frequencies larger than ca. 50 kHz, some of the three-spin terms of the homogeneous homonuclear dipolar Hamiltonian can be used to promote the creation of double-quantum coherences between neighbouring (1)H or (19)F spins without using dipolar recoupling pulse sequences in the Dipolar Homonuclear Homogeneous Hamiltonian (DH(3)) double-quantum/single-quantum correlation experiment. This makes it possible to probe inter-nuclear spatial proximity with limited risk of probe or sample damage from radio-frequency (RF) irradiation, and is fully appropriate for fast repetition rate offering sensitivity gains in favourable cases. Experimental demonstrations are supported by multi-spin numerical simulations, which points to new possibilities for the characterization of spin-system geometries.
    Physical Chemistry Chemical Physics 03/2011; 13(17):8024-30. · 4.20 Impact Factor
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    ABSTRACT: We have developed a new experimental setup for the measurement of self-diffusion coefficients at high temperature (up to 1500K) in corrosive liquids. It is based on pulsed field gradient NMR using a 10mm liquid probe with two channels F-H/X modified and coupled with laser heating. The values obtained thanks to this setup are in good agreement with the available data obtained using the reference method, i.e., the capillary method. We present here results on 19F, 7Li, 23Na, 27Al in molten fluorides. In alkali fluoride mixtures, the self-diffusion coefficients depend weakly on the composition (nature and concentration of the different alkali) but mainly on temperature. In cryolite (Na3AlF6), the diffusion evidences AlFx3−x species.
    Comptes Rendus Chimie 04/2010; 13(4):399-404. · 1.92 Impact Factor
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    ABSTRACT: Dialkylimidazolium chlorometallate molten salts resulting from the combination of zirconium or hafnium tetrachloride and 1-butyl-3-methylimidazolium chloride, [C(1)C(4)Im][Cl], have been prepared with a molar fraction of MCl(4), R = n(MCl4)/n(MCl4) + n([C1C4IM][Cl]) equal to 0, 0.1, 0.2, 0.33, 0.5, 0.67. The structure and composition were studied by Differential Scanning Calorimetry (DSC), (35)Cl (263 to 333 K), (1)H and (13)C solid state and solution NMR spectroscopy, and electrospray ionisation (ESI) mass spectrometry. The primary anions of the MCl(4)-based ILs were [MCl(5)], [MCl(6)] and [M(2)Cl(9)], whose relative abundances varied with R. For R = 0.33, pure solid [C(1)C(4)Im](2)[MCl(6)], for both M = Zr and Hf are formed (m.p. = 366 and 385 K, respectively). For R = 0.67 pure ionic liquids [C(1)C(4)Im][M(2)Cl(9)] for both M = Zr and Hf are formed (T(g) = 224 and 220 K, respectively). The thermal dissociation has been attempted of [C(1)C(4)Im](2)[HfCl(6)], and [C(1)C(4)Im](2)[ZrCl(6)] monitored by (35)Cl and (91)Zr solid NMR (high temperature up to 551 K).
    Dalton Transactions 02/2010; 39(5):1379-88. · 4.10 Impact Factor
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    ABSTRACT: The local structure and the dynamics of molten LiF-KF mixtures have been studied by nuclear magnetic resonance (NMR) and molecular dynamics simulations. We have measured and calculated the self-diffusion coefficients of fluorine, lithium and potassium across the full composition range around the liquidus temperature and at 1123 K. Close to the liquidus temperature, D(F), D(Li) and D(K) change with composition in a way that mimics the phase diagram shape. At 1123 K D(F), D(Li) and D(K) depend linearly on the LiF molar fraction. These results show that the composition affects the self-diffusion of anions and cations more weakly than the temperature. The activation energy for diffusion was also determined and its value can be correlated with the strength of the anion-cation interaction in molten fluoride salts.
    Physical Chemistry Chemical Physics 12/2009; 11(48):11501-6. · 4.20 Impact Factor
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    ABSTRACT: Self-diffusion is a fundamental property of liquid dynamics that also provides important structural information. To explore the dynamics in inorganic melts with high liquidus temperature, we propose a new setup based on pulsed field gradient NMR combined with laser heating that makes possible in situ self-diffusion coefficient measurements up to 1500 K. Applied to several corrosive molten fluorides in a wide range of compositions and temperature, we have evidenced the different key parameters of their motion along with their structural characteristics. In alkali fluorides, the self-diffusion coefficient of fluorine depends slightly on the composition compared to the temperature, displaying these systems as an ideal bath of polarizable hard spheres. In contrast, self-diffusion in rare earth and alkali fluorides mixtures presents a complicated balance between temperature and the network-forming process of the ionic long-lived units. These results open wide perspectives in the study of high temperature liquids.
    Inorganic Chemistry 10/2009; 48(23):10972-5. · 4.59 Impact Factor
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    ABSTRACT: In situ high temperature nuclear magnetic resonance in molten fluoride mixtures gives some structural picture of the complexes existing in the melt, i.e. of their nature and relative proportion. Thanks to the development of a laser heating system associated with a close crucible in boron nitride, we can describe experimentally the evolution of these complexes from the anions and the cations point of view. By 19F NMR, we have shown the existence of three kinds of fluorine atoms depending on the composition: free fluorine like in pure LiF (non-bonded), bridging fluorine in melts rich in LnF3 in addition with terminal fluorine singly bonded to one rare earth. Data obtained by NMR spectroscopy are also combined with EXAFS measurements, again thanks to a specific development of the sample holder adapted with molten fluorides and high temperature. This study is a part of our systematic investigation of the different Alk–LnF3 systems by NMR and EXAFS spectroscopy.
    Journal of Fluorine Chemistry 01/2009; 130(1):45-52. · 1.94 Impact Factor
  • Anne-Laure Rollet, Stéphanie Godier, Catherine Bessada
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    ABSTRACT: The local structures of molten lanthanum alkali fluoride binaries have been studied using HT NMR technique. The chemical shifts of (19)F, (23)Na and (139)La in solid and in liquid have been compared for AF (A = alkali) and LaF(3). In pure molten alkali fluorides, the polarisability of anion-cation pairs appears to be a key parameter to depict the observed evolution of (19)F chemical shifts. The influence of the composition has also been studied by measuring the chemical shifts in molten LaF(3)-AF as a function of LaF(3) concentration. A strong influence of the alkali influence is observed. The coordination number of lanthanum is decreased versus AF amount all the more since the alkali atomic number is high. Moreover, the more polarisable the alkali, the less bridging fluorines between the LaF(x) units.
    Physical Chemistry Chemical Physics 07/2008; 10(22):3222-8. · 4.20 Impact Factor
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    ABSTRACT: We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.3 to 30 mol %). Unexpected variations have been observed. The self-diffusion coefficient of every species increases with the quantity of water but not in the same order of magnitude. Whereas very similar evolutions are observed for the anion and cation, the increase is 25 times greater for water molecules. We interpret our data by the existence of phase separation at microscopic scale.
    The Journal of Physical Chemistry B 11/2007; 111(41):11888-91. · 3.61 Impact Factor
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    Photon Factory Activity Report 2007 Part B. 05/2007; 25:26.
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    ABSTRACT: The objective of this paper is to describe the local structure in fluoride melts of nuclear interest. Our experimental approach combines NMR and EXAFS spectroscopies both sensitive to the microstructure of solid and liquid materials. These techniques allow identifying the complex formation in molten media. Thanks to the development of specific cells adapted to molten fluorides up to 1300 °C, we give some structural description of LiF–LnF3 systems (Ln = Y, Lu, Ce) and discuss the evolution of 19F spectra in terms of different fluorine configurations depending on the composition. This approach is further extended to the characterization of LiF–ThF4 system by 19F NMR in melts from 0 to 100 mol% ThF4 at temperatures ranging from 600 to 1100 °C. We report also very first EXAFS spectra obtained in situ at high temperature, at the Thorium LIII edge, in LiF–ThF4 molten mixtures.
    Journal of Nuclear Materials 01/2007; 360(1):43-48. · 2.02 Impact Factor
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    ABSTRACT: The developments of NMR spectroscopy at high temperature now allow us to study in situ a great number of molten materials. This technique is sensitive to local environment around the nucleus, and gives selective and quantitative information not limited by the disorder existing in liquids. NMR can thus provide a microscopic approach of the structure and dynamics of molten compounds by means of knowledge of different species existing in the melt, the average coordination, or nature of the first neighbors. We present high temperature NMR approach of molten fluoride systems of nuclear interest and description of the local structure around each nucleus, and its evolution with the composition.
    Comptes Rendus Chimie 03/2006; 9(3-4):374-380. · 1.92 Impact Factor
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    ABSTRACT: A casting process has been studied for charged polymers: the sulfonated polyimide ionomer membrane. The formation of the membrane has been followed by X-ray reflectivity as a function of temperature. The effect of equivalent weight has been also investigated. The thickness loss presents two regimes: the first one is linear vs time indicating that the models developed for noncharged polymer may be suitable for ionomers in the early period of drying. The second one corresponds to the loss of X-ray reflectivity signal. Moreover, the X-ray reflectivity signal seems to be correlated to the characteristic time of the sample drying. In complement, we have studied the influence of casting on the properties of the dried ionomer membranes. The transport coefficients of N(CH(3))(4)(+) ions confined in two kinds of membranes that were differently cast were measured. The results show that shearing the ionomer solution during casting may lead to an enhancement of the anisotropy of structure and of transport. Moreover, we have studied the effect of both interfaces on the ion transport properties through the dried membranes.
    The Journal of Physical Chemistry B 07/2005; 109(22):11332-9. · 3.61 Impact Factor

Publication Stats

157 Citations
71.62 Total Impact Points

Institutions

  • 2013
    • University of Oxford
      • Department of Materials
      Oxford, ENG, United Kingdom
  • 2012–2013
    • Polytech Paris-UPMC
      Lutetia Parisorum, Île-de-France, France
  • 2007–2012
    • CNRS Orleans Campus
      Orléans, Centre, France
  • 2000–2011
    • Pierre and Marie Curie University - Paris 6
      • Laboratoire Arago
      Lutetia Parisorum, Île-de-France, France
  • 2010
    • University of Lyon
      Lyons, Rhône-Alpes, France