Conditions Extrêmes et Matériaux : Haute Température et Irradiation

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O.Pauvert, D.Zanghi, M.Salanne, C.Simon, A.Rakhmatullin, H.Matsuura, Y.Okamoto, F.Vivet, C.Bessada, 'In Situ Experimental Evidence for a Nonmonotonous Structural Evolution with Composition in the Molten LiF−ZrF4 System', J. Phys. Chem. B 114 (19) 6472–6479 (2010) doi:10.1021/jp912195j

We propose in this paper an original approach to study the structure of the molten LiF−ZrF4 system up to 50 mol % ZrF4, combining high-temperature nuclear magnetic resonance (NMR) and extended X-ray absorption fine structure (EXAFS) experiments with molecular dynamics (MD) calculations. 91Zr high-temperature NMR experiments give an average coordination of 7 for the zirconium ion on all domains of composition. MD simulations, in agreement with EXAFS experiments at the K-edge of Zr, provide evidence for the coexistence of three different Zr-based complexes, [ZrF6]2−, [ZrF7]3−, and [ZrF8]4−, in the melt; the evolution of the concentration of these species upon addition of ZrF4 is quantified. Smooth variations are observed, apart from a given composition at 35 mol % ZrF4, for which an anomalous point is observed. Concerning the anion coordination, we observe a predominance of free fluorides at low concentrations in ZrF4, and an increase of the number of bridging fluoride ions between complexes with addition of ZrF4.