In Situ Experimental Evidence for a Nonmonotonous Structural Evolution with Composition in the Molten LiF−ZrF4 System

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• 作者：Olivier Pauvert ; Didier Zanghi ; Mathieu Salanne ; Christian Simon ; Aydar Rakhmatullin ; Haruaki Matsuura ; Yoshihiro Okamoto ; Franois Vivet ; Catherine Bessada
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：May 20, 2010
• 年：2010
• 卷：114
• 期：19
• 页码：6472-6479
• 全文大小：311K
• 年卷期：v.114,no.19(May 20, 2010)
• ISSN：1520-5207

文摘

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.