钇基熔融稀土碱金属氟化物的结构和动力学
Structure and dynamics in yttrium-based molten rare earth alkali fluorides
摘要：
采用脉冲场梯度核磁共振谱、电位实验和分子动力学模拟研究了熔融LiF-YF 3混合物的输运性质。计算的扩散系数和电导率与测量结果在很宽的组成范围内进行了比较。然后，我们提取静态（径向分布函数，协调数分布）和动态（笼关联函数）的模拟量。然后，我们讨论了熔盐的微观结构和它们的动力学性质之间的相互作用。通常认为，阴离子扩散系数的变化主要是由其与金属离子（此处为Y3+）的配位演变驱动的。我们比较这个系统与氟锆酸盐熔体，并证明，配位数是一个穷人的扩散系数的演变指标。相反，我们建议使用离子键的寿命。我们发现，在LiF-YF 3中的弱Y-F离子键不诱导预期的趋势的氟化物扩散系数收敛到一个钇阳离子的YF 3含量增加时。的能斯特-爱因斯坦关系估计的电导率的有效性的影响进行了讨论。
英文摘要：
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 accross 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 (Y3+ 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 the one of yttrium cation when the content in YF3 increases. Implications on the validity of the Nernst-Einstein relation for estimating the electrical conductivity are discussed.
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