X-ray and molecular dynamics study of the temperature-dependent structure of FLiNaK
X-ray and molecular dynamics study of the temperature-dependent structure of FLiNaK
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FLiNaK 温度依赖性结构的 X 射线和分子动力学研究
DOI：
10.1016/j.nme.2023.101530
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发表时间：
2023
影响因子：
2.6
通讯作者：
Condon, Nicholas
中科院分区：
文献类型：
--
作者：
Guo, Jicheng;Zhang, Yifan;Ludwig, Karl;Yan, Haoxuan;Levy, Alexander;Wadehra, Anubhav;Gao, Michael C.;Benmore, Chris;Rose, Melissa;Condon, Nicholas
在460 - 636 ° C的温度范围内，用X射线散射和分子动力学（MD）模拟研究了FLiNaK的原子结构及其随温度的演变。与之前的研究雅阁，观察到平均最近邻（NN）阳离子-阴离子配位数随着阳离子尺寸的增加而增加，从Li-F的1.44增加到K-F的1.64。此外，我们还发现了局部配位几何的耦合变化-从Li-F的四面体到Na的八面体再到K的非常无序的准立方。阳离子-阴离子对的不同几何形状和配位距离导致相对恒定的F-F次近邻（NNN）距离约为3.1 μ m。这种相对固定的距离允许F阴离子假设一个整体的相关结构非常类似于一个硬球液体的扩展半径，这是超出正常的F离子的大小，但反映了阳离子-阴离子配位的要求。仔细考虑实验原子分布函数随温度升高的演变表明，在每个距离的相关性的变化可以理解的范围内扩大不对称的邻居分布。在所研究的温度范围内，随着温度的升高，F-F相关性的演变与硬球液体中由于密度降低而引起的预期变化一致。
The atomic structure of FLiNaK and its evolution with temperature are examined with x-ray scattering and molecular dynamics (MD) simulations in the temperature range 460–636 °C. In accord with previous studies, it’s observed that the average nearest-neighbor (NN) cation-anion coordination number increases with increasing cation size, going from ∼4 for Li-F to ∼6.4 for K-F. In addition, we find that there is a coupled change in local coordination geometry – going from tetrahedral for Li-F to octahedral for Na to very disordered quasi-cuboidal for K. The varying geometry and coordination distances for the cation-anion pairs cause a relatively constant F-F next-nearest neighbor (NNN) distance of approximately 3.1 Å. This relatively fixed distance allows the F anions to assume an overall correlated structure very similar to that of a hard-sphere liquid with an extended radius which is beyond the normal F ion size but reflects the cation-anion coordination requirements. Careful consideration of the evolution of the experimental atomic distribution functions with increasing temperature shows that the changes in correlation at each distance can be understood within the context of broadening asymmetric neighbor distributions. Within the temperature range studied, the evolution of F-F correlations with increasing temperature is consistent with changes expected in a hard-sphere liquid simply due to decreasing density.