About hopping mechanism for sodium diffusion in silicate liquids with low sodium concentrations: Molecular dynamics simulation
About hopping mechanism for sodium diffusion in silicate liquids with low sodium concentrations: Molecular dynamics simulation
复制标题
关于低钠硅酸盐液体中钠扩散的跳跃机制：分子动力学模拟
DOI：
10.1016/j.molliq.2020.113834
复制
发表时间：
2020
影响因子：
6
通讯作者：
L. San
中科院分区：
文献类型：
--
作者：
P. K. Hung;N. V. Yên;L. T. Vinh;F. Noritake;N. Ha;L. San
在常压、1873K下对Na2O.4SiO2熔体进行了分子动力学模拟，模拟结果表明Na原子位于O多面体中，而不是Si多面体中。此外，总Na的75.86％放置在NBO和FO（非桥接和游离氧）多面体中，其体积为模拟盒的27.36％。我们提出了一种新的钠扩散机制。因此，Na与停留在同一多面体中的网络形成体（O和Si）共同移动，并且经常在不同多面体之间置换。第二种运动类型对钠扩散率做出了重要贡献，并导致非常快的钠迁移率。当 NBO↔BO 发生时，O 多面体之间重新分布的 Na 原子与网络形成者一起进行集体运动。每个BO（桥接氧）、NBO多面体分别有1个和2个位点。 Na位于BO位点的位点能量大于NBO位点，并且Na从当前位点移动到邻近BO位点的跃迁能量大于移动到NBO位点的跃迁能量。啤酒花在低温下彼此之间具有很强的相关性。此外，发现动态结构是异质的。在 150ps 期间，系统包括由 Sisingle bondO 子网和 Osingle bondO 集群占据的两个不同区域。 Osingle bondO簇占据的区域类似于钠的优先扩散路径，其体积为模拟盒的20.5%。
Molecular dynamics simulation is done for Na2O.4SiO2melt at ambient pressure and 1873 K. The simulation shows that Na atoms are placed in O polyhedrons and not in Si ones. Moreover, 75.86% of total Na are placed in NBO and FO (non-bridging and free oxygen) polyhedrons, the volume of which is 27.36% of simulation box. We propose a new mechanism for sodium diffusion. Accordingly, Na moves collectively with network formers (O and Si) staying in the same polyhedron, and frequently displaces between different polyhedrons. The second motion type gives the essential contribution to sodium diffusivity, and leads to very fast sodium mobility. As NBO ↔ BO happens, Na atoms redistributed between O polyhedrons make the collective motion with network formers. Each BO (bridging oxygen), NBO polyhedron has 1 and 2 sites, respectively. The site energy for Na located in BO site is larger than NBO site, and the transition energy for Na moving from present site to neighboring BO site is larger than the one to NBO site. The hops are strongly correlated with each other at low temperature. Furthermore, the dynamical structure is found to be heterogeneous. During 150 ps, the system comprises two distinct regions occupied by Sisingle bondO subnet and Osingle bondO cluster. The region occupied by Osingle bondO cluster resembles a preferential diffusion pathway for sodium, the volume of which is 20.5% of simulation box.