One-dimensional water channels in lanthanum sulfate: a first-principles study
One-dimensional water channels in lanthanum sulfate: a first-principles study
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DOI：
10.1039/c7ta05714h
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发表时间：
2017-10-14
影响因子：
11.9
通讯作者：
Uda, Tetsuya
中科院分区：
文献类型：
--
作者：
Toyoura, Kazuaki;Tai, Hirotaka;Uda, Tetsuya
基于密度泛函理论（DFT），从第一性原理的角度分析了水在硫酸镧La-2(SO4)(3)中的稳定结构和扩散机理。第一性原理分子动力学（firstprinciples molecular dynamics， FPMD）模拟表明，硫酸盐晶体中的水在保持水分子形状的情况下溶解和迁移。在模拟过程中，观察到水扩散的3个基本过程（路径1 ~ 3），通过势能面（PES）映射计算出它们的势垒分别为0.27、0.81和1.50 eV。具有最低势垒的路径1只是相邻位点之间的振荡传递，而具有第二低势垒的路径2在[010]方向上形成一维（1D）水通道。在523 K时，沿通道的水扩散率估计为10(-10)cm(2) s(-1)，导致扩散长度在几分钟内达到微米范围。这表明，La-2(SO4)(3)的快速水化/脱水反应不仅归因于体中的一维水通道，还归因于小晶粒尺寸和高晶界扩散率。
The stable structure and diffusion mechanism of water in lanthanum sulfate La-2(SO4)(3) have been theoretically analyzed in a first-principles manner based on the density functional theory (DFT). The firstprinciples molecular dynamics (FPMD) simulation indicates that water in the sulfate crystal is dissolved and migrates with maintaining the shape of the water molecule. In this simulation, three elementary processes for water diffusion were observed (paths 1-3), whose potential barriers were calculated to be 0.27, 0.81, and 1.50 eV, respectively, by potential energy surface (PES) mapping. Path 1 with the lowest potential barrier is only oscillatory transfer between adjacent sites, while path 2 with the second-lowest potential barrier forms one-dimensional (1D) water channels in the [010] direction. The water diffusivity along the channels is estimated to be similar to 10(-10) cm(2) s(-1) at 523 K, leading to a diffusion length in the micrometer range within a few minutes. This suggests that the reported fast hydration/dehydration reaction of La-2(SO4)(3) should be attributed not only to the 1D water channels in the bulk but also to the small crystal grain size and the high grain boundary diffusivity.