A Novel Technique for Controlling Anisotropic Ion Diffusion: Bulk Single‐Crystalline Metallic Silicon Clathrate
A Novel Technique for Controlling Anisotropic Ion Diffusion: Bulk Single‐Crystalline Metallic Silicon Clathrate
复制标题
控制各向异性离子扩散的新技术：块状单晶金属硅包合物
DOI：
10.1002/adma.202106754
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发表时间：
2022
影响因子：
29.4
通讯作者：
Fujioka Masaya
中科院分区：
文献类型：
--
作者：
Iwasaki Suguru;Morito Haruhiko;Komine Takashi;Morita Kazuki;Shibuya Taizo;Nishii Junji;Fujioka Masaya
无钠硅笼合物是金刚石结构硅的一种同素异形体，只由硅笼组成。这种材料在各种器件应用中很有前途，例如下一代光伏。合成无钠硅笼合物的可能技术是从Na24Si136的硅笼中提取Na+。真空退火法是目前公认的一种传统有效的提钠方法。然而，这项研究表明，在超过150微米的区域内，无法从单晶II类金属硅笼(Na24Si136)的表面提取Na+。因此，开发了一种新的方法来控制各向异性离子扩散：这对各种组成元素之间键合强度差异很大的化合物是有效的，例如由共价硅笼组成的Na24Si136和弱捕获的Na+。通过巧妙地利用化学势的差异作为驱动力，无论单晶的大小如何，都可以均匀地提取Na+，同时保持高结晶度。此外，还用密度泛函理论对所提出的点缺陷模型进行了评价，并解释了Na+在硅笼之间的迁移。预计所发展的实验和计算技术将极大地促进合成热力学亚稳态材料的材料设计。
Na‐free Si clathrates consisting only of Si cages are an allotrope of diamond‐structured Si. This material is promising for various device applications, such as next‐generation photovoltaics. The probable technique for synthesizing Na‐free Si clathrates is to extract Na+from the Si cages of Na24Si136. Vacuum annealing is presently a well‐known conventional and effective approach for extracting Na. However, this study demonstrates that Na+cannot be extracted from the surface of a single‐crystalline type‐II metallic Si clathrate (Na24Si136) in areas deeper than 150 µm. Therefore, a novel method is developed to control anisotropic ion diffusion: this is effective for various compounds with a large difference in the bonding strength between their constituent elements, such as Na24Si136composed of covalent Si cages and weakly trapped Na+. By skillfully exploiting the difference in the chemical potentials as a driving force, Na+is homogeneously extracted regardless of the size of the single crystal while maintaining high crystallinity. Additionally, the proposed point defect model is evaluated via density functional theory, and the migration of Na+between the Si cages is explained. It is expected that the developed experimental and computational techniques would significantly advance material design for synthesizing thermodynamically metastable materials.