open access

https://hdl.handle.net/2115/88651

A Novel Technique for Controlling Anisotropic Ion Diffusion : Bulk Single-Crystalline Metallic Silicon Clathrate

英語

type-II silicon clathrate

2022-03-03

Wiley-Blackwell

Advanced Materials

34(9)

2106754

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 mu m. 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 Na24Si136 composed 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.

学術雑誌論文

Accepted Manuscript

This is the peer reviewed version of the following article: [Iwasaki, S., Morito, H., Komine, T., Morita, K., Shibuya, T., Nishii, J., Fujioka, M., A Novel Technique for Controlling Anisotropic Ion Diffusion: Bulk Single-Crystalline Metallic Silicon Clathrate. Adv. Mater. 2022, 34, 2106754. https://doi.org/10.1002/adma.202106754], which has been published in final form at https://doi.org/10.1002/adma.202106754. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.

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