Silicon Framework-Based Lithium Silicides at High Pressures

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• 作者：Shoutao Zhang ; Yanchao Wang ; Guochun Yang ; Yanming Ma
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：July 6, 2016
• 年：2016
• 卷：8
• 期：26
• 页码：16761-16767
• 全文大小：589K
• 年卷期：0
• ISSN：1944-8252

文摘

The bandgap and optical properties of diamond silicon (Si) are not suitable for many advanced applications such as thin-film photovoltaic devices and light-emitting diodes. Thus, finding new Si allotropes with better bandgap and optical properties is desirable. Recently, a Si allotrope with a desirable bandgap of ∼1.3 eV was obtained by leaching Na from NaSi₆ that was synthesized under high pressure [Nat. Mater. 2015, 14, 169], paving the way to finding new Si allotropes. Li is isoelectronic with Na, with a smaller atomic core and comparable electronegativity. It is unknown whether Li silicides share similar properties, but it is of considerable interest. Here, a swarm intelligence-based structural prediction is used in combination with first-principles calculations to investigate the chemical reactions between Si and Li at high pressures, where seven new compositions (LiSi₄, LiSi₃, LiSi₂, Li₂Si₃, Li₂Si, Li₃Si, and Li₄Si) become stable above 8.4 GPa. The Si—Si bonding patterns in these compounds evolve with increasing Li content sequentially from frameworks to layers, linear chains, and eventually isolated Si ions. Nearest-neighbor Si atoms, in Cmmm-structured LiSi₄, form covalent open channels hosting one-dimensional Li atom chains, which have similar structural features to NaSi₆. The analysis of integrated crystal orbital Hamilton populations reveals that the Si—Si interactions are mainly responsible for the structural stability. Moreover, this structure is dynamically stable even at ambient pressure. Our results are also important for understanding the structures and electronic properties of Li—Si binary compounds at high pressures.