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<p>Silicon and its composites are key materials owing to their extensive use in the semiconductor industry. While the diamond-structured form dominates, other allotropes with superior properties at ambient conditions remain of interest. Toward this, Si<sub>46</sub> clathrate type-I crystals containing alkali/alkaline-earth metals have been extensively studied, but the experimental observation of a guest-free Si<sub>46</sub> structure has been challenging. Using advanced electron microscopy, we show experimental evidence of guest-free clathrate-I Si<sub>46</sub> framework from Ba<sub>8-<i>x</i></sub>Si<sub>46</sub> under in situ heating. We reveal the stepwise Ba evacuation process, starting with loss of Ba1 from the smaller cages to form Ba<sub>6</sub>Si<sub>46</sub>, followed by removal of Ba2 in larger cages to reach Si<sub>46</sub> that appears in the thin region of the nanocrystal with a thickness around 4-6 nm at 500 °C. Calculations give a quasi-direct bandgap of 1.89 eV and support the preferential evacuation of Ba1. The observation of this guest-free Si<sub>46</sub> framework opens up possibilities for applications in high-speed transistors, optoelectronic devices or solar cell technologies.</p>

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Observation of a guest-free Si46 clathrate-I framework from Ba8-xSi46 upon in situ vacuum heating

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年10月17日

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  • Yi Zhou,
  • Qing Zhang,
  • Alvaro Mayoral,
  • Peter R. Spackman,
  • Takashi Matsumoto,
  • Jun Li,
  • Julian D. Gale,
  • Michael W. Anderson,
  • Hiroshi Fukuoka,
  • Shoji Yamanaka,
  • Osamu Terasaki

摘要

Silicon and its composites are key materials owing to their extensive use in the semiconductor industry. While the diamond-structured form dominates, other allotropes with superior properties at ambient conditions remain of interest. Toward this, Si46 clathrate type-I crystals containing alkali/alkaline-earth metals have been extensively studied, but the experimental observation of a guest-free Si46 structure has been challenging. Using advanced electron microscopy, we show experimental evidence of guest-free clathrate-I Si46 framework from Ba8-xSi46 under in situ heating. We reveal the stepwise Ba evacuation process, starting with loss of Ba1 from the smaller cages to form Ba6Si46, followed by removal of Ba2 in larger cages to reach Si46 that appears in the thin region of the nanocrystal with a thickness around 4-6 nm at 500 °C. Calculations give a quasi-direct bandgap of 1.89 eV and support the preferential evacuation of Ba1. The observation of this guest-free Si46 framework opens up possibilities for applications in high-speed transistors, optoelectronic devices or solar cell technologies.