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<p>Natural and synthetic diamonds mostly have a cubic lattice, whereas a rare hexagonal structure—known as hexagonal diamond (HD)—has been largely unexplored due to the low purity and minuscule size of most samples obtained. The synthesis of HD remains a challenge and even its existence remains controversial. Here we report the synthesis of well-crystallized, nearly pure HD by heating highly compressed graphite, which is applicable to both bulk and nanosized graphitic precursors. Experiments and theoretical analyses show that the formation of a post-graphite phase within compressed graphite and temperature gradients promote HD growth. Using this approach, a millimetre-sized, highly oriented HD block comprising stacked single-crystal-like HD nanolayers is obtained. This HD exhibits high thermal stability up to 1,100 °C and a very high hardness of 155 GPa. Our findings offer valuable insights regarding the graphite-to-diamond conversion under elevated pressure and temperature, providing opportunities for the fabrication and applications of this unique material.</p>

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General approach for synthesizing hexagonal diamond by heating post-graphite phases

  • 期刊论文

  • 发表日期：

    2025年2月10日

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  • Desi Chen,
  • Guwen Chen,
  • Long Lv,
  • Jiajun Dong,
  • Yuchen Shang,
  • Xuyuan Hou,
  • Yan Wang,
  • Jianqi Shang,
  • Saisai Wang,
  • Yankun Yin,
  • Ran Liu,
  • Wei Zhang,
  • Zhou Jiang,
  • Yan He,
  • Bingchen He,
  • Chengwen Mao,
  • Shengcai Zhu,
  • Bertil Sundqvist,
  • Bingbing Liu,
  • Mingguang Yao

摘要

Natural and synthetic diamonds mostly have a cubic lattice, whereas a rare hexagonal structure—known as hexagonal diamond (HD)—has been largely unexplored due to the low purity and minuscule size of most samples obtained. The synthesis of HD remains a challenge and even its existence remains controversial. Here we report the synthesis of well-crystallized, nearly pure HD by heating highly compressed graphite, which is applicable to both bulk and nanosized graphitic precursors. Experiments and theoretical analyses show that the formation of a post-graphite phase within compressed graphite and temperature gradients promote HD growth. Using this approach, a millimetre-sized, highly oriented HD block comprising stacked single-crystal-like HD nanolayers is obtained. This HD exhibits high thermal stability up to 1,100 °C and a very high hardness of 155 GPa. Our findings offer valuable insights regarding the graphite-to-diamond conversion under elevated pressure and temperature, providing opportunities for the fabrication and applications of this unique material.