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Bulk hexagonal diamond

AI Summary4 min read

TL;DR

Researchers have successfully synthesized millimeter-sized, phase-pure hexagonal diamond (HD) from graphite under high pressure and temperature. This resolves the long-standing controversy over HD's existence and reveals it has slightly higher hardness and thermal stability than cubic diamond.

Key Takeaways

  • •Hexagonal diamond (HD) was synthesized from graphite at high pressure and temperature, providing solid experimental evidence for its existence.
  • •HD exhibits slightly higher hardness and high thermal stability compared to cubic diamond (CD).
  • •The study clarifies the transformation pathway from graphite to HD, offering new insights into carbon phase transitions.
  • •This breakthrough paves the way for future research and potential technological applications of HD.

Tags

Mechanical propertiesPhase transitions and critical phenomenaScienceHumanities and Social Sciencesmultidisciplinary

Abstract

Known as the ‘ultimate semiconductor’, cubic diamond (CD) has gained substantial interest both scientifically and industrially. Its polymorph, hexagonal diamond (HD), is even more intriguing because of its fascinating properties associated with the meteorite impacts1,2,3,4,5,6,7,8. As no solid experimental evidence has been provided to prove its existence, the physical properties of HD remain largely unexplored. Here we report the synthesis of millimetre-sized, phase-pure HD from highly oriented pyrolytic graphite (HOPG) compressed along the c-axis at elevated temperatures. Combining advanced structural characterizations and theoretical simulations, we confirm the identity of HD and clarify the transformation pathway from graphite. Bulk HD exhibits a slightly higher hardness than CD and high thermal stability. These findings resolve the long-standing controversy on the existence of HD as a discrete carbon phase and provide new insight into the graphite-to-diamond phase transition, paving the way for future research and practical use of HD in advanced technological applications.

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Fig. 1: XRD patterns and P–T phase diagram of graphite.
Fig. 2: Atomic structure of the bulk HD recovered from 20 GPa and 1,300 °C.
Fig. 3: Large-scale molecular dynamics simulations of the transformation process from HOPG to HD based on machine learning potential.
Fig. 4: Mechanical and thermal properties of bulk HD.

Data availability

All data supporting the findings of this study are available within this article and its Supplementary Information. Source data are provided with this paper.

References

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