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Title: Nanocrystalline hexagonal diamond formed from glassy carbon

Carbon exhibits a large number of allotropes and its phase behaviour is still subject to signifcant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defned material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100GPa and 400 C. The nanocrystalline material was recovered at ambient and analysed using difraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic fow under compression in the diamond anvil cell, which lowers the energy barrier by locking in favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by frst principles calculations of transformation pathways and explains why the new phase is found in an annular region. Furthermore, our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoriticmore » impacts.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [5]
  1. The Australian National Univ., Canberra, ACT (Australia)
  2. RMIT Univ., Melbourne, VIC (Australia)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Carnegie Institute of Washington, Washington, D.C. (United States)
  5. The Univ. of Sydney, NSW (Australia)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2045-2322
Nature Publishing Group
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
36 MATERIALS SCIENCE; phase transitions and critical phenomena; structure of solids and liquids
OSTI Identifier: