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Title: Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

We predict mechanochemical formation of heterogeneous diamond structures from rapid uniaxial compression in graphite using quantum molecular dynamics simulations. Ensembles of simulations reveal the formation of different diamondlike products starting from thermal graphite crystal configurations. Here in this paper, we identify distinct classes of final products with characteristic probabilities of formation, stress states, and electrical properties and show through simulations of rapid quenching that these products are nominally stable and can be recovered at room temperature and pressure. Some of the diamond products exhibit significant disorder and partial closure of the energy gap between the highest-occupied and lowest-unoccupied molecular orbitals (i.e., the HOMO-LUMO gap). Seeding atomic vacancies in graphite significantly biases toward forming products with small HOMO-LUMO gap. We show that a strong correlation between the HOMO-LUMO gap and disorder in tetrahedral bonding configurations informs which kinds of structural defects are associated with gap closure. The rapid diffusionless transformation of graphite is found to lock vacancy defects into the final diamond structure, resulting in configurations that prevent sp 3 bonding and lead to localized HOMO and LUMO states with a small gap.
Authors:
 [1] ;  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-749562
Journal ID: ISSN 2469-9950; PRBMDO; 934232
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 97; Journal Issue: 18; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1466945
Alternate Identifier(s):
OSTI ID: 1439136

Kroonblawd, Matthew P., and Goldman, Nir. Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite. United States: N. p., Web. doi:10.1103/PhysRevB.97.184106.
Kroonblawd, Matthew P., & Goldman, Nir. Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite. United States. doi:10.1103/PhysRevB.97.184106.
Kroonblawd, Matthew P., and Goldman, Nir. 2018. "Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite". United States. doi:10.1103/PhysRevB.97.184106.
@article{osti_1466945,
title = {Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite},
author = {Kroonblawd, Matthew P. and Goldman, Nir},
abstractNote = {We predict mechanochemical formation of heterogeneous diamond structures from rapid uniaxial compression in graphite using quantum molecular dynamics simulations. Ensembles of simulations reveal the formation of different diamondlike products starting from thermal graphite crystal configurations. Here in this paper, we identify distinct classes of final products with characteristic probabilities of formation, stress states, and electrical properties and show through simulations of rapid quenching that these products are nominally stable and can be recovered at room temperature and pressure. Some of the diamond products exhibit significant disorder and partial closure of the energy gap between the highest-occupied and lowest-unoccupied molecular orbitals (i.e., the HOMO-LUMO gap). Seeding atomic vacancies in graphite significantly biases toward forming products with small HOMO-LUMO gap. We show that a strong correlation between the HOMO-LUMO gap and disorder in tetrahedral bonding configurations informs which kinds of structural defects are associated with gap closure. The rapid diffusionless transformation of graphite is found to lock vacancy defects into the final diamond structure, resulting in configurations that prevent sp3 bonding and lead to localized HOMO and LUMO states with a small gap.},
doi = {10.1103/PhysRevB.97.184106},
journal = {Physical Review B},
number = 18,
volume = 97,
place = {United States},
year = {2018},
month = {5}
}

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