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Title: Investigation on the formation of lonsdaleite from graphite

Abstract

Structural stability and the possible pathways to experimental formation of lonsdaleite—a hexagonal 2H polytype of diamond—have been studied in the framework of the density functional theory (DFT). It is established that the structural transformation of orthorhombic Cmmm graphite to 2H polytype of diamond must take place at a pressure of 61 GPa, while the formation of lonsdaleite from hexagonal P6/mmm graphite must take place at 56 GPa. The minimum potential barrier height separating the 2H polytype state from graphite is only 0.003 eV/atom smaller than that for the cubic diamond. The high potential barrier is indicative of the possibility of stable existence of the hexagonal diamond under normal conditions. In this work, we have also analyzed the X-ray diffraction and electron-microscopic data available for nanodiamonds found in meteorite impact craters in search for the presence of hexagonal diamond. Results of this analysis showed that pure 3C and 2H polytypes are not contained in the carbon materials of impact origin, the structure of nanocrystals found representing diamonds with randomly packed layers. The term “lonsdaleite,” used to denote carbon materials found in meteorite impact craters and diamond crystals with 2H polytype structure, is rather ambiguous, since no pure hexagonal diamond has beenmore » identified in carbon phases found at meteorite fall sites.« less

Authors:
Publication Date:
OSTI Identifier:
22617069
Resource Type:
Journal Article
Journal Name:
Journal of Experimental and Theoretical Physics
Additional Journal Information:
Journal Volume: 124; Journal Issue: 2; Other Information: Copyright (c) 2017 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1063-7761
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; CRYSTALS; DENSITY FUNCTIONAL METHOD; DIAMONDS; ELECTRONS; GRAPHITE; HEXAGONAL LATTICES; LAYERS; METEORITES; NANOSTRUCTURES; ORTHORHOMBIC LATTICES; PRESSURE RANGE GIGA PA; RANDOMNESS; STABILITY; X-RAY DIFFRACTION

Citation Formats

Greshnyakov, V. A., and Belenkov, E. A., E-mail: belenkov@csu.ru. Investigation on the formation of lonsdaleite from graphite. United States: N. p., 2017. Web. doi:10.1134/S1063776117010125.
Greshnyakov, V. A., & Belenkov, E. A., E-mail: belenkov@csu.ru. Investigation on the formation of lonsdaleite from graphite. United States. doi:10.1134/S1063776117010125.
Greshnyakov, V. A., and Belenkov, E. A., E-mail: belenkov@csu.ru. Wed . "Investigation on the formation of lonsdaleite from graphite". United States. doi:10.1134/S1063776117010125.
@article{osti_22617069,
title = {Investigation on the formation of lonsdaleite from graphite},
author = {Greshnyakov, V. A. and Belenkov, E. A., E-mail: belenkov@csu.ru},
abstractNote = {Structural stability and the possible pathways to experimental formation of lonsdaleite—a hexagonal 2H polytype of diamond—have been studied in the framework of the density functional theory (DFT). It is established that the structural transformation of orthorhombic Cmmm graphite to 2H polytype of diamond must take place at a pressure of 61 GPa, while the formation of lonsdaleite from hexagonal P6/mmm graphite must take place at 56 GPa. The minimum potential barrier height separating the 2H polytype state from graphite is only 0.003 eV/atom smaller than that for the cubic diamond. The high potential barrier is indicative of the possibility of stable existence of the hexagonal diamond under normal conditions. In this work, we have also analyzed the X-ray diffraction and electron-microscopic data available for nanodiamonds found in meteorite impact craters in search for the presence of hexagonal diamond. Results of this analysis showed that pure 3C and 2H polytypes are not contained in the carbon materials of impact origin, the structure of nanocrystals found representing diamonds with randomly packed layers. The term “lonsdaleite,” used to denote carbon materials found in meteorite impact craters and diamond crystals with 2H polytype structure, is rather ambiguous, since no pure hexagonal diamond has been identified in carbon phases found at meteorite fall sites.},
doi = {10.1134/S1063776117010125},
journal = {Journal of Experimental and Theoretical Physics},
issn = {1063-7761},
number = 2,
volume = 124,
place = {United States},
year = {2017},
month = {2}
}