Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond

• Published in: Nature communications Vol. 4; no. 1; p. 2343
• Main Authors: Tanigaki, Kenichi, Ogi, Hirotsugu, Sumiya, Hitoshi, Kusakabe, Koichi, Nakamura, Nobutomo, Hirao, Masahiko, Ledbetter, Hassel
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12-08-2013; Nature Publishing Group
• Subjects: 639/301/1023/303; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3343

Diamond is the stiffest known material. Here we report that nanopolycrystal diamond synthesized by direct-conversion method from graphite is stiffer than natural and synthesized monocrystal diamonds. This observation departs from the usual thinking that nanocrystalline materials are softer than their monocrystals because of a large volume fraction of soft grain-boundary region. The direct conversion causes the nondiffusional phase transformation to cubic diamond, producing many twins inside diamond grains. We give an
ab initio-
calculation twinned model that confirms the stiffening. We find that shorter interplane bonds along [111] are significantly strengthened near the twinned region, from which the superstiff structure originates. Our discovery provides a novel step forward in the search for superstiff materials.
Monocrystalline diamond is the stiffest and hardest material known to man. Here, the authors reveal that polycrystalline diamond synthesized by a direct-conversion method from graphite displays higher elastic constants than its monocrystalline counterpart.