A new hard allotropic form of carbon: Dream or reality?

Konyashin, I.; Khvostov, V. V.; Babaev, V. G.; Гусева, М. Б.; Mayer, J.; Sirenko, A. A.

doi:10.1016/j.ijrmhm.2005.04.015

Cited by 26 publications

(26 citation statements)

References 22 publications

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“…Also reported in YD-boundary deposits (15,16) is the proposed n-diamond (or fcc carbon) modification of diamond; see (31,32). No n diamond was observed in any of our specimens.…”

Section: Resultssupporting

confidence: 57%

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Daulton

Pinter

Scott

2010

Proc. Natl. Acad. Sci. U.S.A.

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The causes of the late Pleistocene megafaunal extinctions in North America, disappearance of Clovis paleoindian lithic technology, and abrupt Younger-Dryas (YD) climate reversal of the last deglacial warming in the Northern Hemisphere remain an enigma. A controversial hypothesis proposes that one or more cometary airbursts/ impacts barraged North America ≈12,900 cal yr B.P. and caused these events. Most evidence supporting this hypothesis has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype) in Bølling-Ållerod-YD-boundary sediments. The hexagonal polytype of diamond, lonsdaleite, is of particular interest because it is often associated with shock pressures related to impacts where it has been found to occur naturally. Unfortunately, previous reports of YD-boundary nanodiamonds have left many unanswered questions regarding the nature and occurrence of the nanodiamonds. Therefore, we examined carbon-rich materials isolated from sediments dated 15,818 cal yr B.P. to present (including the Bølling-Ållerod-YD boundary). No nanodiamonds were found in our study. Instead, graphene-and graphene/ graphane-oxide aggregates are ubiquitous in all specimens examined. We demonstrate that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond. Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.archaeology | paleoclimate | Quaternary extinctions | carbon spherules | fungal sclerotia

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“…Also reported in YD-boundary deposits (15,16) is the proposed n-diamond (or fcc carbon) modification of diamond; see (31,32). No n diamond was observed in any of our specimens.…”

Section: Resultssupporting

confidence: 57%

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Daulton

Pinter

Scott

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…To confirm reliability of our structure, the ELNES and Raman of HR -carbon was calculated and compared with the experimental results 32 38 . The ELNES spectra are very useful to distinguish the various hybridized covalent bonds in carbon materials.…”

Section: Resultsmentioning

confidence: 88%

“…Interestingly, some forbidden reflections of cubic diamond have also been observed at the same time in experiments. The n-diamond was initially thought to be a face-central cubic modified diamond (Fcc carbon) 31 32 38 39 40 . However, theoretical calculations indicate that the Fcc carbon is less stable than the other candidate phases 41 42 43 .…”

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confidence: 99%

Ab initio structure determination of n-diamond

Tian

Chu

et al. 2015

Sci Rep

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A systematic computational study on the crystal structure of n-diamond has been performed using first-principle methods. A novel carbon allotrope with hexagonal symmetry R32 space group has been predicted. We name it as HR-carbon. HR-carbon composed of lonsdaleite layers and unique C3 isosceles triangle rings, is stable over graphite phase above 14.2 GPa. The simulated x-ray diffraction pattern, Raman, and energy-loss near-edge spectrum can match the experimental results very well, indicating that HR-carbon is a likely candidate structure for n-diamond. HR-carbon has an incompressible atomic arrangement because of unique C3 isosceles triangle rings. The hardness and bulk modulus of HR-carbon are calculated to be 80 GPa and 427 GPa, respectively, which are comparable to those of diamond. C3 isosceles triangle rings are very important for the stability and hardness of HR-carbon.

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“…Literature reports indicate that many diamond nanocrystals are structurally inhomogeneous, consisting of ordinary cubic (c-) diamond (space group: Fd-3m), plus several poorly characterized sp 3 -bonded forms, variously called polymorphs, allotropes, or polytypes 8 9 10 11 12 13 14 15 16 17 18 . For uniformity, we call these polymorphs.…”

mentioning

confidence: 99%

“…As such, the structures and characteristics of the reported polymorphs are either controversial or not diagnostic ( Table 1 ). In particular, the existence of h-diamond was recently questioned 19 , and several structural and chemical models were proposed for i-, m-, and n-diamond, including substitution of carbon by hydrogen 9 13 40 and incompletely described diamond forms 41 . Recently, Li et al .…”

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confidence: 99%

Twinning of cubic diamond explains reported nanodiamond polymorphs

Németh

Garvie

Buseck

2015

Sci Rep

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The unusual physical properties and formation conditions attributed to h-, i-, m-, and n-nanodiamond polymorphs has resulted in their receiving much attention in the materials and planetary science literature. Their identification is based on diffraction features that are absent in ordinary cubic (c-) diamond (space group: Fd-3m). We show, using ultra-high-resolution transmission electron microscope (HRTEM) images of natural and synthetic nanodiamonds, that the diffraction features attributed to the reported polymorphs are consistent with c-diamond containing abundant defects. Combinations of {113} reflection and <011> rotation twins produce HRTEM images and d-spacings that match those attributed to h-, i-, and m-diamond. The diagnostic features of n-diamond in TEM images can arise from thickness effects of c-diamonds. Our data and interpretations strongly suggest that the reported nanodiamond polymorphs are in fact twinned c-diamond. We also report a new type of twin (<11> rotational), which can give rise to grains with dodecagonal symmetry. Our results show that twins are widespread in diamond nanocrystals. A high density of twins could strongly influence their applications.

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A new hard allotropic form of carbon: Dream or reality?

Cited by 26 publications

References 22 publications

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Ab initio structure determination of n-diamond

Twinning of cubic diamond explains reported nanodiamond polymorphs

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