On the n-diamond and i-carbon nanocrystalline forms

Abstract

We report on a comparison of the diffraction pattern observed for nanocrystalline n-diamond and i-carbon forms by other investigative teams, with the calculated diffraction pattern of glitter based upon lattice parameters optimized using the DFT-CASTEP method. The close fit of the latter dataset to that observed for ndiamond and i-carbon, as reported herein, suggests that indeed i-carbon may be of the same structure as n-diamond, and that they both may have the tetragonal glitter structure.Keywords Nanocrystalline n-diamond · i-Carbon · DFT-CASTEP method · Tetragonal glitter structure In the carbon science literature, there have been various reports over the previous few decades of potentially novel crystalline forms of carbon emerging as kinetically stabilized, nanometer scale fragments recovered from the explosive remnants of heated, shock compressed graphite and other precursors of C by rapid cooling. Two nanometer-sized and crystalline forms of C that are particularly prominent in these studies are the so-called n-diamond and i-carbon forms [1][2][3][4][5][6][7][8]. Figure 1 below, thus shows a high resolution electron micrograph (HREM) of a representative nanocrystalline C droplet of n-diamond synthesized by such shock methods, where the indexation of the lattice image is to a diamond model [1][2][3][4][5][6][7][8].

Twinning of cubic diamond explains reported nanodiamond polymorphs

“…The synthetic samples were produced through chemical vapor deposition (CVD), and the natural ones were obtained from primitive (Murchison and Orgueil) and impact-shocked (Gujba) meteorites 42 . Samples of similar origins reportedly contain various diamond polymorphs 9 10 11 12 13 16 25 27 .…”

“…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.…”

Homo Citans and Carbon Allotropes: For an Ethics of Citation

“…It was in fact the unit cell of tfi, the structure shown above as 5,called T6 in the PNAS paper and glitter by Roald Hoffmann and Michael Bucknum; [35] the latter has published further on this and related nets. [111][112][113][114] They examined T6 and calculated its electronic structure,i ts phonons,a nd its stability.I n as maller part of the paper, another lattice,r elated to 5,w as examined. Our original paper of 1994 also computed the electronic structure of this hypothetical carbon allotrope, which contains both 3-and 4-connected carbons, [115] which are generally called sp 2 and sp 3 carbon atoms.…”

Structure of Carbon Materials Explored by Local Transmission Electron Microscopy and Global Powder Diffraction Probes

“…Finally, it is worth mentioning recent achievements of ultra-high-resolution TEM in revealing the structure of nanodiamonds. Many powder XRD and ED reports indicated that diamond nanocrystals are structurally inhomogeneous, consisting of cubic (c-) diamond, plus several poorly characterized sp 3 -bonded forms, called polymorphs, or polytypes [154][155][156][157][158][159]. Based on those studies it was suggested that the postulated nanodiamond polymorphs cause the appearance of additional diffraction peaks, in addition to c-diamond reflections.…”