Shock-formed carbon materials with intergrown sp ³ - and sp ² -bonded nanostructured units

Abstract

Studies of dense carbon materials formed by bolide impacts or produced by laboratory compression provide key information on the high-pressure behavior of carbon and for identifying and designing unique structures for technological applications. However, a major obstacle to studying and designing these materials is an incomplete understanding of their fundamental structures. Here, we report the remarkable structural diversity of cubic/hexagonally ( c / h ) stacked diamond and their association with diamond-graphite nanocomposites containing sp 3 -/sp 2 -bonding patterns, i.e., diaphites, from hard carbon materials formed by shock impact of graphite in the Canyon Diablo iron meteorite. We show evidence for a range of intergrowth types and nanostructures containing unusually short (0.31 nm) graphene spacings and demonstrate that previously neglected or misinterpreted Raman bands can be associated with diaphite structures. Our study provides a structural understanding of the material known as lonsdaleite, previously described as hexagonal diamond, and extends this understanding to other natural and synthetic ultrahard carbon phases. The unique three-dimensional carbon architectures encountered in shock-formed samples can place constraints on the pressure–temperature conditions experienced during an impact and provide exceptional opportunities to engineer the properties of carbon nanocomposite materials and phase assemblages.

Canyon Diablo lonsdaleite is a nanocomposite containing c/h stacking disordered diamond and diaphite

“…However, the 1.51 Å XRD feature, corresponding to the d spacing of the false(101false¯2false) h diamond, is missing. Synchrotron microbeam XRD maps obtained from 2.0 × 2.0 µm −2 areas of Canyon Diablo hard grains reveal their heterogeneous nanocomposite structure [31]. These patterns are characterized by diffuse and continuous rings.…”

“…The structure of a hard carbon grain was investigated from two FIB thinned lamellae, which were prepared from two areas after rotating the grain by 90° (figure 5 c ). The low-magnification TEM image of lamella 1 reveals a feathery texture (figure 5 c ), which may reflect previous graphitic layering arranged into bundles [31]. The corresponding SAED pattern, taken from an approximately 200 nm size area, is characterized by quasi-continuous rings, of which the strongest intensity can be indexed as falsefalse⟨011false¯falsefalse⟩ c diamond (figure 5 c ).…”

“…( c ) Example structure of c/h stacking disordered diamond projected along falsefalse⟨101false¯0falsefalse⟩. Hexagonal and cubic stacking are indicated by ‘h’ and ‘c’, respectively.

Figure 3Structure model of type 1 and type 2 diaphite structures and their corresponding simulated XRD patterns plotted on XRD data measured from 2.0 × 2.0 µm −2 areas of two Canyon Diablo grains referred to as grain 8 and grain 7 in [31]. ( a ) For type 1 diaphite graphene layers with ‘g+’ and ‘g−’ type stackings are inserted within c/h stacking disordered diamond.

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“…Given the apparent nanometre scale of the diffracting domains, transmission electron microscopy (TEM) has been used to probe the structure of samples that are thought to contain lonsdaleite [24][25][26][27][28][29][30][31]. In particular, selected-area electron diffraction (SAED) patterns and fast Fourier transforms (FFTs) calculated from high-resolution TEM (HRTEM) images have been used to report h diamond (Supplementary Materials in [31]). However, analogous to the XRD patterns, the electron diffraction patterns show broadening and streaking of the diffraction spots.…”

Production of diamond using intense heavy ion beams at the FAIR facility and application to planetary physics

“…Another research area that will benefit from these studies is the investigation of the formation conditions of various stacking disordered carbon structures produced as a result of large asteroidal impacts. For instance, diamond structures called diaphites [5][6][7] , that have been discovered at the impact sites, Canyon Diablo and Popigai. Due to the special electronic and mechanical properties of these diamond forms, they may have high potential industrial significance, that underlines their importance.High pressure experiments suggest that large amount of diamonds are formed from methane on the ice giant planets, Uranus and Neptune.…”