A Revisited Mechanism of the Graphite-to-Diamond Transition at High Temperature

Zhu, Shengcai; Yan, Xiaozhi; Liu, Jin; Oganov, Artem R.; Zhu, Qiang

doi:10.1016/j.matt.2020.05.013

Cited by 52 publications

(42 citation statements)

References 55 publications

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“…Figure 2a is a bright eld (BF) STEM image from a sample recovered from 15 GPa and 1200 °C, in which diamond (D) and graphite (G) nanodomains are clearly distinguished. In neighboring diamond and graphite domains, the lattice fringes of the two phases are tilted relative to one another, forming interfaces different from the (113) CD or (111) CD types as previously proposed for meteoritic or laboratory-shocked diamonds based on TEM observations 4,5,11,14,25 . High-resolution HAADF-STEM observations further con rm the tightly bonded graphitic and diamond domains (Fig.…”

Section: Main Textmentioning

confidence: 81%

“…The transformation from graphite to diamond can be made under different synthetic conditions, such as high pressure high temperature (HPHT) with 6 or without catalyst 7,8 , explosive shock 9 , and even low-temperature compression under severe shear deformation 10 . Along with these experimental efforts, understanding the transformation from graphite to diamond has attracted broad attention but remained a signi cant challenge 11 .…”

Section: Main Textmentioning

confidence: 99%

“…Some reports, again largely based on diffraction, suggested that formation of HD is energetically favored at lower synthesis temperatures 12 . This prompted nucleation-and-growth models 3,13 with two types of transient heterophase junctions proposed between diamond nuclei and graphite matrix 11,14 : One is a graphite-diamond diphase connected with weak van der Waals interaction, the other is covalently bonded interfaces between diamond and graphitic domains with a reduced interlayer distance less than 2.5 angstrom. Similar to the nucleation-and-growth mechanisms, a wave-like lattice buckling and slipping model suggested a stacking order change from AB to ABC by bending graphitic layers, followed by formation of transient heterophase junctions to complete the transformation to CD 15 .…”

Section: Main Textmentioning

confidence: 99%

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Coherent interfaces with mixed hybridization govern direct transformation from graphite to diamond

Zhao

Luo

Liu

et al. 2021

Preprint

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Understanding the direct transformation from graphite to diamond has been a long-standing challenge with great scientific and practical importance. Previously proposed transformation mechanisms1-3, based on traditional experimental observations that lacked atomistic resolution, cannot account for the complex nanostructures occurring at graphite-diamond interfaces during the transformation4,5. Here, we report the identification of coherent graphite-diamond interfaces constituted with four structural motifs in partially transformed graphite samples recovered from static compression, using high-angle annular dark-field scanning transmission electron microscope. These observations provide vital insight into possible pathways of the transformation. Theoretical calculations confirm that transformation through these coherent interfaces is energetically favored to those through other paths previously proposed1-3. The graphite-to-diamond transformation is governed by the formation of nanoscale coherent interfaces (diamond nucleation), which, under static compression, advance to consume the remaining graphite (diamond growth). These results also shed light on transformation mechanisms of other carbon materials and boron nitride under different synthetic conditions.

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Section: Main Textmentioning

confidence: 81%

Section: Main Textmentioning

confidence: 99%

Section: Main Textmentioning

confidence: 99%

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Coherent interfaces with mixed hybridization govern direct transformation from graphite to diamond

Zhao

Luo

Liu

et al. 2021

Preprint

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show abstract

“…Moreover, despite we observed small amount of CD, the transformation pathway HGàOGàHD is more energetically favorable than HGàOGàCD at mild HPHT conditions. Recent experimental results 33 showed the successful synthesis of single-phase HD crystal recovered from HPHT, further indicating that CD nucleation is suppressed under these synthesis conditions and HD exists as a discrete material rather than just a faulted or twined diamond 36,37 . In addition, HD is predicted to 58% harder than CD 38 .…”

Section: Discussionmentioning

confidence: 99%

Atomistic Evidence of Nucleation Mechanism for the Direct Graphite-to-Diamond Transformation

Luo

Yang

Xie

et al. 2021

Preprint

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The direct graphite-to-diamond transformation mechanism has been a subject of intense study and remains debated concerning the initial stages of the conversion, the intermediate phases, and their transformation pathways. Here, we successfully recover samples at early conversion stage by tuning high-pressure/high-temperature conditions and reveal direct evidence supporting the nucleation-growth mechanism. Atomistic observations show that intermediate orthorhombic graphite phase mediates the growth of diamond nuclei. Furthermore, we observe that quenchable orthorhombic and rhombohedra graphite are stabilized in buckled graphite at lower temperatures. These intermediate phases are further converted into hexagonal and cubic diamond at higher temperatures following energetically favorable pathways in the order: graphite -> orthorhombic graphite -> hexagonal diamond, graphite -> orthorhombic graphite -> cubic diamond, graphite -> rhombohedra graphite -> cubic diamond. These results significantly improve our understanding of the transformation mechanism, enabling the synthesis of different high-quality forms of diamond from graphite.

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“…Both classical MD 32 and ab initio MD simulations were carried out to study the structure evolution of C60 under high-pressure condition and simulate the formation of p-D. For classical MD, a newly developed angular-dependent interatomic potential (C-ADP) 33,53 was used to describe carbon. The…”

Section: Competing Interestsmentioning

confidence: 99%

Synthesis of Paracrystalline Diamond

Sheng

Tang

Yuan

et al. 2021

Preprint

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Solids in nature can be generally classified into crystalline and non-crystalline states, depending on whether long-range lattice periodicity is present in the material. The differentiation of the two states, however, could face fundamental challenges if the degree of long-range order in crystals is significantly reduced. Here we report a unique paracrystalline state of diamond that is distinct from either crystalline or amorphous diamond. The paracrystalline diamond reported in this work, consisting of sub-nanometer-sized paracrystals that possess a well-defined crystalline medium-range order up to a few atomic shells, was synthesized in high-pressure high-temperature conditions (e.g., 30 GPa, 1600 K) employing fcc-C60 as a precursor. The structural characteristics of paracrystalline diamond was identified through a combination of X-ray diffraction, high-resolution transmission microscopy, and advanced molecular dynamics simulation. The formation of paracrystalline diamond is a result of densely distributed nucleation sites developed in compressed C60 as well as pronounced second-nearest-neighbor short-range order in amorphous diamond due to strong sp3 bonding. The discovery of paracrystalline diamond adds a new diamond form to the enriched carbon family, which exhibits distinguishing physical properties and can be furthered exploited to develop new materials. Furthermore, this work reveals the missing link in the length-scale between amorphous and crystalline states across the structural landscape, which has profound implications for recognizing complex structures arising from amorphous materials.

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A Revisited Mechanism of the Graphite-to-Diamond Transition at High Temperature

Cited by 52 publications

References 55 publications

Coherent interfaces with mixed hybridization govern direct transformation from graphite to diamond

Coherent interfaces with mixed hybridization govern direct transformation from graphite to diamond

Atomistic Evidence of Nucleation Mechanism for the Direct Graphite-to-Diamond Transformation

Synthesis of Paracrystalline Diamond

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