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Crystal structure of graphite under room-temperature compression and decompression.

Wang Y, Panzik JE, Kiefer B, Lee KK - Sci Rep (2012)

Bottom Line: Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C(4), H-, M-, R-, S-, W-, and Z-carbon).However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa.Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA. ywang235@oakland.edu

ABSTRACT
Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C(4), H-, M-, R-, S-, W-, and Z-carbon). However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa. Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures. Furthermore, we show that this phase transition is extremely sluggish, which led to the observed broad x-ray diffraction peaks in previous studies and hindered the proper identification of the post-graphite phase in cold-compressed carbon.

No MeSH data available.


Related in: MedlinePlus

Photomicrographs showing the damaged diamond anvils after high-pressure experiments.(a) Photomicrograph of graphite loaded in a DAC at ambient pressure. (b) Minor scratch on the anvil surface by M-carbon after reaching a maximum pressure of 32 GPa. The photo was taken after the experiment with reflected light. (c) Severely damaged anvil surface by M-carbon after reaching a maximum pressure of 50 GPa. The photo was taken after the experiment with transmitted light. All culets are 300 μm in diameter.
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f7: Photomicrographs showing the damaged diamond anvils after high-pressure experiments.(a) Photomicrograph of graphite loaded in a DAC at ambient pressure. (b) Minor scratch on the anvil surface by M-carbon after reaching a maximum pressure of 32 GPa. The photo was taken after the experiment with reflected light. (c) Severely damaged anvil surface by M-carbon after reaching a maximum pressure of 50 GPa. The photo was taken after the experiment with transmitted light. All culets are 300 μm in diameter.

Mentions: Upon releasing pressure to ambient conditions, we observed cracks on the culets of the diamond anvils, which follow the sample boundary in the gasket hole (Fig. 7) similar to anvil damage observed previously5. This observation suggests the presence of a carbon phase with similar mechanical properties to diamond and a similar sp3 carbon bond topology, consistent with most of the predicted high-pressure carbon phases. However, the XRD data (Fig. 3) supports M-carbon as this phase and the damage to the diamond culets provides additional evidence that the mechanical strength of M-carbon rivals that of diamond as estimated previously25. The severity of the anvil's damage depends on the highest pressure achieved during compression. At 32 GPa, only a microcrack emerged on the anvil's surface following the sample's boundary (Fig. 7b). However, at 50 GPa, M-carbon fractured the diamond anvils following the sample's boundary, deforming and indenting the central portion of diamond such that the exertion of highly-concentrated stress on the gasket-diamond contact area lead to severe damage on the outer portion of the culet (Fig. 7c). This is consistent with previous observations of culet damage due to room-temperature compression of graphite5.


Crystal structure of graphite under room-temperature compression and decompression.

Wang Y, Panzik JE, Kiefer B, Lee KK - Sci Rep (2012)

Photomicrographs showing the damaged diamond anvils after high-pressure experiments.(a) Photomicrograph of graphite loaded in a DAC at ambient pressure. (b) Minor scratch on the anvil surface by M-carbon after reaching a maximum pressure of 32 GPa. The photo was taken after the experiment with reflected light. (c) Severely damaged anvil surface by M-carbon after reaching a maximum pressure of 50 GPa. The photo was taken after the experiment with transmitted light. All culets are 300 μm in diameter.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3400081&req=5

f7: Photomicrographs showing the damaged diamond anvils after high-pressure experiments.(a) Photomicrograph of graphite loaded in a DAC at ambient pressure. (b) Minor scratch on the anvil surface by M-carbon after reaching a maximum pressure of 32 GPa. The photo was taken after the experiment with reflected light. (c) Severely damaged anvil surface by M-carbon after reaching a maximum pressure of 50 GPa. The photo was taken after the experiment with transmitted light. All culets are 300 μm in diameter.
Mentions: Upon releasing pressure to ambient conditions, we observed cracks on the culets of the diamond anvils, which follow the sample boundary in the gasket hole (Fig. 7) similar to anvil damage observed previously5. This observation suggests the presence of a carbon phase with similar mechanical properties to diamond and a similar sp3 carbon bond topology, consistent with most of the predicted high-pressure carbon phases. However, the XRD data (Fig. 3) supports M-carbon as this phase and the damage to the diamond culets provides additional evidence that the mechanical strength of M-carbon rivals that of diamond as estimated previously25. The severity of the anvil's damage depends on the highest pressure achieved during compression. At 32 GPa, only a microcrack emerged on the anvil's surface following the sample's boundary (Fig. 7b). However, at 50 GPa, M-carbon fractured the diamond anvils following the sample's boundary, deforming and indenting the central portion of diamond such that the exertion of highly-concentrated stress on the gasket-diamond contact area lead to severe damage on the outer portion of the culet (Fig. 7c). This is consistent with previous observations of culet damage due to room-temperature compression of graphite5.

Bottom Line: Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C(4), H-, M-, R-, S-, W-, and Z-carbon).However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa.Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA. ywang235@oakland.edu

ABSTRACT
Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C(4), H-, M-, R-, S-, W-, and Z-carbon). However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa. Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures. Furthermore, we show that this phase transition is extremely sluggish, which led to the observed broad x-ray diffraction peaks in previous studies and hindered the proper identification of the post-graphite phase in cold-compressed carbon.

No MeSH data available.


Related in: MedlinePlus