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| 44. |
- Chernogorova, Olga, et al.
(författare)
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Structure and physical properties of nanoclustered graphene synthesized from C-60 fullerene under high pressure and high temperature
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:4
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Tidskriftsartikel (refereegranskat)abstract
- C-60 treatment at 5-8 GPa, similar to 1000 degrees C results in the fullerene cage collapse and transformation to a phase with outstanding mechanical properties. A detailed structural analysis of the phase reveals that it comprised 7-12 layer graphene clusters with lateral dimension of 2-4 nm. Raman spectra of the nanoclustered graphene phase are similar to those of disordered sp(2) carbon structure with an admixture of sp(3)-bonded carbon. The phase is characterized by a high (up to 19 GPa) hardness, relatively low (about 70 GPa) Young modulus and up to 95% elastic recovery, determining excellent wear resistance and good antifriction properties. (C) 2014 AIP Publishing LLC.
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| 45. |
- Ji, Cheng, et al.
(författare)
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Crystallography of low Z material at ultrahigh pressure : Case study on solid hydrogen
- 2020
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Ingår i: Matter and Radiation at Extremes. - : American Institute of Physics (AIP). - 2468-2047 .- 2468-080X. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558–562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen.
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| 47. |
- Lange, Kathrin M., et al.
(författare)
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On the Origin of the Hydrogen-Bond-Network Nature of Water : X-Ray Absorption and Emission Spectra of Water-Acetonitrile Mixtures
- 2011
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 50:45, s. 10621-10625
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Tidskriftsartikel (refereegranskat)abstract
- A liquid microjet was used to obtain oxygen K-edge X-ray absorption and emission spectra of water–acetonitrile mixtures of various compositions. The observed spectral changes are unambiguously related to the increasing number of broken hydrogen bonds with decreasing water concentration, and the hydrogen-bond network of liquid water can thus be addressed on purely experimental grounds without the need for theoretical modeling.
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| 48. |
- Mases, Mattias, et al.
(författare)
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In situ electrical conductivity and Raman study of C60 tetragonal polymerat high pressures up to 30 GPa
- 2010
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 274:11/12, s. 3068-3071
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts that tetragonal polymeric C60 will undergo a phase transition into a metallic phase at pressures around 20 GPa. Raman and structural experiments at high pressures confirmed formation of a new phase above 20 GPa although the question about its electrical properties was still open. We report on the first simultaneous in situ study of vibrational and electrical properties of two-dimensional (2D) tetragonal C60 polymer at pressures up to 30 GPa in a diamond anvil cell (DAC) specially designed for this purpose. Our results reveal an anomaly in Raman spectra and a drop in electrical resistance of the sample at 20-25 GPa. We tentatively associate this anomalous behaviour with a phase transition into the conductive phase although its metallic character is yet to be proven.At high pressures the Raman spectra exhibit a high degree of disorder. Upon pressure release the order was partially restored and, more importantly, a significant amount of the initial 2D polymeric phase was recovered.
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| 49. |
- Soldatov, Alexander, et al.
(författare)
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Topochemical polymerization of C70 controlled by monomer crystal packing
- 2001
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Ingår i: Science. - : American Association for the Advanement of Science. - 0036-8075 .- 1095-9203. ; 293:5530, s. 680-683
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Tidskriftsartikel (refereegranskat)abstract
- Polymeric forms of C60 are now well known, but numerous attempts to obtain C70 in a polymeric state have yielded only dimers. Polymeric C70 has now been synthesized by treatment of hexagonally packed C70 single crystals under moderate hydrostatic pressure (2 gigapascals) at elevated temperature (300°C), which confirms predictions from our modeling of polymeric structures of C70. Single-crystal x-ray diffraction shows that the molecules are bridged into polymeric zigzag chains that extend along the c axis of the parent structure. Solid-state nuclear magnetic resonance and Raman data provide evidence for covalent chemical bonding between the C70 cages.
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| 50. |
- You, Shujie, et al.
(författare)
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Probing structural stability of double-walled carbon nanotubes at high non-hydrostatic pressure by Raman spectroscopy
- 2011
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 31:1, s. 186-190
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations predict that the collapse pressure for double-walled carbon nanotubes (DWCNTs) is proportional to 1/R3, where R is the effective or average radius of a DWCNT. In order to address the problem of CNT stability at high pressure and stress, we performed a resonance Raman study of DWCNTs dispersed in sodium cholate using 532 and 633 nm laser excitation. Raman spectra of the recovered samples show minor versus irreversible changes with increasing ID/IG ratio after exposure to high non-hydrostatic pressure of 23 and 35 GPa, respectively. The system exhibits nearly 70% pressure hysteresis in radial breathing vibrational mode signals recovery on pressure release which is twice that predicted by theory.
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