| 1. |
- Cui, Jinxing, et al.
(författare)
-
Structural Deformation of Sm@C88under High Pressure
- 2015
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 5
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the structural transformation of Sm@C88 under pressure up to 18 GPa by infraredspectroscopy combined with theoretical simulations. The infrared-active vibrational modes of Sm@C88 at ambient conditions have been assigned for the first time. Pressure-induced blue and red shiftsof the corresponding vibrational modes indicate an anisotropic deformation of the carbon cage uponcompression. We propose that the carbon cage changes from ellipsoidal to approximately sphericalaround 7 GPa. A smaller deformation of the carbon bonds in the area close to the Sm atom in thecage suggests that the trapped Sm atom plays a role in minimizing the compression of the adjacentbonds. Pressure induced a significant reduction of the band gap of the crystal. The HOMO-LUMOgap of the Sm@C88 molecule decreases remarkably at 7 GPa as the carbon cage is deformed. Also,compression enhances intermolecular interactions and causes a widening of the energy bands. Botheffects decrease the band gap of the sample. The carbon cage deforms significantly above 7 GPa,from spherical to a peanut-like shape and collapses at 18 GPa.
|
|
| 2. |
- Cui, Wen, et al.
(författare)
-
High pressure and high temperature induced polymerization of doped C60 materials
- 2016
-
Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 109, s. 269-275
-
Tidskriftsartikel (refereegranskat)abstract
- Several metastable doped C60 polymers are synthesized under high pressure and high temperature (1.5GPa, 573K and 2GPa, 700K, respectively), using C60/ferrocene (Fc, Fe(C5H5)2), C60/Ni(OEP) and C60/AgNO3 as starting materials. Raman and IR spectroscopy are used to study the polymerization of these samples after HPHT treatment. It is found that the polymerization degree is always lower than that of pure C60 treated at same conditions, which is attributed to the space limitation by the dopants. We also find that even at same conditions, the three doped materials form different polymeric phases of the doped materials. This is attributed to the unique initial lattice structures and the different degrees of spatial confinement provided by the dopants.
|
|
| 3. |
- Du, Mingrun, et al.
(författare)
-
High pressure infrared spectroscopy study on C60*CS2 solvates
- 2017
-
Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 669, s. 49-53
-
Tidskriftsartikel (refereegranskat)abstract
- High pressure IR study has been carried out on C-60*CS2 solvates up to 34.8 GPa. It is found that the intercalated CS2 molecules significantly affect the transformations of C-60 molecules under pressure. As a probe, the intercalated CS2 molecules can well detect the orientational ordering transition and deformation of C-60 molecules under pressure. The chemical stability of CS2 molecules under pressure is also dramatically enhanced due to the spacial shielding effet from C-60 molecules around in the solvated crystal. These results provide new insight into the effect of interactions between intercalants and fullerenes on the transformations in fullerene solvates under pressure.
|
|
| 4. |
- Du, Mingrun, et al.
(författare)
-
New ordered structure of amorphous carbon clusters induced by fullerene-cubane reactions
- 2018
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- As a new category of solids, crystalline materials constructed with amorphous building blocks expand the structure categorization of solids, for which designing such new structures and understanding the corresponding formation mechanisms are fundamentally important. Unlike previous reports, new amorphous carbon clusters constructed ordered carbon phases are found here by compressing C8H8/C60 cocrystals, in which the highly energetic cubane (C8H8) exhibits unusual roles as to the structure formation and transformations under pressure. The significant role of C8H8 is to stabilize the boundary interactions of the highly compressed or collapsed C60 clusters which preserves their long‐range ordered arrangement up to 45 GPa. With increasing time at high pressure, the gradual random bonding between C8H8 and carbon clusters, due to “energy release” of highly compressed cubane, leads to the loss of the ability of C8H8 to stabilize the carbon cluster arrangement. Thus a transition from short‐range disorder to long‐range disorder (amorphization) occurs in the formed material. The spontaneous bonding reconstruction most likely results in a 3D network in the material, which can create ring cracks on diamond anvils.
|
|
| 5. |
- Pei, Cuiying, et al.
(författare)
-
Quasi 3D polymerization in C60 bilayers in a fullerene solvate
- 2017
-
Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 124, s. 499-505
-
Tidskriftsartikel (refereegranskat)abstract
- The polymerization of fullerenes has been an interesting topic for almost three decades. A rich polymeric phase diagram of C60 has been drawn under a variety of pressure-temperature conditions. However, only linear or perpendicular linkages of C60 are found in the ordered phases. Here we used a unique bilayer structural solvate, C60∙1,1,2-trichloroethane (C60∙1TCAN), to generate a novel quasi-3D C60 polymer under high pressure and/or high temperature. Using Raman, IR spectroscopy and X-ray diffraction, we observe that the solvent molecules play a crucial role in confining the [2+2] cycloaddition bonds of C60s forming in the upper and lower layers alternately. The relatively long distance between the two bilayers restricts the covalent linkage extended in a single individual bilayer. Our studies not only enrich the phase diagram of polymeric C60, but also facilitate targeted design and synthesis of unique C60 polymers.
|
|
| 6. |
- Sundqvist, Bertil, et al.
(författare)
-
AC impedance of A4C60 fullerides under pressure
- 2015
-
Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 17:2
-
Tidskriftsartikel (refereegranskat)abstract
- Three A4C60 compounds, with A = Li, Na and K, have been studied by impedance spectroscopy between 100 K and 293 K at pressures up to 2 GPa. The results are in very good agreement with earlier DC resistance studies and with data from the literature. For all three materials the measured conductivity can be fitted by a sum of at least two Arrhenius terms. The band gaps derived from the resistance data, 0.3 eV for Na4C60 and 0.5 eV for K4C60, are in excellent agreement with data measured by other methods. For Li4C60, our results disagree with a recent suggestion that the conductivity is dominated by ionic conduction. Although a certain ionic component probably exists we suggest that electronic transport dominates in our samples at and below room temperature because the derived “activation energy” decreases under pressure, the derived “activation volume” is negative, and we observe neither a significant electrode blocking capacitance nor any significant metal transport under DC conditions.
|
|
| 7. |
- Yang, Xigui, et al.
(författare)
-
Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods
- 2017
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 118:24
-
Tidskriftsartikel (refereegranskat)abstract
- Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed C70 peapods, which most likely can be identified with a fully sp3-bonded monoclinic structure, here named V carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near K-edge spectroscopy, and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ∼400 GPa, which well explains the "ring crack" left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp3-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.
|
|
| 8. |
- Yang, Xigui, et al.
(författare)
-
Polarized Raman study of aligned multiwalled carbon nanotubes arrays under high pressure
- 2015
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:49, s. 27759-27767
-
Tidskriftsartikel (refereegranskat)abstract
- Tuning the intertube interaction and the topological structure of carbon nanotubes by the application of pressure may obviously affect their properties such as optical and electronic properties. However, characterizing such changes is still challenging. Here, we performed polarized Raman scattering studies on aligned multiwalled carbon nanotube arrays (MWNTAs). Unlike researchers from the previous literature, we found that the MWNTAs exhibit a polarization dependence similar to that of isolated single walled carbon nanotubes at ambient conditions. Upon compression, the polarization dependence weakens gradually with increasing pressure up to ∼20 GPa, which has been discussed in terms of pressure-induced enhancement of intertube interactions. At around 20 GPa, the depolarization effect vanishes, which can be explained by the formation of interlinked sp3 bonding in the MWNTAs. Our results show that polarized Raman spectroscopy is an efficient method to explore not only intertube interaction but also structural transition changes in MWNTs, which overcome the difficulty that MWNTs have no obvious fingerprints like those of single-walled carbon nanotubes in the study of structural transformations.
|
|
| 9. |
- Yang, Zhenxing, et al.
(författare)
-
Tuning the band gap and the nitrogen content in carbon nitride materials by high temperature treatment at high pressure
- 2018
-
Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 130, s. 170-177
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride (C-N) materials have been attracting great interest because of their extraordinary performance in photocatalysis and energy conversion. However, developing an effective strategy for achieving band-gap engineering of C-N materials to satisfy practical applications remains highly desired. Here we report an efficient way to tune the band gap and control the nitrogen stoichiometry in carbon nitride compounds by using high pressure and high temperature (HPHT) treatment. It is found that treating a g-C3N4 precursor at relatively low temperature (630oC and below) under pressure can efficiently narrow the band gap even down to the red light region (~600 nm), increase the crystallinity, and significantly improve the charge carrier separation efficiency (by two orders of magnitude), almost without changing their stoichiometry. When increasing the treatment temperature under pressure, nitrogen-doped graphene/graphite materials with weak ferromagnetism were obtained. We thus obtained C-N materials with tunable band gaps, ranging from semiconducting to metallic states. XPS measurements show that pyridinic nitrogen is preferentially eliminated under such HPHT conditions while graphitic nitrogen is preserved in the C-N network. Our results thus provide an efficient strategy for tuning the structure and physical properties of C-N materials for applications.
|
|
| 10. |
- Yao, Mingguang, et al.
(författare)
-
Tailoring Building Blocks and Their Boundary Interactionfor the Creation of New, Potentially Superhard, Carbon Materials
- 2015
-
Ingår i: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 27:26, s. 3962-3968
-
Tidskriftsartikel (refereegranskat)abstract
- A strategy for preparing hybrid carbon structures with amorphous carbon clusters as hard building blocks by compressing a series of predesigned two-component fullerides is presented. In such constructed structures the building blocks and their boundaries can be tuned by changing the starting components, providing a way for the creation of new hard/superhard materials with desirable properties.
|
|
