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Johari, G. P., Andersson, O. & Sundqvist, B. (2018). Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene. Journal of Chemical Physics, 148(14), Article ID 144502.
Open this publication in new window or tab >>Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene
2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 14, article id 144502Article in journal (Refereed) Published
Abstract [en]

We report on the temperature, pressure and time (T, p and t)- dependent features of thermal conductivity, k, of partially ordered, non-equilibrium state of C60-OG, the orientational glass of Buckminsterfullerene (at T below the orientational freezing temperature Tog) made more unstable (i) by partially depressurizing its high-p formed state to elastically expand it, and (ii) by further pressurizing that state to elastically contract it. The sub-Tog effects observed on heating of C60-OG differ from those of glasses, because phonon propagation depends on the ratio of two well-defined orientational states of C60 molecules and the density of the solid. A broad peak-like feature appears at T near Tog in the k-T plots of C60-OG formed at 0.7 and heated at 0.2 GPa, which we attribute to partial overlap of the sub-Tog and Tog features. A sub-Tog local minimum appears in the k -T plots at T well below Tog  of C60-OG formed at 0.1 GPa and heated at 0.5 GPa, and corresponds to the state of maximum disorder. Although Buckminsterfullerene is regarded as an orientationally-disordered crystal, variation of its properties with T and p is qualitatively different from other such crystals. We discuss the findings in terms of the nature of its disorder, sensitivity of its rotational dynamics to temperature and the absence of the Johari-Goldstein relaxation. All seem to affect the phenomenology of its glass-like transition.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
Keywords
C60, pressure densified glasses, high-pressure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-147236 (URN)10.1063/1.5019832 (DOI)000430128600028 ()29655324 (PubMedID)
Available from: 2018-04-27 Created: 2018-04-27 Last updated: 2018-06-09Bibliographically approved
Du, M., Yao, M., Dong, J., Ge, P., Dong, Q., Kováts, É., . . . Liu, B. (2018). New ordered structure of amorphous carbon clusters induced by fullerene-cubane reactions. Advanced Materials, 30, Article ID 1706916.
Open this publication in new window or tab >>New ordered structure of amorphous carbon clusters induced by fullerene-cubane reactions
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2018 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, article id 1706916Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
ordered amorphous carbon clusters, crystalline structure, high pressures, cubanes, fullerenes, X-ray diffraction, Raman scattering, Raman spectroscopy, rotor–stator compounds
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-147645 (URN)10.1002/adma.201706916 (DOI)000434034100011 ()2-s2.0-85045382980 (Scopus ID)
Available from: 2018-05-11 Created: 2018-05-11 Last updated: 2018-10-01Bibliographically approved
Sundqvist, B. & Tolpygo, V. K. (2018). Saturation and pressure effects on the resistivity of titanium and two Ti-Al alloys. Journal of Physics and Chemistry of Solids, 122, 41-50
Open this publication in new window or tab >>Saturation and pressure effects on the resistivity of titanium and two Ti-Al alloys
2018 (English)In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 122, p. 41-50Article in journal (Refereed) Published
Abstract [en]

The electrical resistivities of a phase titanium and two Ti-Al alloys have been measured as functions of temperature, T, between 4 and 700 K and, in the range 175 to 700 K, as a function of pressure up to 1.2 GPa. All materials showed resistivity saturation effects at the highest temperatures. A “parallel resistivity” saturation model could be fitted to all data with excellent results if Mott-Fermi smearing, expected for a transition metal, was included by adding a term in T3 to the phonon-induced resistivity. However, in the standard saturation model the fitted resistivity parameters were not always realistic. A modified saturation model which partially retained Matthiessen’s rule could be fitted equally well and gave numerically acceptable results for both residual, electron-phonon and saturation resistivities. This new model also fitted the T dependence of the pressure coefficients with a single set of coefficients, each valid for all three materials. Although simple free-electron and Debye models could apparently explain the observed pressure dependence of the impurity and electron-phonon resistivities, a model taking band structure changes with pressure into account showed that the electron-phonon interaction factor of titanium is practically independent of pressure while the plasma frequency has a strong pressure dependence. This model gave reasonable numerical results for the pressure dependence of both the residual, electron-phonon and saturation resistivities and also agreed with experimental data for the superconducting critical temperature Tc under pressure for a titanium.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Electronic transport, Resistivity saturation, High pressure, Electron-phonon coupling, Titanium
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-149618 (URN)10.1016/j.jpcs.2018.05.046 (DOI)000440881800007 ()2-s2.0-85048544043 (Scopus ID)
Funder
Swedish Institute
Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2018-09-13Bibliographically approved
Yang, Z., Hu, K., Meng, X., Tao, Q., Dong, J., Liu, B., . . . Liu, B. b. (2018). Tuning the band gap and the nitrogen content in carbon nitride materials by high temperature treatment at high pressure. Carbon, 130, 170-177
Open this publication in new window or tab >>Tuning the band gap and the nitrogen content in carbon nitride materials by high temperature treatment at high pressure
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2018 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 130, p. 170-177Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Carbon nitride, high pressure, nitrogen stoichiometry, band gap, XPS, Raman scattering, X-ray diffraction
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-143916 (URN)10.1016/j.carbon.2017.12.115 (DOI)000424889200020 ()2-s2.0-85043384118 (Scopus ID)
Note

Supplementary information available at the journal website.

Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-06-18Bibliographically approved
Du, M., Zhou, M., Yao, M., Ge, P., Chen, S., Yang, X., . . . Liu, B. (2017). High pressure infrared spectroscopy study on C60*CS2 solvates. Chemical Physics Letters, 669, 49-53
Open this publication in new window or tab >>High pressure infrared spectroscopy study on C60*CS2 solvates
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2017 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 669, p. 49-53Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
High pressure, IR spectra, Fullerene, C-60*CS2 solvates
National Category
Physical Chemistry Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-132131 (URN)10.1016/j.cplett.2016.11.047 (DOI)000392774900008 ()
Note

Supplementary information available at the journal's website.

Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2018-06-09Bibliographically approved
Sundqvist, B. (2017). Intermolecular bonding in C70 at high pressure and temperature. Carbon, 125, 258-268
Open this publication in new window or tab >>Intermolecular bonding in C70 at high pressure and temperature
2017 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 125, p. 258-268Article in journal (Refereed) Published
Abstract [en]

Near-infrared (NIR) Raman spectroscopy has been used to analyze intermolecular bonding in solid C70, treated for two hours under pressures in the range 0.8 to 2 GPa at temperatures between 350 and 600 K. The spectra obtained are analyzed in detail with the aim of finding spectral lines characteristic for the monomer C70, the dimer C140, and possibly for higher oligomers. In agreement with earlier studies, several new modes are observed in the NIR Raman spectra, in sharp contrast to what is found in Raman studies using visible light excitation. From the relative intensities of the characteristic dimer stretch line at 88 cm-1 and a mode at 457 cm-1, characteristic for the monomer, a semi-quantitative estimate for the dimer fraction in the material can be found as a function of pressure and temperature. From these results a reaction map, similar to that recently derived for C60, can be drawn. The data obtained indicate that C70 is almost completely polymerized into large, random oligomers (or polymers) after long-time treatment at elevated temperatures (> 500 K) and pressures (>1.2 GPa). The phase diagram of C70 is updated and briefly discussed in the light of this and other recent high pressure studies.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fullerenes, C70, high pressure, high temperature, dimer, polymer, intermolecular bond, Raman spectroscopy
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-141430 (URN)10.1016/j.carbon.2017.09.069 (DOI)000413303500028 ()
Note

Supplementary information available at the journal website

Available from: 2017-11-03 Created: 2017-11-03 Last updated: 2018-06-09Bibliographically approved
Yang, X., Yao, M., Wu, X., Liu, S., Chen, S., Yang, K., . . . Liu, B. (2017). Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods. Physical Review Letters, 118(24), Article ID 245701.
Open this publication in new window or tab >>Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods
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2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, no 24, article id 245701Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society, 2017
Keywords
Carbon, Nanotubes, fullerenes, high pressure, superhard material, carbon allotropes, sp3 bonding, X-ray diffraction, hardness, compressibility
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-136919 (URN)10.1103/PhysRevLett.118.245701 (DOI)000403341900005 ()
Available from: 2017-06-26 Created: 2017-06-26 Last updated: 2018-09-28Bibliographically approved
Cui, W., Sun, S., Sundqvist, B., Wang, S. & Liu, B. (2017). Pressure induced metastable polymerization in doped C60 materials. Carbon, 115, 740-745
Open this publication in new window or tab >>Pressure induced metastable polymerization in doped C60 materials
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2017 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 115, p. 740-745Article in journal (Refereed) Published
Abstract [en]

High pressure Raman studies have been carried out on C60/AgNO3 and C60/Ni(OEP) up to 30 GPa. In both these doped C60 materials, pressure-induced metastable ordered polymers can be observed after pressure release. The results show that both the quenched materials contain chainlike polymers and dimers. We also find that the degree of polymerization is higher in these doped C60 materials than in bulk C60 materials after similar high pressure treatment and that C60/AgNO3 contains a higher fraction of chainlike polymers than C60/Ni(OEP) after decompression from same pressure. The results can be understood by considering the different initial lattice structures of these materials and the confinement effects of the dopants.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fullerenes, C60, high pressure, solvate, dimer, polymerization, Raman spectroscopy
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
urn:nbn:se:umu:diva-133631 (URN)10.1016/j.carbon.2017.01.067 (DOI)000395601300081 ()
Note

Supplementary information available at the journal website.

Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-06-09Bibliographically approved
Pei, C., Feng, M., Yang, Z., Yao, M., Yuan, Y., Li, X., . . . Wang, L. (2017). Quasi 3D polymerization in C60 bilayers in a fullerene solvate. Carbon, 124, 499-505
Open this publication in new window or tab >>Quasi 3D polymerization in C60 bilayers in a fullerene solvate
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2017 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 124, p. 499-505Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fullerenes, C60, high pressure, high temperature, polymerization, 3D polymer, intermolecular bonds, Raman scattering, Raman spectroscopy, infra-red spectroscopy, IR spectroscopy, X-ray diffraction
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-141429 (URN)10.1016/j.carbon.2017.09.010 (DOI)000412118200054 ()
Available from: 2017-11-03 Created: 2017-11-03 Last updated: 2018-06-09Bibliographically approved
Sundqvist, B. (2017). Raman identification of C70 monomers and dimers. Paper presented at 10th International Conference on New Diamond & Nano Carbons, 2016 (NDNC 2016), Xi’an, China 2016. Diamond and related materials, 73, 143-147
Open this publication in new window or tab >>Raman identification of C70 monomers and dimers
2017 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 73, p. 143-147Article in journal (Refereed) Published
Abstract [en]

Fullerenes easily polymerize under high pressure by forming covalent intermolecular bonds. For C60 this reaction is easily monitored by Raman scattering, but for C70 no simple method to determine its bonding state is known. In this work C70 has been heated over a wide range of temperatures at a pressure of 1.6 GPa and the treated material has been studied by Raman spectroscopy, using 830 nm laser excitation to avoid photo-induced polymerization. By comparing the present data with earlier results for pure dimers, zig-zag chain polymers and pressure treated powders, characteristic fingerprint peaks can be found for the C70 monomer and the C140 dimer. The molecular stretching mode near 88 cm-1 is a clear fingerprint for dimers while the strong A1′ peak near 455 cm-1 clearly shows the presence of monomers. Several other new peaks appear in pressure-treated material and the relative intensities of many peaks change in a systematic way, but it is not clear whether these changes indicate the presence of dimers or of small oligomers in general. Simple strategies for semi-quantitative structural analysis of pressure-treated C70 material by Raman spectroscopy are briefly discussed.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fullerenes, C70, dimer, polymer, Raman scattering, Raman spectrum, high pressure, high temperature, lattice structure, intermolecular bonding, dimer stretch mode
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-133041 (URN)10.1016/j.diamond.2016.09.001 (DOI)000399519100023 ()
Conference
10th International Conference on New Diamond & Nano Carbons, 2016 (NDNC 2016), Xi’an, China 2016
Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2018-06-09Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0462-6206

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