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Dive into the research topics where Bertil Sundqvist is active.

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Featured researches published by Bertil Sundqvist.


Journal of Physical Chemistry Letters | 2012

Phase Transitions in Graphite Oxide Solvates at Temperatures Near Ambient

Shujie You; Serhiy M. Luzan; Junchun Yu; Bertil Sundqvist; Alexandr V. Talyzin

It is demonstrated that solvent-saturated graphite oxide can be considered to be solid solvate, and two phases with distinctly different solvent composition are found near room temperature. Phase transitions between these two solvated phases were observed using synchrotron powder X-ray diffraction and DSC for methanol, ethanol, acetone, and dimethylformamide (DMF) solvents. Solvate A, formed at room temperature, undergoes a reversible phase transition into expanded Solvate L at temperatures slightly below ambient due to insertion of one monolayer of solvent molecules between the GO planes. The phase transition is reversible upon heating, whereas the low-temperature expanded phase L can be quenched to room temperature for ethanol and DMF solvates.


ACS Nano | 2013

Enormous lattice expansion of hummers graphite oxide in alcohols at low temperatures.

Shujie You; Bertil Sundqvist; Alexandr V. Talyzin

A structural study of swelling of Hummers graphite oxide (H-GO) in excess of liquid alcohols was performed as a function of temperature using synchrotron X-ray diffraction and revealed a strong negative thermal expansion effect. The increase of the distance between graphene oxide layers is explained by insertion of additional solvent upon cooling of the H-GO/solvent system. The interlayer distance of H-GO is found to increase gradually upon temperature decrease, reaching 19.4 and 20.6 Å at 140 K for methanol and ethanol, respectively. The gradual expansion of the H-GO lattice upon cooling corresponds to insertion of at least two additional solvent monolayers and can be described as osmotic swelling. This phenomenon is distinctly different from the solvation of Brodie graphite oxide (B-GO), which was found earlier to exhibit crystalline swelling: single-step insertion of an additional solvent monolayer at low temperatures. The enormous structural expansion of H-GO at low temperatures is suggested to be useful for solution-based intercalation of graphite oxide with relatively large molecules and the synthesis of various composite materials.


Applied Physics Letters | 2013

Pressure-induced transformation and superhard phase in fullerenes: The effect of solvent intercalation

Mingguang Yao; Wen Cui; Junping Xiao; Shuanglong Chen; Jinxing Cui; Ran Liu; Tian Cui; Bo Zou; Bingbing Liu; Bertil Sundqvist

We studied the behavior of solvated and desolvated C60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C60s are similar in the two samples, both undergoing deformation and amorphization. Nevertheless, the high pressure phases of solvated C60 can indent diamond anvils while that of desolvated C60s cannot. Further experiments suggest that the solvents in the solvated C60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization.


Low Temperature Physics | 2012

The specific heat and the radial thermal expansion of bundles of single-walled carbon nanotubes

M. I. Bagatskii; M. S. Barabashko; A. V. Dolbin; V. V. Sumarokov; Bertil Sundqvist

The specific heat at constant pressure C(T) of bundles of single-walled carbon nanotubes (SWNTs) closed at their ends has been investigated in the temperature interval of 2–120u2009K. It is found that the curve C(T) has features near 5, 36, 80, and 100u2009K. The experimental results on the C(T) and the radial thermal expansion coefficient αR(T) of bundles of SWNTs oriented perpendicular to the sample axis have been compared. It is found that the curves C(T) and αR(T) exhibit a similar temperature behavior at Tu2009>u200910u2009K. The temperature dependence of the Gruneisen coefficient γ(T) has been calculated. The curve γ(T) also has a feature near 36u2009K. Above 36u2009K the Gruneisen coefficient is practically independent of temperature (γu2009≈u20094). Below 36u2009K, γ(T) decreases monotonically with lowering temperature and becomes negative at Tu2009<u20096u2009K.


Scientific Reports | 2015

Mapping intermolecular bonding in C60

Bertil Sundqvist

The formation of intermolecular bonds in C60 has been investigated in detail at pressures below 2.2u2005GPa and up to 750u2005K. Fullerene samples were heated in a temperature gradient to obtain data on the formation of dimers and low-dimensional polymers along isobars. Intermolecular bonding was analyzed ex situ by Raman scattering, using both intramolecular modes and intermolecular stretching modes. Semi-quantitative reaction maps are given for the formation of dimers and chains. The activation energy for dimer formation decreases by 0.2u2005meV pm−1 when intermolecular distances decrease and dimer formation is noticeably affected by the rotational state of molecules. Above 400–450u2005K larger oligomers are formed; below 1.4u2005GPa most of these are disordered, with small domains of linear chains, but above this the appearance of stretching modes indicates the existence of ordered one-dimensional polymers. At the highest pressures and temperatures two-dimensional polymers are also observed.


Advanced Materials | 2015

Tailoring Building Blocks and Their Boundary Interaction for the Creation of New, Potentially Superhard, Carbon Materials

Mingguang Yao; Wen Cui; Mingrun Du; Junping Xiao; Xigui Yang; Shijie Liu; Ran Liu; Fei Wang; Tian Cui; Bertil Sundqvist; Bingbing Liu

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.


Low Temperature Physics | 2011

Self-heating of metallic carbon nanotube bundles in the regime of the Luttinger-liquid conductivity

B. A. Danilchenko; N. A. Tripachko; E. A. Voytsihovska; I. A. Obukhov; I. I. Yaskovets; Bertil Sundqvist

The conductivity of bundles of carbon single-walled nanotubes with metallic conductivity (metallic nanotubes) is investigated over the wide temperature range 4.2-330 K and electrical fields up to 5 ...


Journal of Physics: Condensed Matter | 2002

Resistivity and fractal structure in carbon nanotube networks

Bingbing Liu; Bertil Sundqvist; Dongmei Li; Guangtian Zou

We have measured the temperature and magnetic field dependence of the resistance for bulk samples of single-walled nanotubes treated in different ways. Hydrostatic pressure-treated samples and as-grown samples show a two-dimensional variable-range hopping behaviour while samples treated in non-hydrostatic pressure or in acid for a long time show a three-dimensional transport behaviour. We suggest that the observed two-dimensional behaviour arises from a network structure with a fractal dimension lower than three.


Physical Review Letters | 2017

Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods

Xigui Yang; Mingguang Yao; Xiangying Wu; Shijie Liu; Shuanglong Chen; Ke Yang; Ran Liu; Tian Cui; Bertil Sundqvist; Bingbing Liu

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 C_{70} peapods, which most likely can be identified with a fully sp^{3}-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 90xa0GPa and a bulk modulus ∼400u2009u2009GPa, 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 100xa0GPa, 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 sp^{3}-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.


Low Temperature Physics | 2015

The low-temperature heat capacity of fullerite C60

M. I. Bagatskii; V. V. Sumarokov; M. S. Barabashko; A. V. Dolbin; Bertil Sundqvist

The heat capacity at constant pressure of fullerite C60 has been investigated using an adiabatic calorimeter in a temperature range from 1.2 to 120u2009K. Our results and literature data have been analyzed in a temperature interval from 0.2 to 300u2009K. The contributions of the intramolecular and lattice vibrations into the heat capacity of C60 have been separated. The contribution of the intramolecular vibration becomes significant above 50u2009K. Below 2.3u2009K the experimental temperature dependence of the heat capacity of C60 is described by the linear and cubic terms. The limiting Debye temperature at T→0 K has been estimated (Θ0u2009=u200984.4u2009K). In the interval from 1.2 to 30u2009K the experimental curve of the heat capacity of C60 describes the contributions of rotational tunnel levels, translational vibrations (in the Debye model with Θ0u2009=u200984.4u2009K), and librations (in the Einstein model with ΘE,libu2009=u200932.5u2009K). It is shown that the experimental temperature dependences of heat capacity and thermal expansion are proportional ...

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