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Träfflista för sökning "WFRF:(Sundqvist Bertil) ;pers:(Blank Vladimir D.);pers:(Buga Sergei G.)"

Sökning: WFRF:(Sundqvist Bertil) > Blank Vladimir D. > Buga Sergei G.

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1.
  • Blank, Vladimir D., et al. (författare)
  • Electric resistivity and  magnetoresistance of some superhard and ultrahard fullerites in the range 300-2K
  • 1999
  • Ingår i: AIP Conference Proceedings vol. 486 : Electronic Properties of Novel materials - Science and Technology of Molecular Nanostructures: Proceedings of the XIII Winter School on Electronic Properties of Novel Materials, Kirchberg 1999. - Melville, NY : American Institute of Physics (AIP). - 1-56396-900-9 ; s. 416-420
  • Konferensbidrag (refereegranskat)abstract
    • Electric resistivity and magnetoresistance were measured on samples with disordered structure synthesized from pure C60 and C70 at pressures in the range 8 - 12.5 GPa and temperature 900 - 1500 K. Different type of behaviour were observed: semimetallic and semiconducting, depending on the particular short-range order of the structure.
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2.
  • Buga, Sergei G., et al. (författare)
  • Dissociation energy of 3D-polymeric C60 : Calorimetric study and structural analysis
  • 2001
  • Ingår i: Electronic Properties of Novel Materials - Science and Technology of Molecular Nanostructures : Proceedings of the XV International Winter School on Electronic Properties of Novel Materials, Kirchberg 2001. - Melville, NY : American Institute of Physics. - 0-7354-0033-4 ; s. 49-53
  • Konferensbidrag (refereegranskat)abstract
    • Annealing of 2D- and 3D-polymeric C[sub60] fullerene obtained under pressures of 9.5 and 12.5 GPa and temperatures of 670 and 770 K has been investigated by DSC in the range 240–640 K. An endothermal heat effect was observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks.
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3.
  • Buga, Sergei G., et al. (författare)
  • DSC study of annealing and phase transformations of C60 and C70 polymerized under pressures in the range 9.5 - 13 GPa.
  • 2002
  • Ingår i: Journal of Physics and Chemistry of Solids. - Elsevier B.V.. - 0022-3697. ; 63:2, s. 331-343
  • Tidskriftsartikel (refereegranskat)abstract
    • C60 and C70 fullerenes polymerized under pressures between 9.5 and 13 GPa and temperatures between 670 and 1850 K were investigated by differential scanning calorimetry (DSC) in the range 240–640 K. Endothermal heat effects were observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks.
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4.
  • Buga, Sergei G., et al. (författare)
  • Electrical properties of 3D-polymeric crystalline and disordered C60 and C70 fullerites.
  • 2005
  • Ingår i: Diamond and Related Materials vol. 14, special Issue (3-7) : Proceedings of Diamond'04, 15th European Conference on Diamond and Diamond-Like Materials, Riva del Garda, Italy 2004.. - Elsevier B.V.. ; s. 896-901
  • Konferensbidrag (refereegranskat)abstract
    • Crystalline and disordered 3D-polymeric C60 and C70 with different lattice parameters and with densities in the range of 2.2÷3.25 g cm−1 were obtained by high-pressure-high-temperature treatment at P=11.5÷15 GPa, T=670÷1800 K. Their d.c. electrical conductivity was investigated at temperatures 30÷350 K. The variable range hopping mechanism dominates in all samples up to room temperature. A temperature activated conductivity via delocalized states was observed at T>160÷260 K in crystalline C60 samples and in some samples with disordered structure. The evaluated band gap value is Eg=0.28÷0.54 eV for different crystalline structures and 0.06÷0.25 eV for disordered ones
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5.
  • Buga, Sergei G., et al. (författare)
  • Pressure effect on electrical properties and photoluminescence spectra of solid C60 and C70 fullerenes
  • 2001
  • Ingår i: Frontiers of High Pressure Research II: Application of High Pressure to Low-Dimensional Novel Electronic Materials : Proceedings of the NATO Advanced Research Workshop, Pingree Park, CO, USA, from 10-15 June 2001. - Dordrecht : Springer/Kluwer. - 978-1-4020-0160-4 ; s. 483-491
  • Konferensbidrag (refereegranskat)abstract
    • Electrical resistivity of crystalline and disordered fullerite samples obtained by static high-pressure-high-temperature treatment of C-60 and C-70 at P = 12.5 GPa and T = 820-1500 K was investigated in the temperature range of 2.4-300 K, Room-temperature activation energy of charge carriers was found to be in the range 40-200 meV. T-3/2 and T-4 dependencies of conductivity versus temperature were revealed both in crystalline and disordered structures. Photoluminescence spectra of C-60 samples treated at P = 13 GPa. T = 770-1470 K show 50 nm short-wave length shift of characteristic 750 nm PL band.
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6.
  • Buga, Sergei G., et al. (författare)
  • Semimetallic and semiconductor properties of some superhard and ultrahard fullerites in the range 300-2 K
  • 2000
  • Ingår i: Proceedings of the 5th IUMRS International Conference on Advanced Materials, Beijing 1999. - Elsevier B.V.. ; s. 1009-1015
  • Konferensbidrag (refereegranskat)abstract
    • Electrical resistivity and magnetoresistance were measured on samples with disordered structures synthesized from pure C60 and C70 at pressures in the range 8–12.5 GPa and temperatures of 900–1500 K. Different types of behaviour were observed: semimetallic, VRH and semiconducting, depending on the degree of disorder and the particular short-range order of the samples. A negative magnetoresistance was observed at T<10 K on samples with a semimetallic type of conductivity synthesized at 8 GPa pressure. The temperature dependence of resistivity in the sample with a disordered crystalline structure based on 3D-polymerized C60 molecules fits Mott's law for hopping conductivity. T3/2, T2 and T4 dependencies of conductivity are observed for samples with densities of 2.8 and 3.05 g/cm3 synthesized at a pressure of 12.5 GPa. The effect of hydrostatic pressure on the resistivity of cross-linked layered carbon structures obtained from C60 at P=8 GPa, T=1600 K was investigated up to 0.6 GPa at room temperature. An approximately linear decrease of resistivity was observed with a very small value of the derivative d ln ρ/dp=0.06 /GPa, which correlates with a very low compressibility of the material.
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7.
  • Buga, Sergei G., et al. (författare)
  • Synthesis of superhard 3D-polymeric C60 fullerites from rhombohedral 2D-polymer by high-pressure-high-temperature treatment.
  • 2003
  • Ingår i: High Pressure Research vol. 23, issue 3 : Proceedings of the 40th European High Pressure Research Group Meeting on Advances in High Pressure Research (EHPRG'40). - London : Taylor & Francis. ; s. 259-264
  • Konferensbidrag (refereegranskat)abstract
    • Rhombohedral C60 polymer was subjected to high-pressure-high-temperature treatment at P =13 GPa, T =620-1620 K. After quenching, crystalline and disordered structures with densities in the range of 2.1-2.9 g cm-1 were obtained. The structures of the samples have been investigated by powder X-ray diffraction and Raman scattering. DSC analysis showed a transformation of the polymeric structure into monomeric on annealing in the range 400-640 K. The temperature dependence of the electrical resistance of samples with disordered structure was measured in the range 2.5-300K. For different samples, the conductivity was proportional to T1/2, T3/2, T4 and exp(-1/T1/4).
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