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Spectroscopy of carbon materials under high pressure

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					                              Spectroscopy of carbon materials under high pressure
        The study of phase transitions under high pressure (HP) in carbon-based materials is an important trend in
the Laboratory. These investigations are carried out jointly with Technological Institute for Superhard and Novel
Carbon Materials (Prof. V.D. Blank). Two techniques of optical investigations of carbon materials are developed:
                                                           - in situ HP using diamond anvil cell with shear
                                                   deformation (DACS)up to 110 GPa (Fig. 1),
                                                           - after HPHT treatment in bulk toroid-type apparatus up to
                                                   15 GPa and 2100 K.
                                                   Fig. 15. Diamond anvil cell: 1 – diamond anvils, 2 – tungsten-
                                                   carbide supports, 3 – moved piston, 4 – thrust-bearing, 5 – clamping
                                                   nut, 6 – holder, 7 – springs, 8- adjusting systems.
                                                          The application of the shear deformation decreases the
                                                 structure-transition hysteresis and allows one to obtain more
                                                 homogeneous phase. Using DACS and Raman scattering first
                                                 several metastable phases of the C60 fullerite were found with the
pressure increase. At pressure above 20 GPa the metastable phase C60 has high elastic properties that enabled one to
suppose polymerization of C60 molecules [1]. X-ray diffraction and Raman spectra confirmed irreversible
transformation of the molecular C70 structure into superhard amorphous phase under high-pressure and shear-
deformation condition what lowered pressure of phase transition [2]. With use of DACS and Raman scattering we
have studied the phase transitions in SiC. The appearance of new SiC phase is observed by disappearance of LO and
TO phonons at 104 GPa. The structure of this phase is a cubic type of NaCl.
         At present the investigations of structure and properties of new materials produced by polymerization of
C60 and C70 under HPHT in situ and quenchable states are developed. A set of new structures are revealed and
included to International Powder Diffraction Data. The Raman, IR and luminescence spectra of new phases are
studied [3]. The P-T maps are designed for C60 and C70 phases. The compressibility measurements of 3D-
polymerized C60 by X-ray diffraction allowed one to determine bulk modulus of B o  540 80 GPa that is
comparable to bulk modulus of diamond.
                                            The Raman spectra of 3D-polymerized phases are changed: narrow lines
                                  inherent to molecular structure converted to broad band that was interpreted as the
          1
                                  structural transition from molecular structure to three-dimensional net with a
                                  formation of the covalent intermolecular bonds. Using the X-ray diffraction data
                                  and the quantum-chemical simulation, the structure of 3D-polymerized C60 was
                                  proposed and the lattice-dynamical analysis including both two- and three-particle
                                  interactions was carried out, the density of vibrational states (DVS) was computed
                                  and it was shown that DVS correlates with the observed Raman spectra (Fig. 2).
          2                       Fig. 2. The density of vibrational states (1) and the Raman spectrum (2) of 3D-
                                  polymerized C60 phase [4].

                                                   New carbon phase that corresponds to “intermediate” structure between
                                          graphite and diamond with sp2- and sp3-bonds were revealed in diamond after
    0        500    1000    1500     2000
                                           irradiation by fast neutrons. The computed vibrational spectrum for this structure
                       -1
               Wavenumber, cm
                                           was in agreement with the Raman spectrum. The structure of this carbon phase
                                 и спектр by
was Вычисленная плотность (1) studiedКРС the high-resolution electron microscopy and it is found its conversion into
      (2) 3D-полимеризованной фазы С60
graphite under electron beam.

    1.   V.Blank, M.Popov, S.Buga, V.Davydov, V.N.Denisov, A.N.Ivlev, B.N.Mavrin. Is C 60 fullerite harder than
         diamond? Phys.Lett., A188, 281 (1994).
    2.   V.D.Blank, K.V.Gogolinskii, V.N.Denisov, V.A.Ivdenko, B.N.Mavrin, N.R.Serebryanaya, S.N.Sulyanov.
         Mechanical, structural and spectroscopic properties of the C70 fullerite phases produced under high pressure
         with shear deformation. Techn.Phys., 47, 1533 (2002).
    3.   M.Popov, Y.Koga, S.Fujiwara, B.N.Mavrin, V.D.Blank. Carbon nanocluster-based superhard materials.
         New Diamond and Frontier Carbon Technology, 12, 229 (2002).
    4.   L.A.Chernozatonskii, N.R.Serebryanaya, B.N.Mavrin. The superhard crystalline three-dimensional
         polymerized C60 phase. Chem.Phys.Lett., 316, 199 (2000).

				
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