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 . 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 . 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 . 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 . 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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