B.N. Mavrin

Ultrahard and superhard carbon phases produced from C60 by heating at high pressure: structural and Raman studies

Investigations of X-ray diffraction patterns, Raman spectra, hardness and other physical properties were carried out for fullerite after a heat treatment up to 1830 K at 9.5 and 13 GPa nonhydrostatic pressure of bulk samples. Both superhard and ultrahard forms of carbon have been obtained from C60 at 620–1830 K. The hardness of the materials exceeded that of diamond. The X-ray and Raman measurements have shown that both crystal structures and fullerene molecules were retained in superhard and ultrahard states, but a gradual increase of disorder occurred and a random network of linked molecules at high temperatures was formed.

Phase transformations in solid C60 at high-pressure-high-temperature treatment and the structure of 3D polymerized fullerites

New data concerning the solid C60 phase transformations in the pressure-temperature range P = 6.5–13 GPa, T = 300–2100 K and nonhydrostatic conditions are presented and plotted in the P-T coordinates. The structure of superhard and ultrahard carbon phases obtained with these conditions is investigated by X-ray powder diffractometry and Raman scattering. New crystal structures of distorted bcc type and transient to diamond states are revealed in the synthesized samples. Fragments of different lengths of polymerized fullerene cages are found from resonance Raman spectra of the samples obtained at P = 13 GPa and T < 1200 K.

Structures and physical properties of superhard and ultrahard 3D polymerized fullerites created from solid C60 by high pressure high temperature treatment

Abstract Superhard and ultrahard phases of C60 were synthesized by quenching at high pressures up to 13 GPa and high temperatures in the 300–2100 K range. The structures of the samples are discussed on the basis of X-ray and Raman spectra and electron microscopy data. The following physical properties of hard samples were studied: specific gravity; specific heat in the range 400–600 K; sound velocities; elastic moduli; electrical properties; resistance to uniaxial stress; stability against oxidation. These properties are different from those of diamond and other carbon forms. The hardness of ultrahard fullerites exceeds the hardness of diamond.

POLYMERIZATION AND PHASE DIAGRAM OF SOLID C70 AFTER HIGH-PRESSURE-HIGH-TEMPERATURE TREATMENT

Abstract For the first time investigations of structure and physical properties of C 70 after treatment at 4 ≤ P ≤ 12.5 GPa and 300 ≤ T ≤ 1770 K were carried out by X-ray, Raman and infrared spectroscopy. The results are plotted in a ( P , T ) diagram. The new superhard 3D-polymerized tetragonal phase has been found at P ≥ 9.5 GPa. The superhard disordered state of samples produced from C 70 at 12.5 GPa with a hardness close to that of (100)-face diamond has also been found.

Hard disordered phases produced at high-pressure–high-temperature treatment of C60

Abstract X-ray diffraction, hardness, conductivity, Raman and infrared studies of solid C 60 subjected simultaneously to high pressure at 8xa0GPa and temperatures up to 1820xa0K have been carried out. A hard disordered state is formed at temperatures higher than 920xa0K and a cross-linked layered structure is proposed for this state. Crystalline phases obtained at T 60 cages and formation of an amorphous structure. The 3-D polymerization of solid C 60 at high-pressure–high-temperature treatment is discussed.

Structure and properties of C60 and C70 phases produced under 15 GPa pressure and high temperature

Abstract The fullerites C 60 and C 70 have been treated at high pressure, 15xa0GPa, and high temperatures 300–1820xa0K, using the toroid apparatus. The value of 15xa0GPa has been fixed by the abrupt change of electroresistivity of ZnS. X-ray diffraction and Raman spectra confirm the realization of 3D-polymerized phases in these fullerites at 15xa0GPa. The formation of superhard phases with high elastic properties is begun at temperature 100xa0K lower than that it was at 13xa0GPa. The (P, T) maps of C 70 and C 60 are extended to 15xa0GPa.

Hard diamond-like layers produced during DIII-D tokamak operations

Abstract Measurement of the hardness of carbon films, obtained by the exposure of a graphite sample to the tokamak divertor plasma and the deposition of the eroded material on Si substrates, has shown the unexpected result that their hardness was very high. The hardness was about 10–20 GPa, which is close to the hardness of sapphire. We have studied the structural and optical properties of these films by Raman and infrared spectroscopy. The Raman spectra are consistent with a high hardness. The graphite-like Raman band at 1515 cm −1 is down-shifted, which indicates the presence of both sp 2 and sp 3 bonds in the cross-linked structure of the films which is typical for hard carbon films. From the transmission spectra it is found that the band-gap absorption edge is not lower than that of Si. Infrared spectra show a triplet around 2900 cm −1 , which is assigned to the CH stretching modes.