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The fullerites C60 and C70 have been treated at high pressure, 15 GPa, and high temperatures 300–1820 K, using the toroid apparatus. The value of 15 GPa 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 15 GPa. The formation of superhard phases with high elastic properties is begun at temperature 100 K lower than that it was at 13 GPa. The (P, T) maps of C70 and C60 are extended to 15 GPa.

Polymeric structures on the basis of La@C 82 endofullerene were synthesized and investigated for the first time. Bulk samples of about 10 mg weight were obtained by static high-pressure-high-temperature treatment at 9.5 GPa and 520; 720 K. The structure of quenched samples was studied by powder X-ray diffraction and transmission electron microscopy. Several new crystalline structures were found and attributed to the formation of dimers, 2D- and 3D-polymeric structures. Magnetic susceptibility of synthesized samples was investigated in the temperature range 5-300 K.

Ultrahard and superhard fullerites are a new class of the carbon materials produced recently by bulk polymerization of C60 and C70 fullerenes under high-pressure-high-temperature treatment. We applied the acoustic microscopy technique to measuring longitudinal and shear sound velocities and determinating elastic constants of the super- and ultra-hard polimerized fullerites. Bulk elastic modulus of ultrahard fullerites is essentially higher than diamond's one, while the shear modulus and the Young modulus are less. The acoustic microscopy images reflected microstructure of fullerite speciments were obtained.

Velocities of longitudinal and transverse acoustic waves were measured for the first time in disordered cross-linked layered structures obtained by static thermobaric treatment of C 60 powder at pressures P =8–11 GPa and temperatures up to T =1650 K. Elastic constants are evaluated and compared with known data for other superhard and ultrahard fullerites, polycrystalline and monocrystal diamonds, graphite and pristine C 60 .

For the first time investigations of structure and physical properties of C70 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 C70 at 12.5 GPa with a hardness close to that of (100)-face diamond has also been found.

X-ray diffraction, hardness, conductivity, Raman and infrared studies of solid C 60 subjected simultaneously to high pressure at 8 GPa and temperatures up to 1820 K have been carried out. A hard disordered state is formed at temperatures higher than 920 K 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.

C60 fullerite samples synthesized under a pressure of P = 13 GPa and temperatures of Ts = 770 − 2100 K were studied by scanning microphotoluminescence (MPL) at room temperature. The MPL of cleaved chip surfaces indicates the presence of emitting areas with linear dimensions from 35 to 350 μ. A band at 700 nm, which is characteristic for linear and planar C60 polymers, was revealed in all 3D-polymerized fullerites too. New bands at 1100−2300 nm are observed in PL spectra of substances synthesized at 870 ≤ Ts ≤ 1270 K. Separated areas of several optically active moieties responsible for luminescence in the range 1100−2300 nm were detected by MPL cartography. The origin of this band is tentatively attributed to traps located on C60-oxygen and nitrogen inclusions associated with defects of the crystal lattice.

in the pressure range \rangeunit{8}{13}{GPa} and the temperature range \rangeunit{600}{2100}{K} were studied. These properties are the specific gravity, specific heat in the range \rangeunit{400}{600}{K} , sound velocities, elastic moduli, electrical properties, resistance to uniaxial stress and stability against oxidation. These properties are different from those of diamond and other carbon forms. The hardness of ultrahard fullerites exceed the hardness of diamond. The structures of the samples are described on the basis of X-ray data.

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.

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.

Raman spectra of C60 fullerite at pressures up to 37 GPa with shear deformation are studied. We have found two states at high pressures, that persist after pressure release and have various transparencies in the near IR region. The nontransparent state is formed at 6–18GPa and has a Raman spectrum with broadened bands at frequencies close to those of the initial fullerite. The transparent state was obtained at pressures higher than 18GPa, and the Raman bands are broadened and overlapping in comparison with those of the nontransparent state. We suppose that C60 molecules persist in both states. The transparent state of fullerite shows a hardness higher than that of diamond.

Acoustoelectric current giant quantum oscillations have been measured in LiNbO 3 -Bi 0.99 Sb 0.01 layered structure at H ⩽ 40 kOe and T = 4.2 K along bisectornal C 1 and binary C 2 sample crystallographic axes. Obtained data allows us to estimate the Fermi surface effective cross-section areas. Proposed method is useful for electron and hole energy spectrum investigations in semimetals.

A novel method of high-efficiency cold cathode formation is developed. The technique is based on the growth of nitrogenated carbon nanofibers in a high-pressure apparatus on a graphite substrate. An average nitrogen concentration up to 13% was achieved. The turn-on and threshold fields for such cathodes are substantially lower than those for cathodes based on other carbon materials. A special method of substrate preparation provides strong adhesion of carbon-nitrogen nanomaterial and its durability during long-term cathode operation. It is shown that due to high uniformity, emission efficiency and time reliability, the field emission cathodes based on carbon-nitrogen nanofibers (CNNs) are very promising for high-brightness flat indicators and displays.

Nitrogen containing carbon nanostructures for flat field emission cathodes were synthesized for 40 min in a high isostatic pressure apparatus where the gaseous pressure was 75 MPa and the heat zone temperature was 1500degC. The carbon-nitrogen nanomaterials deposited on graphite substrates were investigated by scanning electron microscopy and infrared spectroscopy. Fowler-Nordheim curves, and the turn-on and threshold fields were extracted by a diode-type tester. High uniformity, field emission efficiency and time reliability of the CN nanofibers based cathodes are good perspective for high brightness flat indicators and displays

A computer-based experimental technique for visualization of pressure distribution and substance flow in diamond anvil cells is presented. It is applied in the investigation of nonlinear elastic properties of ZnSe sample under conditions of the structural phase transition, caused by high pressure and great shear deformations. >