Mechanism of formation of the superhard disordered graphite-like phase from fullerite C₆₀ under pressure

Abstract

Comparing the transmission electron microscopy and x-ray diffraction data for a disordered graphite-like (sp2-bonded) carbon phase (DGCP) synthesized from fullerite C60 at high temperatures in the pressure interval from 1.5 to 8 GPa, we show that the nanocluster structure, long-range correlations for orientation of clusters, lamellar and tweed morphology, and possible macroscopic anisotropy are intrinsic properties of the DGCP, and that they can be recognized as a signature of stresses in the parent phase at different scales from the atomic level (atomic density modulation) to the macroscopic one (non-hydrostatic pressure environment). These data indicate that the mechanism of the formation of the DGCP from large-molecule crystalline carbon material, such as C60, is quite uncommon in the standard classification for the first-order phase transitions since it displays features typical for both diffusion and martensitic mechanisms, e.g., a strong topological rearrangement of covalent bonds and a crystallographic-like relation between crystalline parent and disordered product phases, respectively.

Nanoarchitectured materials composed of fullerene-like spheroids and disordered graphene layers with tunable mechanical properties

“…Both structures are dominated by intense peaks at B1.9, B3.1 and B5.3 Å À 1 in the momentum transfer (Q) space, corresponding to interplanar spacings of B3.3, B2.0 and B1.2 Å, in broad agreement with the (002), (100)/(101) and (110)/(112) d-spacings of graphite. These peaks, significantly broader than crystalline graphite, are similar to those observed in the disordered carbon phase produced by compressing C 60 to high pressures 29 . The weak peaks around 3.8 and 6.2 Å À 1 are high order diffractions of the first two strong peaks.…”

Thermodynamic properties of graphite-like nanostructures prepared by thermobaric treatment of fullerite C60

“…The synthetic procedure and selected physicochemical characteris tics of the substances have been reported earlier. [11][12][13] Here it should be noted that, according to the kinetic phase diagram of fullerite C 60 (see Refs 5 and 8), under the p-T treatment conditions mentioned above the molecular cage of C 60 breaks down with the formation of GNS containing small amounts of sp 3 hybridized C atoms. 13 The temperature dependences of the heat capacities of sam ples I and II in the range 7-360 K were measured following a known procedure 18,19 using a BKT 3 automated adiabatic vac uum calorimeter.…”

“…[11][12][13] Here it should be noted that, according to the kinetic phase diagram of fullerite C 60 (see Refs 5 and 8), under the p-T treatment conditions mentioned above the molecular cage of C 60 breaks down with the formation of GNS containing small amounts of sp 3 hybridized C atoms. 13 The temperature dependences of the heat capacities of sam ples I and II in the range 7-360 K were measured following a known procedure 18,19 using a BKT 3 automated adiabatic vac uum calorimeter. The accuracy of the heat capacity measure ments was at most ±2% near 10 K, ±0.5% in the temperature interval 15-40 K, and ±0.2% in the range from 40 to 360 K. The temperatures of physical transformations were determined with an accuracy of at least ±0.02 K.…”

Pressure-induced transformation and superhard phase in fullerenes: The effect of solvent intercalation

“…Thanks to the strong C-C covalent bonds, many carbon phases, including both crystalline and noncrystalline forms, are found to exhibit high hardness and have important technological applications in different fields. The structures and the formation mechanisms of hard carbon phases thus have been subjected to numerous experimental [1][2][3][4][5][6][7][8][9] and theoretical [10,11] works.…”

“…[1][2][3][4][5][6] At high pressure and high temperature conditions, C 60 may transform into 3D polymer with hardness comparable to that of cubic BN or into amorphous fullerite phases. Some amorphous phases produced show super-or ultrahardness, such that they can even break diamonds.…”