M.Yu. Popov

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.

Plasticity of diamond at room temperature and determination of its hardness using an atomic force microscope with an ultrahard C60 fullerite tip

A method has been developed to measure the hardness of superhard materials with an atomic force microscope. By using an indenter made of ultrahard fullerite C60, of hardness superior to that of diamond, plastic deformation of diamond is achieved at room temperature without any crack formation and its hardness is measured.

Effect of a fullerene C60 addition on the strength properties of nanocrystalline copper and aluminum under shock-wave loading

The Hugoniot elastic limit and the spall strength of aluminum and copper samples pressed from a mixture of a metallic powder and 2–5 wt % C60 fullerene powder are measured under a shock loading pressure up to 6 GPa and a strain rate of 105 s−1 by recording and analyzing full wave profiles using a VISAR laser interferometer. It is shown that a 5% C60 fullerene addition to an initial aluminum sample leads to an increase in its Hugoniot elastic limit by an order of magnitude. Mixture copper samples with 2% fullerene also exhibit a multiple increase in the elastic limit as compared to commercial-grade copper. The elastic limits calculated from the wave profiles are 0.82–1.56 GPa for aluminum samples and 1.35–3.46 GPa for copper samples depending on the sample porosity. The spall strength of both aluminum and copper samples with fullerene additions decreases approximately threefold because of the effect of high-hardness fullerene particles, which serve as tensile stress concentrators in a material under dynamic fracture.