E. A. Ekimov

High-pressure, high-temperature synthesis of SiC-diamond nanocrystalline ceramics

Dense and entirely nanocrystalline diamond–SiC ceramics were synthesized by the infiltration of liquid Si into the nanodiamond body under high-pressure (77 kbar) and high-temperature (1400–2000 °C) conditions. Based on x-ray diffraction and transmission electron microscopy observations, a model of as-synthesized material is proposed, where individual polycrystalline diamond particles are bonded via SiC–diamond nanolayers. The nanolayers provide a very high hardness of the entire specimen up to 51 GPa. The phenomenon of self-stop Si infiltration was detected in this system. This phenomenon can be explained by the closure of pores near the boundary between molten Si and diamond nanopowder due to the formation of SiC inside the pores.

Mechanical Properties and Microstructure of Diamond–SiC Nanocomposites

A bulk composite material close in hardness to diamond was fabricated from nanocrystalline diamond and SiC. The mechanical properties and microstructure of the composite were studied. Youngs modulus of the composite is found to be notably lower than the one following from the additivity rule, which is attributable to the influence of structural defects present in the interfacial zone between SiC and diamond. SiC consists of nanometer-scale grains near the interface and submicron grains in the “pores.”

Global and Local Superconductivity in Boron‐Doped Granular Diamond

Strong granularity-correlated and intragrain modulations of the superconducting order parameter are demonstrated in heavily boron-doped diamond situated not yet in the vicinity of the metal-insulator transition. These modulations at the superconducting state (SC) and at the global normal state (NS) above the resistive superconducting transition, reveal that local Cooper pairing sets in prior to the global phase coherence.

High-pressure high-temperature synthesis and structure of α-tetragonal boron

Abstract Microcrystals of α-tetragonal (α-t) boron with unit cell parameters a=9.05077(6) and c=5.13409(6) Å and measured density 2.16–2.22 g cm−3 were obtained by pyrolysis of decaborane B10H14 at pressures of 8–9 GPa and temperatures of 1100–1600 ○C. The crystal structure is in good agreement with the model proposed by Hoard et al (1958 J. Am. Chem. Soc. 80 4507). However, compared to the original model, we found small deformations of icosahedra and changes in the interatomic distances within the unit cell of the synthesized α-t boron.

Structure and physical properties of nanoclustered graphene synthesized from C60 fullerene under high pressure and high temperature

C60 treatment at 5–8 GPa, ∼1000 °C results in the fullerene cage collapse and transformation to a phase with outstanding mechanical properties. A detailed structural analysis of the phase reveals that it comprised 7–12 layer graphene clusters with lateral dimension of 2–4 nm. Raman spectra of the nanoclustered graphene phase are similar to those of disordered sp2 carbon structure with an admixture of sp3-bonded carbon. The phase is characterized by a high (up to 19 GPa) hardness, relatively low (about 70 GPa) Young modulus and up to 95% elastic recovery, determining excellent wear resistance and good antifriction properties.

Structure and superconductivity of isotope-enriched boron-doped diamond

Abstract Superconducting boron-doped diamond samples were synthesized with isotopes of 10B, 11B, 13C and 12C. We claim the presence of a carbon isotope effect on the superconducting transition temperature, which supports the ‘diamond-carbon’-related nature of superconductivity and the importance of the electron–phonon interaction as the mechanism of superconductivity in diamond. Isotope substitution permits us to relate almost all bands in the Raman spectra of heavily boron-doped diamond to the vibrations of carbon atoms. The 500 cm−1 Raman band shifts with either carbon or boron isotope substitution and may be associated with vibrations of paired or clustered boron. The absence of a superconducting transition (down to 1.6 K) in diamonds synthesized in the Co–C–B system at 1900 K correlates with the small boron concentration deduced from lattice parameters.

High‐Pressure Synthesis of Boron‐Doped Ultrasmall Diamonds from an Organic Compound

The first application of the high-pressure-high-temperature (HPHT) technique for direct production of doped ultrasmall diamonds starting from a one-component organic precursor is reported. Heavily boron-doped diamond nanoparticles with a size below 10 nm are produced by HPHT treatment of 9-borabicyclo [3,3,1]nonane dimer molecules.

High-pressure synthesis and characterization of superconducting boron-doped diamond

Abstract We present a scanning tunneling microscopy/spectroscopy (STM/STS) study of synthetic polycrystalline boron–doped diamond in the temperature range 0.5–4.3 K. At 4.3 K the sample–surface was very non–uniform and tunneling I(V) spectra were typical for p–type semiconductors. After cooling below the superconducting transition temperature, we detected and measured the superconducting gap of diamonds. At temperatures around 0.5 K the energy gap was around 0.8 and 1 mV (for two differentsamples).

Sintering of a Nanodiamond in the Presence of Cobalt

A composite with hardness over 55 GPa is obtained by cobalt infiltration into a nanodiamond at a pressure of 8 GPa. Graphitization of a nanodiamond in pores is found to precede cobalt infiltration into them. In the presence of cobalt, graphite-like carbon is inversely transformed into diamond with a slight time delay and the nanodiamond recrystallizes, a polycrystal diamond frame being formed. The minimum cobalt concentration in compacts required for nanodiamond sintering using the infiltration technique is 6 vol %.

Structure and properties of superelastic hard carbon phase created in fullerene-metal composites by high temperature-high pressure treatment

Treatment of a fullerene soot extract and metal (Co) powder mixture under pressure of 5 and 8 GPa at 1000 °C leads to the transformation of fullerites into superelastic hard phase (SHP) and to simultaneous sintering of the powder mixture to nonporous composite material reinforced by the SHP particles. The structure of the SHP particles reveals a topological relation to the initial fullerite crystal morphology. Upon indentation, the SHP particles demonstrate an elastic recovery of up to 96%. The universal microhardness of the SHP particles HU = 26 GPa, and their microhardness HV = 35 GPa. A high ratio between the microhardness and elastic modulus (HV/E = 0.19-0.21) of the SHP particles makes them perspective candidates for design of materials with superior wear resistance and tribological properties.