The discovery of superconductivity in diamond opened up a new field of superconductivity in doped semiconductor. Using the chemical vapor deposition (CVD) method, polycrystalline and homoepitaxial superconducting diamond films have been successfully synthesized. These films show relatively high superconducting transition temperatures, particularly in homoepitaxial (111) film that showed the highest superconducting transition temperature of Tc = 11.4 K. Since high quality and large films can be obtained by the CVD method, many fundamental physical measurements were carried out to understand the mechanism of superconductivity in diamond. In this report, the recent data about superconducting properties of heavily boron-doped diamond are discussed.

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High-purity (binder-less) polycrystalline diamond can be referred to as an ideal super-hard material that has both high mechanical strength and excellent thermal stability. The authors succeeded in the synthesis of dense high-purity polycrystalline diamonds by direct conversion from graphite and non-graphitic carbons under static ultra-high pressure and high temperature. In this article, the synthetic method and some properties of the materials are reviewed. Differences in formation mechanism and properties among high-purity polycrystalline diamonds synthesized from various carbons are also described.

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It reports on the advancement of a recent graphitized carbon material from the viewpoint of dimensionality and application. First of all, the dimensional change and the possible application of fullerene (zero-dimensional graphite), carbon nanotube (one-dimensional), and graphene (two-dimensional) are described. The synthesis of the unique graphite fiber is also mentioned, as an example of obtaining a graphitized material in various forms by the molecular structure of the raw material. Next, making of a high-quality graphite film from a polyimide and its optical and thermal applications are described. It introduces the research of the pressure-induced phase transition from the graphite film to diamond.

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In this article, several high-pressure researches on carbon nanotubes are reviewed after the brief introduction of nanotubes in carbon family. Direct transformation to nanocrystalline diamond from multiwalled carbon nanotubes makes it possible to synthesize a transparent sintered compact without any sintering additive. Result of room temperature compression of multiwalled nanotubes up to 50 GPa suggests strong durability of tubular structure and exhibits no interlayer interaction such as hexagonal diamond formation. Attempts to store high-pressure fluid into nanotubes are also described.

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Fullerene C₆₀ molecules were three-dimensionally polymerized under a high-pressure and high-temperature condition of 15 GPa at 600°C. A single crystal of 3D polymer was obtained from a 2D C₆₀ polymer with a body centered orthorhombic symmetry. The X-ray structural analysis of the 3D polymer revealed that spherical C₆₀ monomer molecules were substantially deformed to cuboidal shapes, each unit being bonded to eight neighboring units at the cuboidal corners to form a body centered orthorhombic lattice. The new 3D polymer was electrically conductive and showed high micro-Vickers hardness comparable to that of cubic BN.

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Recent functional research using pressurization on polyhedral graphite particles "G balls", which are one of carbon nano-structured materials, are reviewed in this article. The high-pressure structural-study shows the polyhedra maintain the graphite phase under pressure higher than 40 GPa. We could understand the closed and solid framework of G balls contributes to stability and high volume elasticity of the graphite phase. Therefore, it is reasonable to suppose that G balls have a hydrogen-barrier effect in addition to a ball-bearing function when they are applied to a solid lubricant inducing rolling friction.

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We have been developing an experiment on laser-induced double-shock compression of diamond foils to a metallic phase by means of impedance-mismatching technique. We measured the reflectivity from the rear side of the diamond foil with a velocity interferometer system for any reflector. The measured reflectivity of the diamond clearly increased with the double compression. Independently measured from an optical pyrometer indicates that the compressed temperature of the diamond was approximately 7300 K, which is much lower than that of the single shock. The experimental results strongly suggest the phase transition from diamond to metallic carbon.

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Phase equilibrium relations at high pressures are required in practical use, such as in the design and operation of supercritical fluid extraction. High-pressure phase equilibrium measurements of fluid mixtures cannot simply generate the reliable data. In the present review, the reference data are first mentioned. For the development of mixing rules in equations of state for fluid mixtures, reliable standard phase equilibrium data of fluid mixtures at high pressures are required as reference of standard. Next, recent researches on the phase equilibrium measurements at high pressures are reviewed by classifying the types of the experimental apparatus: static, circulation, static-circulation, flow, synthetic, and mass balance. All experimental methods and apparatus seem consistent, with the exception of some special cases. The experimental data obtained by the different experimental methods and apparatus should agree one another. In the high-pressure phase equilibrium measurements of fluid mixtures just a minor poor treatment in the experiment causes a large error in the final experimental results, and all experimental treatments should be carefully consistent to establish the reliable consistent data.

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In this article, the valuable methods of prediction and correlation for phase equilibria formed by water and hydrocarbons mixtures at high temperatures and pressures are introduced and discussed. The numerical calculations by equation of state, molecular simulation and based on quantum chemical calculation are shown. The main numerical formulas and characteristics of each method are described.

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