Fullerenes, a new allotrope of carbon, are hollow spherical all carbon molecules composed of six-membered and five-membered rings. Structural studies on C60 and C70 in the solid state at ambient and high pressure are reviewed Phase transitions under high pressures are associated with molecular rotation, orientational ordering, polymerization, and/or crushing of molecules. Tentative p-T phase diagrams for solid C60 and C70 are given. Under appropriate pressure and temperatures, fullerenes in the solid state transform to polymers and diamond. Bulk moduli at low pressures (≤1GPa) are also summarized.
Materials composed of light elements, such as diamond, cubic BN, borides, carbides and nitrides, show extreme features in mechanical, thermal, electronic and optical properties based on small and light atoms strongly bonded to each other. It seems various compositions can be realized from the same combination of elements. It also seems that there are still many materials left for new discovery in this field of materials. Modern extreme condition techniques, including static and dynamic high pressures have revealed several new materials with the B-C-N compositions.
New cyclic conjugated oligomers were synthesized by reacting diphenyldiacetylene and phenylacetylene under high pressure below 1 GPa. The optical limiting properties of the oligomers were investigated. At low input fluence, the transmittance of the toluene solution obeyed the Beer-Lambert law. Above the threshold of the input fluence, the transmittance decreased with input fluence. The oligomers had an optical limiting property. Furthermore, a unique class of conjugated compounds composed of the derivative of condensed polycyclic aromatic compound with the phenyl group and diphenyldiacetylene oligomer was synthesized with appearance of a gas by annealing of diphenyldiacetylene under elevated pressure. The electrorheological (ER) effect of the suspension of the compound showed the high-temperature working limit to be at least 100°C
Recent trends in shock compression research and essential points of view are briefly reviewed. Such aspects have led to the development of SCARQ (Shock compression and Rapid Ouenching) method for exploring new materials, especially carbon. Some examples of new carbon phases and applications to investigating the transition mechanism from graphite to diamond are also reviewed in order to verify the SCARQ method.
Synthesis of polycrystalline diamond compact (PCD) with high heat resistant properties is a big challenge for specialized abrasive application such as in cutting tools, in rock dills etc. The present paper reviews the sintering behavior of natural diamond powder-magnesium carbonate system under the conditions of 7. 7 GPa and 1850-2450°C and its thermal resistant properties. Neither graphitization nor crackings were observed either in or on the compact after the heat treatment between 900∼1400°C for 30 min in vacuum. PCD after the treatment at 1400°C had a high hardness of 55 GPa in Knoop hardness scale. This result suggests that magnesium carbonate is a superior additive for synthesis of PCD with high heat resistant properties.
This paper presents the outline of the temperature gradient method at high pressures and high temperatures for the epitaxial growth of a high purity diamond single crystal. Several elimination techniques of the impurities (mainly nitrogen atoms) in a single crystal are discussed. High purity diamond single crystals, containing impurities as low as 0. 1 ppm, are successfully grown up to 1 or 2 carats by adding titanium and copper in the solvent bath in the temperature gradient method. In order to reduce the nitrogen content of a solvent bath, titanium is added as a nitrogen getter, while copper is added to decompose titanium-carbide which is contained in a crystal as bulky inclusion by adding of titanium.
Theoretical and experimental aspects of a class of new cupric oxides called spin ladder coumpounds will be summarized, where the ladders are made from antiferromagnetic chains of S=1/2 spins by connecting them together with inter-chain antiferromagnetic bonds. Hole carriers doped into evenleg ladders have been predicted to pair, and possibly superconduct. By means of high pressure synthesis at 3-6 GPa and 1200 K, typically, two kinds of 2-leg ladder compounds SrCu2O3 and LaCuO2. 5 and a 3-leg ladder compound Sr2Cu3O5 have been prepared. Their magnetic and electrical properties will be compared with theoretical predictions.
An experimental apparatus for precise measurement of the critical parameters for fluids and fluid mixtures is described in detail. The apparatus can be used in the temperature range from 250 to 500 K at pressures up to 100 MPa.