By using high-energy and high-brilliant synchrotron radiation source in ESRF and PF, an angle-dispersive powder x-ray diffraction study on oxygen has been carried out up to 117 GPa at room temperature. A new highpressure structural transition was observed at 96 GPa and explained as an isostructural one with a discontinuous change of lattice constants in a monoclinic cell. Metallization for oxygen reported by S. Desgreniers et al. [1] is ascribed to the transtion.

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High quality diffraction data of high pressure phases of bismuth, Bi III, Bi III' and Bi IV, were obtained by using the high energy Synchrotron Radiation. Based on the observed diffraction data, crystal structures of these phases have been solved as, Bi III : tetragonal structure with unit cell parameters of a=0. 8680 ± 0. 0005 nm and c=0. 4248 ± 0. 0003 nm at 3. 2 GPa, Bi III': the same structure as Bi III, and Bi IV : monoclinic structure with unit cell parameters of a=0. 6463 ± 0. 0005nm, b=0. 6460 ± 0. 0005nm, c=0. 6582 ± 0. 0006 nm and γ=118. 84 ± 0. 05°at 3. 9 GPa and 503 K. The relations of atomic arrangements between Bi III and Bi V, Bu IV and Bi V are discussed.

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Pressure-induced amorphization is a kinetically hindered phenomenon. The amorphization has been a topic not only in the field of high pressure physics but also in the field of earth science for the last decade. The amorphization of minerals will play an important role to understand the mechanism of deep-forcus earthquakes in the subduction zone, the rheological properties of the slub and the recycling water in the mantle, and so on. In this article, the pressure-induced amorphization of silicates and germanates will be reviewed from the view point of the crystal structures and our resent experiments using the synchrotron radiation will be introduced.

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Recent advance in X-ray Absorption Fine Structure (XAFS) study under pressure is reviewed. After a brief introduction to XAFS and its applications to high-pressure studies, recent development of XAFS measurements under pressure at the Photon Factory is presented. We successfully obtained X-ray absorption spectra at pressures up to 10 GPa and temperatures up to 700°C using a multi-anvil type apparatus, MAX90. Results of our studies on crystalline selenium, amorphous selenium and isolated selenium chains are presented.

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Mössbauer spectroscopic studies of pressure-induced transition from antiferro- to ferromagnetism of Fe in SrFeO₃ at 74 GPa has been performed using a diamond anvil cell (DAC) and the nuclear forward scattering of synchrotron radiation under external magnetic field. Brief description of the principles in Mössbauer spectroscopy using a radio-isotope g-ray source has been given. The basic concept and a method to detect the nuclear forward scattering with synchrotron radiation have been explained briefly.

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A newly developed angle-dispersive diffraction measurement system for highpressure experiments is reviewed. This system has an optical device called Radial Slit, which is consisted with multiple collimators aligned radially. This eliminates the diffraction from the materials surrounding the sample, so that we can measure diffraction from samples in a multi-anvil press by an imaging-plate (IP). Performance of the Radial Slit has been evaluated to be satisfactory, and diffraction patterns of crystal corundum and glassy silica have successfully been obtained using this system.

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In this article, the important role of the synchrotron radiation in the field of spectroscopic study under high pressure up to 20 GPa in the infrared region is emphasized. As a typical example of such experiments which became possible to perform, the experiment on the surface phonon of CdS microcrystals under high pressure using a DAC is presented. Through an analysis of the energy shifts of the surface phonon with pressure, we found that the magnitude of the critical pressure indicating a structural phase transition in the microcrystal differs from that for the bulk.

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Doiamond compact (polycrystalline Diamond: PCD) is the material produced by sintering diamond powder under ultra-high pressure and high temperature conditions. It has been widely used as cutting tools, wire drawing dies, rock drilling bits and wear-resistant parts. This paper describes in outline the kinds and the applications of commercial PCD, the manufacuturing process, sintering mechanism and cutting performances of PCD for cutting tools and the relation between PCD and recent CVD diamond tools.

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Heterocyclic compounds are used now in various fields, and many reports have been published on the synthesis of these compounds every year. This article deals with the studies in our group on the synthesis of heterocyclic compounds including sulfur or nitrogen under high pressure. Nitriles, cianamides, carbon disulfide, isocyanates, and isothiocyanates were good reagents for high pressure synthesis and led to some novel reactions different from those at ordinary pressure. The reactions of these reagents under high pressure have a possibility of developing new synthetic methods of heterocyclic compounds.

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