Meeting Report

Crystallography at High Pressure and High Temperature using X-rays and Neutrons

Nearly 80 high-pressure scientists from 13 countries gathered at the picturesque site of Spring-8, Hyogo, Japan on September 30, 2000 for the international workshop on "Crystallography at High Pressure and High Temperature using X-rays and Neutrons" (photo 1). The workshop was jointly organized by the IUCr Commission on High Pressure, the SRRC Japan Atomic Energy Research Institute, and the Japan Synchrotron Radiation Research Institute (JSRRI). Prior to the workshop a site tour was arranged to show participants the high-pressure activities at Spring-8. During the three-day long workshop, 25 oral and 43 poster presentations were made, and participants appreciated the ample time allowed for discussion after each talk and the short oral presentation of each poster.

Participants in front of the main building of Spring-8

The workshop, began with a welcome address by Osamu Shimomura (Spring-8), and consisted of several sessions: ‘Random Systems’ and ‘Novel Structures of Simple Systems’ on the first day, ‘Geophysics’ and a general Poster Session on the second day, and ‘Crystal Chemistry and Materials Science’ on the last day.

The first order transitions commonly encountered in solids are rare in the liquid state, but Y. Katayama (Spring-8, Hyogo, Japan) showed pressure-induced first order transitions in molten phosphorus involving a transition from molecular liquid to polymeric liquid. K. Tamura (Hiroshima University, Japan) discussed the structure factors of mercury and selenium in the liquid state and pointed out that even at moderately low pressures interesting behavior in the liquid state can be observed. Then P. Postorino (University of Rome "La Sapienza", Italy) presented measurements of short range order in liquid iodine over a range of pressure and temperature. The observed increase in bond length under pressure was attributed to the progressive weakening of the molecular units, which finally leads to an insulator-metal transition. A similarity between these results and those on liquid rubidium, cesium and mercury leads to the concept of a universal fluid in the insulator-metal transition region. K. Funakoshi (Spring-8, Hyogo, Japan) talked about an x-ray radiographic technique that uses in-situ observations of an x-ray opaque object sinking in a melt to make measurements of viscosity.

In the ‘Novel Structures of Simple Systems’ session, K. Syassen (MPI, Stuttgart, Germany) pointed out that alkali metals have played an important role in the development of the nearly-free-electron model of simple sp band metals. Under high compression the electrons in heavy alkali metals are no longer free but tend to behave like the electrons in monovalent d transition metals. The s to d transition under high compression is the main driving force for the structural transitions in heavy alkalis. The associated talk by M. Hanfland (ESRF, Grenoble, France) concentrated on the high-pressure behavior of lithium, which shows a number of interesting transitions. The ease with which lithium under high pressure at room temperature diffuses in diamond and its low diffracting power make the diffraction experiments extremely difficult. F. Gorelli (European Laboratory for Non-linear Spectroscopy, Italy) and Y. Akahama (Himeji Institute of Technology, Hyogo, Japan) discussed the P-T phase diagram of oxygen. M. Nicol (University of Nevada, USA) covered the kinetics aspects of the fcc-to-hcp transition in xenon and krypton. The two phases are found to coexist over a wide pressure range. Small energy differences between the two phases and anisotropy of the stress field are the reasons suggested for the co-existence of two phases over a large pressure range. The structure of the high-pressure phases of ND₄I and ND₄Br using time-of-flight neutron diffraction were reported by D. P. Kozlenko (Frank Laboratory of Neutron Physics, Moscow, Russia).

F. H. Ree (LLNL, USA) used Monte Carlo and molecular dynamics simulations to get an insight into complex phenomena such as melting of carbon, the behaviour of liquid carbon, phase transformations in graphite and diamond clusters, and the kinetics of cluster growth. The results on the quantum distributions of protons in three high-pressure phases of solid molecular hydrogen obtained from first principles path-integral molecular dynamics were presented by S. Tsuneyuki (University of Tokyo, Kashiwa, Japan). These results are significantly different from the predictions based on conventional simulation with a classical treatment of protons. J. S. Tse (NRC, Ottawa Canada) and R. Ahuja (Uppsala University, Sweden) covered the theoretical aspects of chemical bonding and structural transitions in alkali metals.

T. Kubo (Tohoku University, Sendai, Japan) reported the kinetics of the alpha-beta transformation in forsterite as obtained from time resolved x-ray diffraction measurements. M. Kunz (Laboratory of Crystallography, ETH Zurich, Switzerland) presented studies on titanite and zircon under high P-T conditions and reported the P-V-T equation of state for the two polymorphs of titanite. The PV-relation of U-bearing partially metamict zircon measured during increasing pressure was anomalous, but normal when the volume changes were measured during decreasing pressure. This suggested a possible stepwise collapse and healing of metamict zones in zircon. The various aspects of precise pressure measurements, structural refinements and accurate equations of state were discussed by D. Andrault (Institut de Physique du Globe de Paris, France) with examples of materials of geological interest. T. Uchida (CARS, University of Chicago, USA) reviewed diffraction and imaging studies on materials relevant to the Earth’s core. G. Shen (CARS, University of Chicago, USA) discussed experiments on iron and MgSiO₃ under high P-T conditions. J. S. Loveday (University of Edinburgh, Edinburgh, U. K.) discussed the high-pressure behavior of methane clathrate hydrate, a major source of methane within the Earth and a model system for the study of hydrophobic interactions. L. Dubrovinsky (Uppsala University, Sweden) discussed the results of the studies on Fe-Ni system at high P-T conditions with reference to the modeling of the Earth’s core.

M. Mezouar (ESRF, Grenoble, France) reviewed some recent high-pressure studies in the area of materials science and specifically discussed 3D polymerization of C₆₀, non-catalytic synthesis of cubic boron nitride, and synthesis of cubic boron carbonitride through a direct phase transformation of a graphite-like boron carbonitride precursor at high P-T conditions. W. Utsumi (Spring-8, Hyogo, Japan) discussed the formation process of diamond from graphite and of cubic boron carbonitride as obtained from in situ time-resolved x-ray diffraction.

K. Takemura (NIRIM, Tsukuba, Japan) presented x-ray diffraction data on several materials compressed to 70-80 GPa in a helium pressure transmitting medium. These data suggest a strong correlation between the diffraction line width and the magnitude of uniaxial stress component. A. K. Singh (NAL, Bangalore, India) discussed the theoretical aspects of line broadening caused by uniaxial stress and presented diffraction data on beta brass to support the theory.

Y. Fujii (Tokyo University, Ibaraki, Japan) made the closing remarks.

All the participants stayed at the guest house of Spring-8, and fully enjoyed not only the daytime sessions but also the evening sessions held at the ‘tatami’ room of the guest house (photo 2).

Serious business after 9 PM

Copyright © International Union of Crystallography