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High Pressure Commission workshop

The High Pressure Commission of the IUCr held an international workshop at the Argonne National Laboratory, Nov. 14-17, 1998, entitled "Synchrotron, Neutron and Laboratory Source Crystallography at High Pressure". This was the first of the Commission's activities since it was formed at the Seattle Congress in 1996. The formal sessions were illustrative of the full range of crystallography using high-pressure techniques. The IUCr, The Center for High Pressure Research (CHiPR), GeoSoilEnviro-Consortium for Advanced Radiation Sources (GSECARS) and the Advanced Photon Source (APS) provided financial support for the meeting. Most of the program responsibilities were borne by the Commission, with John Parise acting as chair of the local and program committees, working closely with Commission chair, Richard Nelmes. We would like to acknowledge the assistance of N. Lazarz (Sectors Coordinator for GSECARS at the APS, Y. Wang, M. Rivers, D. Franklin, J. Brunsvold (ANL Conference Services) and other GSECARS staff.

The oral sessions and over 75 poster presentations emphasized the very latest science and techniques. The meeting attracted 117 participants representing 59 institutions and 14 countries, including 23 young scientists, 17 of whom received support from IUCr funds. A number of the poster presenters gave a 3 minute introduction to their work in a special session on facilities and techniques. Several other invited "poster orals" were added to the oral program.

Participants at the Workshop "Synchrotron, Neutron and Laboratory Source Crystallography at High Pressure". Photo courtesy of John Parise.

The first session highlighted recent developments in "soft matter". This sub-discipline, being covered in a forum of the High-Pressure Commission for the first time, was introduced by a talk from S. Gruner, who outlined the potential for using the large effects observed with modest application of pressure and concluded with a summary of the technical challenges. The session included stimulating presentations on pressure-induced unfolding of proteins (G. Hummer), phase behavior of mesophases and proteins (R. Winter), and packing of alkanes under pressure (H. King). Poster orals covered the structure of melamine (P. Dera) and the high-pressure behavior of gelatin (W. Poon).

Elasticity and rheology are areas important to members of the Earth and materials community. Recent developments in theory and in the design of apparatus at synchrotron beamlines has allowed interpretation of changes in powder diffraction patterns in terms of relaxation and stress-strain behaviors induced by heating at high pressures. T. Duffy and A. Kavner presented their latest results on the determination of lattice strains and P/T calibrations in the diamond anvil cell. Unfortunately, a bar on Indian scientists entering a DoE facility prevented A. Singh from attending.

On Saturday evening J. Jorgensen traced the history of "Thirty Years of Neutron Diffraction at High Pressure" which, in large part, began and flourished at the Argonne National Lab.

The two sessions on technical developments covered the latest in optimizing the diffraction experiment for precision (M. Kunz and R. Angel), unit-cell indexing and structure solution from complex powder data (S. Belmonte), and the use of maximum entropy techniques to extract information from a powder diffraction experiment (M. Takata). Poster orals dealt with the accurate determination of the pressure scale (D. Weidner) and development of drilled diamonds to permit the use of low energy x-rays (C. Colle). This latter development complements recent progress in the use of beryllium gaskets by the group at the Geophysical Laboratory. Y. Katayama presented new developments in studies of liquids at high P and T, and G. Fiquet presented technical developments that are taking studies of earth materials close to the conditions of the Earth's lower mantle and core.

Theoretical presentations, by R. Cohen and S. Scandolo, emphasized transitions and behavior under extreme conditions important to the Earth and other planetary interiors. S. Saxena presented some corresponding experimental results obtained from both synchrotron and laboratory-based sources employing imaging plate and CCD detectors. Twenty invited oral presentations of posters on facilities and techniques followed a talk by G. Shen concerning developments of the APS.

Sessions were devoted to magnetism, superconductivity, general bonding and materials characteristics as a function of pressure. The first of these included presentations on spin-Peierls transitions (M. Nishi), neutron diffraction magnetic studies to 50 GPa (I. Goncharenko), studies of GMR manganites (D. Argyriou), superconductivity (D. Sheptyakov) and a comparison of the effects of applied vs. chemical pressure in magnetic studies (I. Mirebeau). A session emphasizing structure, bonding and materials featured talks by P. McMillan on twinning and packing of boron-rich clusters, H. Fujihisa on the structures of HCl and HBr, K. Syassen on the new structures of Cs-V and Si-VI, K. Kusaba on phase equilibrium of group II-VI semiconductors at high P and T, and D. Haüsermann on the latest results from the very active group at beamline ID30 at the ESRF, including work on semiconductor phase diagrams in a Paris-Edinburgh large-volume cell. M. McMahon complemented this session with an invited poster oral on new structures and transitions in GaAs.

The final day featured spirited sessions on ices and hydrogen bonding, and spectroscopic studies. W. Kuhs provided an overview of ices and ice clathrates at lower pressures, followed by talks dealing with phase transitions and structures of liquid water and amorphous (glassy) and crystalline ice (D. Klug and M.-C. Bellissent-Funel). J. Loveday presented results of the Paris-Edinburgh collaboration on neutron diffraction study of ices up to 25GPa, and R. Hemley on studies of ice to megabar pressures and D. Marx on complementary ab initio calculations of protons in ice in that range.

The final session of the meeting, "spectroscopic studies at high pressure", covered the latest developments in what is/will be possible in 1999. S. Klotz presented work much extending the pressure range of inelastic neutron scattering. M. Pasternak spoke of his Mössbauer spectroscopy on FeO and advanced pressure cells for studies beyond 100GPa. W. Bassett and R. Mayanovic gave closely-related talks dealing with the design of a special DAC to allow EXAFS studies at low-energy edges. They presented results on zinc (II) complexes in hydrothermal fluids. The meeting was given a splendid inale with a talk from H. Mao on recent developments in X-ray spectroscopy and the many exciting prospects of the new beamline concept at the APS (the High Pressure Collaborative Access Team or HP-CAT).

Tours of the APS and IPNS facilities, were conducted in parallel with posters one afternoon. The highlight of the banquet was a presentation by Malcolm McMahon of essential linguistic guidelines for those attending the Glasgow Congress. In bare knees and a tartan car-rug, he assailed the crowd with some of the finest Scots humor heard since Sean Connery played that Russian submarine commander!

The participants plan to meet again in Glasgow where six oral sessions will continue to develop many of the topics of this landmark meeting.

John Parise and Richard Nelmes