REPORT

on the International Workshop of the High Pressure Commission

Orsay, France, September 4-9, 2001

An international workshop "Crystallography at High Pressures —2001" organised by the Commission on High Pressure was held at Orsay, France, September 4-8 2001. The Workshop followed the meetings organized by the Commission at ESRF Grenoble in 1997, APS Argonne in 1998 and the joint meeting between the Commission and JAERI at SPring-8 in 2000. This time, the French national neutron facility Laboratoire Léon Brillouin was chosen as the host organization. As for the previous meetings, the Commission determined the scope of the meeting and provided most of the suggestions for the scientific program. Igor Goncharenko (Commission member) acted as a chair of the Organizing Committee and Richard Nelmes (Commission chair) acted as chair of the Program Committee.

In each triennium — at APS in 1998 and now this Workshop — the Commission holds one meeting that covers the full scope of its activities: structures and transitions, new materials, Earth and planetary sciences, soft and biological matter, physical and chemical properties, theory and computation, and technique developments on synchrotron, neutron and laboratory-based facilities. The scientific program occupied four full days and included 13 oral sessions and a special poster session. It accommodated 33 invited talks, 12 poster orals (including 7 invited) and 49 poster presentations. The Program and Organizing committees put especial efforts into bringing new names into the program. Many of the invited speakers and most of the invited poster orals presenters were young researchers, postdocs or PhD students.

We would like to thank members of the Organizing Committee, Jean-Michel Mignot (vice-chair), Isabelle Mirebeau and Paula Cadavez-Peres, and the meeting would be not have been as successful as it was without all the efforts of Olga Makarova, Bernard Mailleret, Chantal Pomeau, Claude Rousse, Isabelle Rault, Frederique Berger, Jean-Paul Itié and Alain Polian. Finally, all the local arrangements worked extremely well (with the exception of a small drawback coming from a not very reliable bus company!).

The IUCr, CEA (French Commissariat of Atomic Energy), CNRS (French National Centre for Scientific Research) and the French Ministry of Research all contributed to funding of the Workshop. These funds are very gratefully acknowledged and allowed us to support more than 30 young scientists.

The meeting attracted about 115 participants from 15 different countries. The scientific sessions were held at the campus of the Orsay University, 30 km from the centre of Paris. Most of participants opted to stay in Orsay or nearby, enjoying the pleasant environment of the Yvette valley and excellent food in local restaurants.

Participants at the meeting in Orsay

After a welcoming party on the evening of Tuesday 4^th, the scientific program was opened on the morning of Wednesday 5^th, with a session devoted to soft and biological matter. The audience learned about a structural basis for pressure effects in proteins from Paul Urayama, and exciting recent progress in structural refinement of diamond-anvil-cell data from proteins presented by Roger Fourme, and enjoyed a well illustrated talk from Richard Templer on lyotropic phase transitions induced by pressure jumps. Wilson Poon used all his artistic talents to describe a brilliant future for studies of protein dynamics and Amy Lefebvre described nucleation in polymers under pressure. Two poster orals, presented by Gérard Pépy and Isabella Ascone, highlighted results obtained on neutron and soft x-ray facilities.

The program continued with studies of liquid and amorphous systems. Mohamed Mezouar highlighted recent developments at the ID30 beam line (ESRF) for studying liquids under high P-T conditions. Chris Benmore outlined some advantages of neutron techniques (H/D contrast) in studies of critical and sub-critical liquids. And these invited talks were supplemented by a poster oral on pressure driven amorphization (Denis Machon).

After lunch, the program turned to crystal structures and phase transitions. Progress in ab-initio calculations of crystal structures and physical properties was overviewed by Bjoern Winkler. Malcolm McMahon presented new results on several remarkably ‘weird’ structures occurring in simple metals under high pressures. In another theoretical talk, Jianjun Dong predicted new crystal structures in solidified gases. The session ended with Przemyslaw Dera describing experimental studies of H-bonding materials. Various aspects of structural transitions in cristobalites and titanites were covered in poster oral presentations by Julian Haines and Stephanie Rath.

The last session of the first day was devoted to a recent sad event that had deeply touched many members of the high-pressure community. Jean-Michel Besson ("Michel" to his friends and colleagues), who was a mentor, friend or collaborator for many of the participants in the Workshop, died in February 2001. Michel made exceptional contributions to modern high-pressure science, especially in recent times by developing the Paris-Edinburgh pressure cell. Many of us will long remember his remarkable activity and enthusiasm. The four talks of the memorial session were given by Michel’s ex-colleagues or students: Alain Polian (successor to Michel as Director of the Laboratoire Physique des Milieux Condensés), Paul Loubeyre (Michel’s student in the 1980s), Stefan Klotz (one of Michel’s closest collaborators in recent years) and Yann Le Godec (Michel’s last PhD student). The talks covered Michel’s many seminal contributions to high-pressure science, with highlights taken from studies of light elements under pressure, neutron results on high-density amorphous ice and progress in high P-T neutron diffraction. The session was introduced and chaired by Richard Nelmes, who had been Michel’s collaborator for the past 12 years on the Paris-Edinburgh project.

A session on magnetic crystallography opened the second day. Paula Cadavez-Peres, Kenji Ohwada, Jean-Michel Mignot and Anne-Katrin Klehe emphasized highly unusual physical phenomena in magnetically unstable compounds, spin-ladders, intermediate valence systems, and organic superconductors under high pressure. The experimental methods ranged from neutron and x-ray diffraction to optical spectroscopy. All the speakers managed to keep their talks (involving rather "heavy" physics) lively and understandable. Nolwenn Kernavanois and Abdul Hannan complemented the oral talks by presenting poster orals on recent advances in resonant x-ray scattering at the ESRF and neutron diffraction under pressure at the Japanese neutron facility JAERI.

The next session was devoted to studies of ices and hydrates. Rapid developments in this field were illustrated in talks by Werner Kuhs on intercalation of noble gases in ices, by Hidenosuke Itoh on molecular dynamics simulations in hydrates, and by John Loveday on conditions for the formation of new methane hydrates probably occurring in Saturn’s moon Titan. In a poster oral, Serge Desgreniers covered recent x-ray results on silicon and analogous water clathrates.

Lunch was followed by the main poster session. These three hours at the heart of the meeting were exclusively devoted to viewing more than 60 posters (many of which would have merited oral talks if the program could have been longer!). The posters were displayed in a special area near the conference lecture theatre, and were allowed to stay during the whole Workshop, allowing for many further discussions around the poster boards over the following two days.

The last session of this day was dedicated to new technical developments. Osamu Shimomura described recent high-pressure activities on several beam lines at SPring-8. Russell Hemley gave a talk on new types of anvil (synthetic diamond, moissanite, etc.) which promise to expand the limits for available volumes and maximum pressures in x-ray and neutron studies. David Keen presented a poster oral on recent progress in high-pressure single-crystal neutron diffraction at ISIS. The day finished with an evening party held near the poster area. Participants appreciated excellent French food including famous French cheeses and even more famous French wines. Those who were able to resist wine had the possibility to continue scientific discussions near the poster boards.

Friday’s program was opened by geophysics and geoplanetary science. Recent progress in inelastic x-ray scattering in geophysical materials under pressure was described by Guillaume Fiquet, a possible scenario for chemical reactions in the giant planets was proposed by Robin Benedetti, and studies of Fe-O systems at the Earth’s lower mantle conditions were presented by Leonid Dubrovinsky. A talk on theoretical aspects of the Fe-S system under the conditions of the Mars interior by Paula Martin was complemented by a poster oral on experimental studies of the same system by Chrystele Sanloup.

The rest of Friday’s program focused on inelastic studies and techniques. After a lively opening talk on phonons and structural transformation in solids from John Tse, Wolfgang Sturhahn and Russell Hemley (standing in for Chi-Chang Kao who was not able to attend) spoke on nuclear resonant and inelastic x-ray studies at the APS and the BNL. Then Markus Braden and Denis Kozlenko described progress in inelastic neutron scattering at the LLB and IBR-2. The exclusivity of neutron techniques in providing detailed information on dispersion curves under pressure was questioned by a poster oral on inelastic single-crystal x-ray scattering from Florent Occelli. The afternoon session was followed by a visit to the neutron (LLB) and synchrotron (LURE) sources located near the conference venue. The participants had guided tours through the facilities and high-pressure installations, and we specially thank Markus Braden, Jean-Paul Itié and Laurence Noriez who acted as guides.

The social program culminated on Friday evening with a conference dinner held at the spectacular Breteuil Castle. During the whole evening, the castle and the beautiful park were made exclusively available to the participants. Everyone enjoyed the splendid atmosphere of the XVII^th century castle and a guided tour through its historical rooms. Anyone not interested in French history could walk in the park and communicate with its deers and pheasants. An excellent dinner with traditional French dishes ended a memorable evening.

Next morning the scientific spirit of the Workshop remained high. The program opened with a session on new materials and high-pressure synthesis. Rajeev Ahuja spoke on a new high-pressure phase of TiO₂ and Vladimir Solozhenko presented recent results on ternary C-B-N alloys. Both compounds are believed to be among the hardest known materials but possibly they will not resist polymerized C₆₀! Nadezhda Serebryanaya (poster oral) claimed that this new phase formed from C₆₀ can scratch a diamond. The session was completed by talks from Emmanuel Soignard on new results in high-pressure nitrides and Alfonso San-Miguel on EXAFS and x-ray studies of silicon clathrates.

There followed a session on quasiperiodic and nanomaterials. Anne Sadoc (invited talk) and Tetsu Watanuki (poster oral) gave intriguing examples of x-ray and EXAFS studies of quasicrystals. In their lively talks, Stephane Rols and Surinder Sharma described structural changes and superelastic properties of carbon nanotubes studied by neutron and x-ray diffraction, respectively.

The famous "last but not least" was fully applicable to the closing session of the Workshop on the topic of physical properties. First, Katsuya Shimizu presented striking data on pressure-induced superconductivity in elementary iron (the corresponding paper in "Nature" appeared just at the time of the Workshop). Then Andrew Huxley spoke on the co-existence of magnetism and superconductivity in the UGe₂ compound under pressure. His talk was followed by a poster oral from Emma Pugh on quantum critical behavior in Sr₂RuO₄. The session (and the whole Workshop) was ended by a lively talk on structural instability versus magnetic and electronic instabilities in Eu-phosphides by Mohsen Abd-Elmeguid.

Before finally closing the meeting, Richard Nelmes proposed a vote of thanks to all the local organisers, and Igor Goncharenko in particular, for an outstanding meeting, and presented prizes awarded by the Commission for the best poster presentations. First prize went to Crystele Sanloup for her poster on Fe-S liquid alloys, and equal second prizes went to Nadezhda Serebryanaya for her poster on polymerised C₆₀ phases and Tetsu Watanuki for his poster on quasicrystals.

The four days of exciting scientific program, discussions and cultural events had passed all too quickly, and the Organizers and Commission bade farewell to the participants hoping to meet them again in Geneva at the time of the IUCr Congress in 2002.

Igor Goncharenko and Richard Nelmes