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[Congress Report]

New frontiers in high pressure crystallography

This session focused on experimental, computational and conceptual breakthroughs. M.I. McMahon (Edinburgh U., UK) described promising techniques for obtaining data from one or more single crystals grown in situ in diamond-anvil cells for high-pressure phases previously studied only by powder methods. This allows much more detailed structural information to be obtained - as he illustrated with single-crystal studies of InSb, cerium and barium. I.N. Goncharenko (LLB, Saclay, France and Kurchatov Inst., Moscow, Russia) presented recent magnetic neutron diffraction in the 50 GPa pressure range - well above previous limits. Using a combination of sapphire and diamond opposed-anvil devices, and neutron focusing optics, magnetic structures and phase transitions in the 50 GPa pressure range, and temperatures down to 1.5 K, are being studied in systems such as simple binary compounds of Eu and Gd. K. Knorr (Kiel U., Germany) discussed the pressure dependence of disorder in KPF6 and computer simulation of the reconstructed densities using a flexible evolutionary algorithm. With F. Mädler, he found two pathways for the reorientation of KPF6 at high pressure which together fully explain the shape of the electron density found experimentally. A. Fitch (ESRF, France) described software tools developed in collaboration with A.P. Hammersley and T. Günzel for more flexible data-processing, including automation of the FIT2D package that integrates 2-D images to 1-D profiles to allow routine treatment of hundreds of images for time-resolved in situ studies. The program 'CINDEX' facilitates interactive indexing of 2-theta scans providing a stream-lined interface to a number of standard indexing algorithms. H.F. Grünsteudel (ESRF, France) discussed the advantages of a third-generation light source for studying the Mössbauer effect at high pressure. He explained how the diamond-anvil cell technique is especially suited, and how the next steps will involve the simultaneous heating and pressurizing of samples. Complementary posters from the group described instrumentation used at the ESRF to carry out these experiments and some results on 119Sn. K. Hämäläinen (Helsinki U., Finland) presented the final invited talk on the exciting prospects for inelastic X-ray scattering under high pressure - a unique tool to probe electronic ground state properties of materials. He described successful experiments that confirm the possibility of studying fine structures related to the Fermi surface topology in materials such as sodium at high pressure. Some other interesting developments were outlined in short poster orals - by I.D. Brown (McMaster U., Canada) on using the bond-valence model to simulate the effects of high pressure on structures by increasing ionic charges; by Jay D. Bass (Illinois U., USA) on extending the PT range of Brillouin scattering as a complementary technique to diffraction in studying mineral equations of state; by M. Okube (Osaka U., Japan) on a novel use of EXAFS to make direct determinations of anharmonic effective pair potentials; and by D.P. Kozlenko (Frank Lab., Dubna, Russia) on joint elastic and inelastic neutron scattering studies of ammonium halides under high pressure.

John Parise, Chair