IUCr
Congress, Geneva, 9. 8. 2002, Microsymposium M29
Extremes of Pressure
and Temperature
(Russ Hemley, Martin Kunz Chairs)
This microsymposium, which was organized by the High-Pressure Commission,
highlighted recent developments in direct structural studies of materials
subjected to a broad range of thermodynamic conditions up to megabar pressures
and thousands of degrees. T. S. Duffy (Princeton Univ.) presented an overview
of recently developed radial x-ray diffraction studies of deep Earth materials
using diamond-anvil cells. These studies demonstrate that for the first time
detailed information about elasticity and strength of abundant lower mantle
materials can be obtained directly from measurements at the pressures of
the deep Earth. Continuing the theme of high-pressure geoscience, S. Ono
(Japan Marine Science & Technology Center) discussed new high P-T x-ray
diffraction studies of phase transitions of mantle minerals, including new
results on the complex mineral assemblages peridotite and basalt. C. S. Yoo
(Livermore Nat. Lab.) focused on the extraordinary pressure-induced transformations
of simple molecular systems such as CO2 at high pressure, including
the formation of novel framework and ionic solids. Shifting to high P-T behavior
of fluids, J. H. Eggert (Livermore Nat. Lab.) presented new results on the
transformations of water under pressure that included both x-ray measurements
of structural changes and very recent laser shock studies of pre-compressed
samples that access very high temperature states at higher pressures. G.
Galli (Livemore Nat. Lab.) closed out the session with an overview of state-of-the-art
first-principles simulations of fluids at high pressures and temperatures.
Complementing the experimental talks, she presented new calculations for
H2, H2O, and other systems and highlighted the role
of theory in uncovering new phenomena in these "simple" systems under extreme
conditions. Overall, the microsymposium illustrated the diversity of materials
being investigated, the large number of new experimental and theoretical
techniques being developed, and the implications of the results to a variety
of scientific problems.
Russ Hemley, Geophysical Lab, Washington D.C.