IUCr Congress, Geneva, 10. 8. 2002, Microsymposium M40
Liquids and Amorphous Materials at High Pressure
(Chris Benmore, Osamu Shimomura Chairs)
Chris Tulk (Oak Ridge) gave a lively introduction to the session on the fundamental
complexities of the phase diagram of ice. He presented neutron and X-ray
results clearly showing the formation of several new distinct meta-stable
amorphous forms of ice at ambient pressure, between the well known high and
low density forms. These were obtained by careful annealing and subsequent
relaxation of the high density form. Stefan Klotz (Paris) followed the high
density ice theme with some high quality in-situ neutron diffraction data
taken at 2.2GPa. The data had been cleverly interpreted using the EPSR Monte
Carlo technique to reveal the collapse of the second nearest neighbour shell.
He also suggested that the local structure appeared to resemble that of crystalline
ice VII. Sujatha Sampath (Wyoming) presented neutron and high energy X-ray
diffraction data on permanently densified GeO2 glass (recovered
from 10GPa). The two measurements were combined to extract detailed structural
information. She suggested that the next nearest neighbour oxygen atoms determine
the high pressure phase of the glass, which appeared as a rotation and distortion
of the GeO4 tetrahedra. Takanori Hattori (Keio University) discussed
the structure of liquid group III-V compounds measured using synchrotron
techniques. InSb was studied up to 20GPa and temperatures up to 1300°C,
and showed a clear discontinuity at around 10GPa. The data appeared to be
a mixture of two configurations, namely beta-tin and the bcc phase, which
was most stable in equal proportions. Paul McMillian (UCL) gave a rousing
finale to the session with an inspirational talk on amorphous Si, negative
melting slopes and enthalpic signatures. Above 6GPa he showed a high density
amorphous form of Silicon which relaxes on decompression, and suggested this
amorphous-amorphous phase transition may be linked to an underlying phase
transition in the liquid state.
Chris Benmore, Argonne National Labs. Chicago.